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Originally appearing in Volume V22, Page 573 of the 1911 Encyclopedia Britannica.
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OBJECTS. save in being attention to a special class of objects. First of all, it is noteworthy that both have the same characteristics. Thus, what Hamilton called " the law of limitation " holds of each alike and of either with respect to the other; and it holds too not only of the number of presentations but also of the intensity. We can be absorbed in action just as much as in perception or thought; also, as already said, movements, unless they are mechanical, inhibit ideas; and vice versa, ideas, other than associated trains, arrest movements. Intoxication, hypnotism or insanity, rest or exhaustion, tell on apperception as well as on innervation. The control of thoughts, equally with the control of movements, requires effort; and as there is a strain peculiar to intently listening or gazing, which is known to have a muscular concomitant, so too there is a strain characteristic of recollection and visualization, which may quite well turn out to be muscular too. When movements have to be associated, the same continuous attention is called for as is found requisite in associating sensory impressions; and, when such associations have become very intimate, dissociation is about equally difficult in both cases. There is one striking fact that brings to light the essential sameness of apperception and innervation, cited by Wundt for this very purpose. In so-called " reaction-time " experiments it is found, when the impression to be registered follows on a premonitory signal after a certain brief interval, that then the reaction (registering the impression) is often instantaneous; the reaction-time, in other words, is nil. In such a case the subject is aware not of three separate events, (t) the perception of the impression; (2) the reaction; (3) the perception of this; but the fact of the impression is realized and the registering movement is actualized at once and together the subject is conscious of one act of attention and one only. Theory of Presentations. to. We come now to the exposition of the objects of attention or consciousness, i.e. to what we may call the objective or presentational factor of psychical life. The treatment of this will fall naturally into two divisions. In the first we shall have to deal with its general characteristics and with the fundamental processes which all presentation involves. In view of its general and more or less hypothetical character we may call it the theory of presentation. We can then pass on to the special forms of presentations, known as sensations, percepts, images, &c., and to the special processes to which these forms lead up. This exposition will be simplified if we start with a supposition that will enable us to leave aside, at least for the present, the Assumption difficult question of heredity. We know that in of a psycho- the course of each individual's life there is more logical or less of progressive differentiation or development. Individual. Further, it is believed that there has existed a series of sentient individuals beginning with the lowest form of life and advancing continuously up to man. Some traces of the advance already made may be reproduced in the growth of each human being now, but for the most part such traces have been obliterated. What was experience in the past has become instinct in the present. The descendant has no consciousness of his ancestor's failures when performing by " an untaught ability " what they slowly and perhaps painfully acquired. But, if we are to attempt to follow the genesis of mind from its earliest dawn, it is the primary experience rather than the eventual instinct that we have first of all to keep in view. To this end, then, it is proposed to assume that we are dealing with one individual who has continuously advanced from the beginning of psychical life, and not with a series of individuals of whom all save the first inherited certain capacities from their progenitors. The life-history of such an imaginary individual, that is to say, would correspond with all that was new in the experience of a certain typical series of individuals each of whom advanced a certain stage in mental differentiation. On the other hand, from this history would be omitted that inherited reproduction of the net results, so to say, of ancestral experience, that innate tradition by which alone, under the actual conditionsof existence, progress is possible. The process of thus reproducing the old might differ as widely from that of producing the new as electrotyping does from engraving. However, the point is that as psychologists we know nothing directly about it; neither can we distinguish precisely at any link in the chain of life what is old and inherited—original in the sense of Locke and Leibnitz —from what is new or acquired—original in the modern sense. But we are bound as a matter of method to suppose all complexity and differentiation among presentations to have been originated, i.e. experimentally acquired, at some time or other. So long, then, as we are concerned primarily with the progress of this differentiation we may disregard the fact that it has not actually been, as it were, the product of one hand dealing with one tabula rasa to use Locke's—originally Aristotle's—figure, but of many hands, each of which, starting with a reproduction of what had been wrought on the preceding tabulae, put in more or fewer new touches before devising the whole to a successor who would proceed in like manner. rt. What is implied in this process of differentiation and what is it that becomes differentiated ?—these are the questions to which we must now attend. Psychologists have The pre. usually represented mental advance as consisting sentationfundamentally in the combination and recombina- Continuum. tion of various elementary units, the so-called sensations and primitive movements: in other words, as consisting in a species of " mental chemistry. " If we are to resort to physical analogies at all—a matter of very doubtful propriety—we shall find in the growth of a seed or an embryo far better illustrations of the unfolding of the contents of consciousness than in the building up of molecules: the process seems much more a segmentation of what is originally continuous than an aggregation of elements at first independent and distinct. Comparing higher minds or stages of mental development with lower—by what means such comparison is possible we need not now consider—we find in the higher conspicuous differences between presentations which in the lower are indistinguishable or absent altogether. The worm is aware only of the difference between light and dark. The steel-worker sees half a dozen tints where others see only a uniform glow. To the child, it is said, all faces are alike; and throughout life we are apt to note the general, the points of resemblance, before the special, the points of difference. But even when most definite, what we call a presentation is still part of a larger whole. It is not separated from other presentations, whether simultaneous or successive, by something which is not of the nature of presentation, as one island is separated from another by the intervening sea, or one note in a melody from the next by an interval of silence. In our search for a theory of presentations, then, it is from this " continuity of consciousness " that we must take our start. Working backwards from this as we find it now, we are led alike by particular facts and general considerations to the conception of a totum objectivism or objective continuum which is gradually differentiated, thereby giving rise to what we call distinct presentations, just as some particular presentation, clear as a whole, as Leibnitz would say, becomes with mental growth a complex of distinguishable parts. Of the very beginning of this continuum we can say nothing; absolute beginnings are beyond the pale of science. Experience advances as this continuum is differentiated, every differentiation being a change of presentation. Hence the commonplace of psychologists—We are only conscious as we are conscious of change. But " change of consciousness" is too loose an expression to take the place of the unwieldy phrase differentiation of a presentation-continuum, to which we have been driven. For not only does the term "consciousness" confuse what exactness requires us to keep distinct, an activity and its object, but also the term "change" fails to express the characteristics which distinguish new presentations from other changes. Differentiation implies that the simple becomes complex or the complex more complex; it implies also that this increased complexity is due to the persistence of former changes; we may even say such persistence is GradualDlferentiatlon of PresenfationContinuum. essential to the very idea of development or growth. In trying, not the whole of it, for in this experience of massive sensation alone it is impossible to find other elements which an analysis of spatial intuition unmistakably yields. Extensity and extension, then, are not to be confounded. Now, we find, even at our level of mental evolution, that an increase in the intensity of a sensation is apt to entail an increase in its extensity too. In like manner we observe a greater extent of movement in emotional expression when the intensity of the emotion increases. Even the higher region of imagination is no exception, as is shown by the whirl and confusion of ideas incident to delirium, and, indeed, to all strong excitement. But this " diffusion " or " radiation, " as it has been called, diminishes as we pass from the class of organic sensations to the sensations of the five senses, from movements expressive of feeling to movements definitely purposive, and from the tumult of ideas excited by passion to the steadier sequences determined by efforts to think. Increased differentiation seems, then, to be intimately connected with increased "restriction." Probably there may be found certain initial differentiations which for psychology are ultimate facts that it cannot explain. As already said, the very beginning of experience is beyond us, though it is our business—working from within—to push back our analysis as far as we can. But some differentiations being given, then it may be safely said that, in accordance with what we have called the principle of subjective selection (see § 6), attention would be voluntarily concentrated upon certain of these and upon the voluntary movements specially connected with them. To such subjectively initiated modifications of the presentation-continuum, moreover, we may reasonably suppose "restriction" to be in large measure due. But increased restriction would render further differentiation of the given whole of presentation possible, and so the two processes might supplement each other. These processes have now proceeded so far that at the level of human consciousness we find it hard to form any tolerably clear conception of a field of consciousness in which an intense sensation, no matter what, might—so to say—diffuse over the whole. Colours, e.g. are with us so distinct from sounds that—except as regards the excitement of attention or the drain upon it—there is nothing in the intensest colour to affect the simultaneous presentation of a sound. But at the beginning whatever we regard as the earliest differentiation of sound might have been incopresentable with the earliest differentiation of colour, if sufficiently diffused, much as a field of sight all blue is now incopresentable with one all red. Or, if the stimuli appropriate to both were active together, the resulting sensation might have been not a blending of two qualities, as purple is said to be a blending of red and violet, but rather a neutral sensation without the specific qualities of either. Now, on the other hand, colours and sounds are necessarily so far localized that we are directly aware that the eye is concerned with the one and the ear with the other. This brings to our notice a fact so ridiculously obvious Theo- that it has never been deemed worthy of mention, Present-although it has undeniably important bearings— ability. the fact, viz. that certain sensations or movements are an absolute bar to the simultaneous presentation of other sensations or movements. We cannot see an orange as at once yellow and green, though we can feel it at once as both smooth and cool; we cannot open and close the same hand at the same moment, but we can open one hand while closing the other. Such incopresentability or contrariety is thus more than mere difference, and occurs only between presentations belonging to the same sense or to the same group of movements. Strictly speaking, it does not always occur even then; for red and yellow, hot and cold, are presentable together provided they have certain other differences which we shall meet again presently as differences of " local sign. " 12. In the preceding paragraphs we have had occasion to distinguish between the presentation-continuum or whole field of consciousness, as we may for the present call it, Retentive. and those several differentiations within this field ness. which are ordinarily spoken of as presentations, and to which—now that their true character as parts is clear— then, to conceive our psychological individual in the earliest stages of development we must not picture him as experiencing a succession of absolutely new sensations, which, coming out of nothingness, admit of being strung upon the " thread of consciousness " like beads picked up at random, or cemented into a mass like the bits of stick and sand with which the young caddis covers its nakedness. The notion, which Kant has done much to encourage, that psychical life begins with a confused manifold of sensations—devoid not only of logical but even of psychological unity—is one that becomes more inconceivable the more closely we consider it. An absolutely new presentation, having no sort of connexion with former presentations till the subject has synthesized it with them, is a conception for which it would be hard to find a warrant either by direct observation, by inference from biology, or in considerations of an a priori kind. At any given moment we have a certain whole of presentations, a " field of consciousness, " psychologically one and continuous; at the next we have not an entirely new field but a partial change within this field. Many who would allow this in the case of representations, i.e. where idea succeeds idea by the workings of association, would demur to it in the case of primary presentations or sensations. " For, " they would say, " may not silence be broken by a clap of thunder, and have not the blind been made to see? " To urge such objections is to miss the drift of our discussion, and to answer them may serve to make it clearer. Where silence can be broken there are representations of preceding sounds and in all probability even subjective presentations of sound as well; silence as experienced by one who has heard is very different from the silence of Condillac's statue before it had ever heard. The question is rather whether such a conception as that of Condillac's is possible; supposing a sound to he, qualitatively, entirely distinct from a smell, could a field of consciousness consisting of smells be followed at once by one in which sounds had part? And, as regards the blind coming to see, we must remember not only that the blind have eyes but that they are descended from ancestors who could see. What nascent presentations of sight are thus involved it would be hard to say; and the problem of heredity is one that we have for the present left aside. The view here taken is (I) that at its first appearance in psychical life a new sensation or so-called elementary presentation is really a partial modification of some pre-existing presentation which thereby becomes as a whole more complex than it was before; and (2) that this complexity and differentiation of parts never become a plurality of discontinuous presentations, having a distinctness and individuality such as the atoms or elementary particles of the physical world are supposed to have. Beginners in psychology, and some who are not beginners, are apt to be led astray by expositions which set out from the sensations of the special senses, as if these furnished us with the type of an elementary presentation. The fact is we never experience a mere sensation of colour, sound, touch, and the like; and what the young student mistakes for such is really a perception, a sensory presentation combined with various sensory and motor presentations and with representations—and having thus a definiteness and completeness only possible to complex presentations. 1^Ioreover, if we could attend to a pure sensation of sound or colour by itself, there is much to justify the suspicion that even this is complex and not simple, and owes to such complexity its clearly marked specific quality. In certain of our vaguest and most diffused organic sensations there is probably a much nearer approach to the character of the really primitive presentations. In such sensations we can distinguish three variations, viz. variations of quality, of intensity, and of what Bain called Diffusion massiveness, or, as we shall say, extensity. This and last characteristic, which everybody knows who Restriction. knows the difference between the ache of a big bruise and the ache of a little one, between total and partial immersion in a bath, is, as we shall see later on, an essential element in our perception of space. But it is certainly we too may confine the term. But it will be well in the next place, before inquiring more closely into their characteristics, to consider for a moment that persistence of preceding modifications which the principle of progressive differentiation implies. This persistence is best spoken of as retentiveness. It is often confused with memory, though this is something much more complex and special; for in memory there is necessarily some contrast of past and present, whereas here there is simply the persistence of the old. But what is it that persists? On our theory we must answer, the continuum as differentiated, not the particular differentiation as an isolated unit. If psychologists have erred in regarding the presentations of one moment as merely a plurality of units, they have erred in like manner concerning the so-called residua of such presentations. As we see a certain colour or a certain object again and again, we do not go on accumulating images or representations of it, which are somewhere crowded together like shades on the banks of the Styx; nor is such colour, or whatever it be, the same at the hundredth time of presentation as at the first, as the hundredth impression of a seal on wax would be. There is no such lifeless fixity in mind. .The explanations of perception most in vogue are far too mechanical and, so to say, atomistic; but we must fall back upon the unity and continuity of our presentation-continuum if we are to get a better. Suppose that in the course of a few minutes we take half a dozen glances at a strange and curious flower. We have not as many complex presentations which we might symbolize as Fi, F2, .... F6. But rather, at first only the general outline is noted, next the disposition of petals, stamens, &c., then the attachment of the anthers, position of the ovary, and so on; that is to say, symbolizing the whole flower as [p'(ab) s' (c d) o' (f g)], we first apprehend say [p'.. s' ..o'], then [p' (a b) s'.. o'.], or [p' (a..) s' (c..) o' (L.)), and so forth. It is because the traits first attended to persist that the later form an addition to them till the complex is at length complete. There is nothing in this instance properly answering to what are known as the reproduction and association of ideas; in the last and complete apprehension as much as in the first vague and inchoate one the flower is there as a primary presentation. There is a limit, of course, to such a procedure, but the instance taken, we may safely say, is not such as to exceed the bounds of a simultaneous field of consciousness. Assuming then that such increase of differentiation through the persistence of preceding differentiations holds of the presentation-continuum as a whole, we conclude that, in those circumstances in which we now have a specific sensation of, say, red or sweet, there would be for some more primitive experience nothing but a vague, almost organic, sensation, which, however, would persist, so that on a repetition of the circumstances it could be again further differentiated. The earlier differentiations, in short, do not disappear like the waves of yesterday in the calm of to-day, nor yet last on like old scars beside new ones; but rather the two are blended and combined, so that the whole field of consciousness, like a continually growing picture, increases indefinitely in complexity of pattern. 13. Assimilation.—This process, in which later differentiations blend with and thereby further restrict and specialize what is retained of earlier and less definite presentations, is thus a further implication of the principle of the progressive development of the presentational continuum. When not ignored altogether this further process has been commonly regarded as merely a simple form of " association," its peculiarity being, as it was supposed, that the presentations associated—though numerically distinct—were in quality perfectly identical. In point of fact, both these assumptions seem to be erroneous and due to the so-called psychologist's fallacy.' For the experiencing subject there is apparently at this stage—as we have already urged—neither the numerical distinctness nor the qualitative identity which the words " past impression (A1) " and " present impression (A2) " suggest. Still the connexion between this process of mere blending or fusion, which we shall call assimilation, and the process of association proper is so close, and the detailed analysis called for so complex, that we must needs defer further discussion till we come to treat of association as a whole (cf. below, § 24). It may then be possible to show that we have here to do with a process As, e.g. in interpreting the conduct of children as if they were already " grown-up " persons; cf. J. Ward, R. of Spec. Phily. (1882), pp. 369 fn. 374; James, Prin. of Psychy. (189o), i. 196.much simpler and more fundamental than association. But it is at least clear at once that if the term association is to be correctly used it will imply that the presentations associated are from the first distinct, are attended to as distinct, are associated solely in consequence of such attention, and remain to the last distinguishable. In view of the intimate connexion between differentiation, retentiveness and assimilation it will sometimes be convenient to refer to all three together as constituting what we may call the plasticity of the presentational continuum. 14. This will be the most convenient place to take note of certain psychological doctrines which, though differ- Relativity. ing in some material respects, are usually included under the term Law of Relativity. a. Hobbes's Sentire semper idem et non sentire ad idem recidunt is often cited as one of the first formulations of this law; and if we take it to apply to the whole field of consciousness it becomes at once true and trite: a field of consciousness unaltered either by change of impression or of idea would certainly be a blank and a contradiction. Understood in this sense the Law of Relativity amounts to what Hamilton called the Law of Variety: " that we are conscious only as we are conscious of difference." z But, though consciousness involves change, it is still possible that particular presentations in the field of consciousness may continue unchanged indefinitely. When it is said that " a constant impression is the same as a blank," what is meant turns out to be something not psychological at all, as, e.g., our insensibility to the motion of the earth or to the pressure of the air—cases in which there is obviously no presentation, nor even any evidence of nervous change. Or else this paradox proves to be but an awkward way of expressing what we may call accommodation, whether physiological or psychological. Thus the skin soon adapts itself to certain seasonal alterations of temperature, so that heat or cold ceases to be felt: the sensation ceases because the nervous change, its proximate physical counterpart, has ceased. Again, there is what James Mill calls " an acquired incapacity of attention," such that a constant noise, for example, in which we have no interest, is soon inaudible. In such a case of psychological accommodation we should expect also to find on the physiological side some form of central reflection or isolation more or less complete. As a rule, no doubt, impressions do not continue constant for more than a very short time; still there are sad instances enough in the history of disease, bodily and mental, to show that such a thing can quite well happen, and that such constant impressions (and " fixed ideas," which are in effect tantamount to them), instead of becoming blanks, may dominate the entire consciousness, colouring or bewildering everything. b. From the fact that the field of consciousness is continually changing it has been supposed to follow, not only that a constant presentation is impossible, but—as a further consequence—that every presentation is essentially nothing but a transition or difference. " All feeling," says Bain, the leading exponent of this view, is two-sided. . . . We may attend more to one member of the couple than to the other. . . . We are more conscious of heat when passing to a higher temperature, and of cold when passing to a lower. The state we have passed to is our explicit consciousness, the state we have passed from is our implicit consciousness." But the transition need not be from heat to cold, or vice versa: it can equally well take place from a neutral state, which is indeed the normal state, of neither heat nor cold; a new-born mammal, e.g. must experience cold, having never experienced heat. Again, suppose a sailor becalmed gazing for a whole morning upon a stretch of sea and sky, what sensations are implicit here? Shall we say yellow as the greatest contrast to blue, or darkness as the contrary of light, or both ? What, again, is the implicit consciousness when the explicit is sweet; is it bitter or sour, and from what is the transition in such a case ? For one thing it seems clear that the transition of attention from one presentation to another and the differences between the presentations themselves are distinct facts. It is strange that the psychologist who has laid such stress on neutral states of surprise 2 The Works of Thos. Reid, supplementary note, p. 932. as being akin to feeling and so distinct from special presentations, should in any way confound the two. The mistake is perhaps accounted for by the fact that Bain, in common with the rest of his school, nowhere distinguishes between attention and the presentations that are attended to. If " change of impression " and being conscious or mentally alive are the same thing, it is then manifestly tautologous to say that one is the indispensable condition of the other. If they are not the same thing, then the succession of shocks or surprises cannot wholly determine the impressions which successively determine them. But we have still to consider whether the impressions them-selves are nothing but differences or contrasts. " We do not know any one thing of itself but only the difference between it and another thing," said Bain. But it is plain we cannot speak of contrast or difference between two states or things as a contrast or difference, if the states or things are not themselves presented; the so-called contrast or difference would then be itself a single presentation, and its supposed " relativity " but an inference. Difference is not more necessary to the presentation of two objects than two objects to the presentation of difference. And, what is more, a difference between presentation is not at all the same thing as the presentation of that difference. The former must precede the latter; the latter, which requires active comparison, need not follow. There is an ambiguity in the words " know," " knowledge," which Bain seems not to have considered: " to know " may mean either to perceive or apprehend, or it may mean to understand or comprehend.' Knowledge in the first sense is only what we shall have presently to discuss as the recognition or assimilation of an impression (see below, § 18); knowledge in the latter sense is the result of intellectual comparison and is embodied in a proposition. Thus a blind man who cannot know light in the first sense can know about light in the second if he studies a treatise on optics. Now in simple perception or recognition we cannot with any exactness say that two things are perceived: straight is a thing, i.e. a definite object presented; not so not-straight, which answers to no definite object at all. Only when we rise to intellectual know-ledge is it true to say: " No one could understand the meaning of a straight line without being shown a line not straight, a bent or crooked line." 2 Two distinct presentations are necessary to the comparison that is here implied; but we must first re-cognize our objects before we can compare them, and this further step we may never take. We need, then, to distinguish between the comparativity of intellectual knowledge, which we must admit—for it rests at bottom on a purely analytical proposition—and the " differential theory of presentations," which, however plausible at first sight, must be wrong somewhere, since it commits us to absurdities. Thus, if we cannot have a presentation X but only the presentation of the difference between Y and Z, it would seem that in like manner we cannot have the presentation of Y or Z, nor therefore of their difference X, till we have had the presentation of A and B say, which differ by Y, and of C and D, which we may suppose differ by Z. The lurking error in this doctrine, that all presentations are but differences, may perhaps emerge if we examine more closely what may be meant by difference. We may speak of (a) differences in intensity between sensations supposed to be qualitatively identical, as e.g. between the taste of strong and weak tea; or of (b) differences in quality between presentations of the same sense, as e.g. between red and green; or of (c) differences between presentations of distinct senses, as e.g. between blue and bitter. Now as regards (a) and (b), it will be found that the difference between two intensities of the same quality, or between two qualities of the same order, may be itself a distinct pre- ' Other languages give more prominence to this distinction; compare yvanes& and ei&Evae, noscere and scire, kennen and wissen, connaitre and savoir. On this subject there are some acute remarks in a little-known book, the Exploratio philosophica, of Professor J. Grote. Hobbes, too, was well awake to this difference, as e.g. when he says, " There are two kinds of knowledge; the one, sense or know-ledge original and remembrance of the same; the other, science or knowledge of the truth of propositions, derived from understanding." Bain, Logic, i. 3.sentation, that is to say, in passing from a load of io lb to one of 20 lb, for example, or from the sound of a note to that of its octave, it is possible to experience the change continuously, and to estimate it as one might the distance between two places on the same road. But nothing of this kind holds of (c).3 In passing from the scent of a rose to the sound of a gong or a sting from a bee we have no such means of bringing the two into relation—scarcely more than we might have of measuring the length of a journey made partly on the common earth and partly through the looking-glass. In (c), then, we have only a diversity of presentations, but not a special presentation of difference; and we only have more than this in (a) or (b) provided the selected presentations occur together. We say that we know the difference between a sound and a taste; but what we mean is simply that we know what it is to pass from attending to the one to attending to the other. It is simply an experience of change. Change, however, implies continuity, and there is continuity here in the movement of attention and the affective state consequent on that, but not directly in the qualities themselves. c. If red follows green we may be aware of a greater difference than we could if red followed orange; and we should ordinarily call a ro lb load heavy after one of s lb and light after one of 20 lb. Facts like these it is which make the differential theory of presentations plausible. On the strength of such facts Wundt has formulated a law of relativity, free, apparently, from the objections just urged against Bain's doctrine. It runs thus: " Our sensations afford no absolute but only a relative measure of external impressions. The intensities of stimuli, the pitch of tones, the qualities of light, we apprehend (empfinden) in general only according to their mutual relation, not according to any unalterably fixed unit given along with or before the impression itself."' But if true this law would make it quite immaterial what the impressions themselves were: provided the relation continued the same, the sensation would be the same too, just as the ratio of 2 to 1 is the same whether our unit be miles or millimetres. In the case of intensities, e.g. there is a minimum sensibile and a maximum sensibile. The existence of such extremes is alone sufficient to turn the flank of the thoroughgoing relativists; but there are instances enough of intermediate intensities that are directly recognized. A letter-sorter, for example, who identifies an ounce or two ounces with remarkable exactness identifies each for itself and not the first as half the second; of an ounce and a half or of three ounces he may have a comparatively vague idea. And so generally within certain limits of error, indirectly ascertained, we can identify intensities, each for itself, neither referring to a common standard nor to one that varies from time to time—to any intensity, that is to say, chat chances to be simultaneously presented; just as an enlisting sergeant will recognize a man fit for the Guards without a yard measure and whether the man's comrades are tall or short. As regards the qualities of sensations the outlook of the relativists is, if anything, worse. In what is called Meyer's experiment (described under Vision) what appears greenish on a red ground will appear of an orange tint on a ground of blue; but this contrast is only possible within certain very narrow limits. In fact, the phenomena of colour-contrast, so far from proving, distinctly disprove that we apprehend the qualities of light only according to their mutual relation. In the case of tones it is very questionable whether such contrasts exist at all. Summing up on the particular doctrine of relativity of which Wundt is the most distinguished adherent, the truth seems to be that, in some cases where two presentations whose difference is itself present-able occur in close connexion, this difference—as we indirectly learn—exerts a certain bias on the assimilation or identification ' Common language seems to recognize some connexion even here or we should not speak of harsh tastes and harsh sounds, or of dull sounds and dull colours and so forth. All this is, however, super-added to the sensation, probably on the ground of similarities in the accompanying organic sensations. Physiologische Psychologie, 1st ed., p. 421; the doctrine reappears in later editions, but no equally general statement of it is given. of one or both of the presentations. There is no " unalterably fixed unit " certainly, but, on the other hand, " the mutual relations of impressions " are not everything. 15. The term " field of consciousness " has occurred sundry times in the course of this exposition: it is one of several em-.Subcon- ployed in describing what have been incidentally sciousness. referred to as " degrees or grades of consciousness " —a difficult and perplexing topic that we must now endeavour further to elucidate. Sailors steering by night are said to look at the pole-star, " the cynosure of every eye," but this does not prevent them from seeing the rest of the starry vault. At a conversazione we may listen to some one speaker while still hearing the murmur of other voices, and while listening we may also see the speaker and thereby identify him the better. What in these instances is looked at or listened to has been called the " focus " of consciousness, the rest of what is heard or seen or otherwise presented being called the " field " within which attention is thus concentrated or brought to a point. Of these objects beyond the focus we have then only a lower degree of consciousness, and the more " distant " they are from the centre of interest the fainter and obscurer they are supposed to be or to become. Now, it is obvious that the continuity here implied, if strictly taken, logically commits us to a field of consciousness extending with ever diminishing intensity ad indefinitum. But we have next to notice certain new 'features that have led psychologists to give to the term field of consciousness a more restricted meaning. A meteor flashing across the sky would certainly divert the helmsman's attention, and for the nonce he would look at that and not at the star in the Little Bear's tail; a voice at our elbow accosting us, we should turn to the new speaker and listen to him, still hearing it may be, but no longer " following," the discourse thus for us interrupted. In these cases a change in the field of consciousness brings about a non-voluntary change in the focus. But it only does so provided it is sufficiently intense and abrupt, and the more attention is already concentrated the less effective a given disturbance will be. A whole swarm of meteors might have streaked the sky unheeded while Ulysses, life in hand, steered between Scylla and Charybdis, just as all the din of the siege failed to distract Archimedes bent over his figures in the sand. On the other hand, we can voluntarily transfer the focus of consciousness to any object within the field, provided again this is sufficiently differentiated from the rest. But, more than that, we can not only of our own motion turn to lock at or to listen to what we have only seen or heard, but not noticed before; we can also look out or listen for something not as yet distinguish-able, perhaps not as yet existing at all. And here again the concentration of attention may be maximal, as when a shipwrecked crew scan the horizon for a sail, or a beleaguered troop hearken for the oncoming of rescue. Now, such anticipated presentations as soon as they are clearly discernible have already a certain finite intensity, and so they are said to have passed over " the threshold "—to use Herbart's now classic phrase—and to have entered the field of consciousness. Afterwards any further increase in their intensity is certainly gradual; are we then to suppose that before this their intensity changed instantly from zero to a finite quantity and not rather that there was an ultraliminal or subliminal phrase where too it only changed continuously? The latter alternative constitutes the hypothesis of subconsciousness. According to this hypothesis the total field with which we began is divided into two parts by what Fechner emphatically called "the fact of the threshold," and the term field of consciousness is henceforth restricted to that part within which the focus of consciousness always lies, the outlying part being the region of subconsciousness. Difficulties now begin to be apparent. The intensity or vivacity of a presentation within the field of consciousness depends partly on what we may call its inherent or absolute intensity, partly on the attention that it receives; but this does not hold of presentations in subconsciousness. These sub-presentations, as we ought perhaps to call them, cannot be severally and selectively attended to,cannot be singled out as direct objects of experience. Many psychologists have accordingly maintained not only that they cannot with propriety be called presentations, but that they have no strictly psychical existence at all. This, however, is too extreme a view. If nothing of a presentational character can exist save in the field of consciousness as thus circumscribed by a definite boundary or threshold, a breach of continuity is implied such as we nowhere else experience: even the field of sight, from which the metaphor of a field of consciousness is derived, has no such definite margin. The threshold then is not comparable to a mathematical line on opposite sides of which there is an intensive discontinuity. This has been amply proved by the psychophysical investigations of Fechner and others. We listen, say, to a certain sound as it steadily diminishes; at length we cease to hear it. Again, we listen for this same sound as it steadily increases and presently just barely hear it. In general it is found that its intensity in the former case is less than it is in the latter, and there is also in both cases a certain margin of doubt between clear presence and clear absence; the presentation seems to flicker in and out, now there and now gone. Further, in comparing differences in sensations—of weight, brightness, temperature, &c.—we may fail wholly to detect the difference between a and b, b and c, and yet the difference between a and c may be clearly perceived. We have thus to recognize the existence of a difference between sensations, although there is no so-called " sensation of difference." But if this much continuity must be admitted we can hardly fail to admit more. If differences of presentation exist within the field of consciousness beyond the outermost verge of the " threshold of difference," we cannot consistently deny the existence of any presentations at all beyond the threshold of consciousness. Since the field of consciousness varies greatly and often suddenly with the amount and distribution of attention, we must, as already said, either recognize such subconscious presentations or suppose that clearly differentiated presentations, presentations that is to say of finite intensity, pass abruptly into or out of existence with every such variation of the field. The hypothesis of subconsciousness, then, is in the main nothing more than the application to the facts of presentation of the law of continuity, its introduction into psychology being due to Leibnitz, who first formulated that law. Half the difficulties in the way of its acceptance are due to our faulty terminology. With Leibnitz consciousness was not coextensive with all psychical life, but only with certain higher phases of it.' Of late, however, the tendency has been to make consciousness cover all stages of mental development, and all grades of presentation, so that a presentation of which there is no consciousness resolves itself into the manifest contradiction of an unpresented presentation—a contradiction not involved in Leibnitz's " unapperceived perception." But such is not the meaning intended when it is said, for example, that a soldier in battle is often unconscious of his wounds or a scholar unconscious at any one time of most of the knowledge " hidden in the obscure recesses of his mind." There would be no point in saying a subject is not conscious of what is not presented at all; but to say that what is presented lacks the intensity requisite in the given distribution of attention to change that distribution appreciably is pertinent enough. Subconscious presentations may tell on conscious life—as sunshine or mist tells on a landscape, or the underlying writing on a palimpsest—although . lacking either the intensity or the individual distinctness requisite to make them definite features. Even if there were no facts to warrant 1 The following brief passage from his Principes de la nature et de la grace (§ 4) shows his meaning: " II est bon de faire distinction entre la Perception, qui est 1'etat inti rieur de la Monade representant les choses externes, et l'Apperception, qui est la Conscience, ou la connaissance reflexive de cet etat interieur, laquelle nest point donne a toutes les Imes, ni toujours d la name time. Et c'est faute de cette distinction que les Cartesiens ont manque, en comptant pour rien les perceptions dont on ne s'appercoit pas, comme le peuple compte pour rien les corps insensibles ' (Op. Phil. Erdmann's ed., P. 715). this concept of an ultra-liminal presentation of impressions it might still claim an a priori justification. The subconscious presentation of ideas as distinct from impressions calls, however, for some special consideration. As we can turn our attention to the sensory threshold subcon- and await the entrance of an expected impression, scions Ideas. so we may await the emergence of a "memory-image "; and again the threshold turns out to be not a mathematically exact boundary but a region of varying depth). What we are trying to recollect seems first to waver, now at the tip of our tongue and the next moment completely gone, then perhaps a moment afterwards rising into clear consciousness. Sometimes when asked, say, for the name of a certain college contemporary we reply: I cannot tell, but I should know the name if I heard it. We are aware that we could " recognize," though we cannot " reproduce. " At other times we are confident that even recognition is no longer possible, and still if we met the man himself in the old scenes and heard his voice his name might yet recur. Nevertheless, it may be urged, it is surely incredible that all the incidents of a long lifetime and all the items of knowledge of a well-stored mind that may possibly recur—" the infinitely greater part of our spiritual treasures," as Hamilton says—are severally retained and continuously presented in the form and order in which they were originally experienced or acquired. This, however, is not implied. Images in contrast to impressions have always a certain generality. The same image may figure in very various connexions, as may the same letter, for example, in many words, the same word in many sentences. We cannot measure the literature of a language by its vocabulary, nor may we equate the extent of our " spiritual treasures " when these are successively unfolded with the psychical apparatus, so to say, in which they are subconsciously involved? Take the first book of the Aeneid, which, as Macaulay would say, every schoolboy knows: as subconsciously involved, when the boy is not thinking of it, his knowledge is more comparable to a concordance than to the text itself, which nevertheless can be reproduced from it. In the text Aeneas occurs many times, in the concordance as a heading but once. But give him the cue Aeneas scopulum, and the boy reels off from the 18oth line; or Praecipue Pius Aeneas, and he starts with the 22oth. But ask him for the 58oth line; he is probably helpless, while a dunce with the book in his hand can read it off at once. Say instead Et pater Aeneas, and the boy can straightway complete the line while the dunce is now helpless. So though its explicit revival is successional, occurs, so to say, in single file, a whole scheme in which many ideas are involved may rise towards the threshold together. When our schoolboy, for example, turns from classics to geography, the mention of Atlas, which might then have recalled a Titan, now leads him to think only of his book of maps. And there is a like sudden shifting of the substratum of our thoughts, when, taking up the morning paper, we glance first at the foreign telegrams, then at the money market, and then at the doings of our political friends. Yet more remote than all, obscurer but more pervasive, like the clouds of cherubs or imps vaguely limned in medieval pictures, are the indefinite constituents of our emotional atmosphere, " gay motes that people the sunbeams " of our cheerfulness and make all couleur de rose, or " horrid shapes and sights unholy " that overcast the outlook when we " have the blues." And as attention relaxes, these advance into the foreground and become more or less palpable hopes or fears. Herbart and Fechner describe subconscious presentations generally as existing below the threshold. On the other hand, we have spoken of subconscious sensations as existing beyond it. In view of the important differences between the two forms of presentations primary and secondary, this distinction of ultra-liminal and subliminal seems convenient and justifiable. ' This doctrine of the involution and evolution of ideas we owe to Leibnitz. Herbart attempted in a very arbitrary and a priori fashion to develop it into a physical statics and dynamics with the result—usual to extreme views—that later psychologists neglected it altogether. There are now signs of a fresh reaction, and we shall continually come across evidence of the wide range and great importance of the doctrine as we proceed. Because of the manifold forms into which they may evolve, subconscious images, while still involved, are sometimes called " psychical " or more definitely " presentational dispositions." The word disposition means primarily an arrangement, as when we talk of the disposition of troops in a battle or of cards in a game; the disposita, that is to say, are always something actual. Which of several potential dispositions they will actually assume will depend upon circumstances, but at least, as Leibnitz long ago maintained, " les puissances veritables ne sont jamais des simples possibilites." What is requisite to the realization of a given potentiality is sometimes a condition to be added, sometimes it is one to be taken away. A locomotive with the fire out has no tendency to move, but with steam up it is only hindered from moving by the closure of the throttle-valve or the friction of the brake. Now presentational dispositions we assume to be of the latter sort. They are processes or functions more or less inhibited, and the inhibition is determined by their relation to other psychical processes or functions. The analysis and genesis of these presentational interactions will occupy us at length by and by; it may then be possible to explain the gradual involution of what was successively unfolded in explicit consciousness into those combinations which Herbart called " apperception-masses," combinations devoid of the concrete hints of date and place which are essential to memory. Meanwhile the evidence adduced—decidedly cogent though admittedly indirect—together with the difficulties besetting the extreme view that beyond or below the threshold of consciousness there is nothing presentational, seems clearly to justify the hypothesis of subconsciousness. At the same time the principle of continuity, everywhere of fundamental importance when we are dealing with reality, forbids the attempt arbitrarily to assign any limits to the subconscious. Many psychologists have proposed to explain subconscious retention by habit. But it is obvious that habit itself implies retention and is practically synonymous with disposition; it must therefore presuppose disposita if we are to escape the absurdities of puissances ou facultes nues, with which in this very connexion Leibnitz twitted Locke. Yet, obvious as all this may be, it is frequently ignored even by those who are fond of exposing the pretended explanations of the " faculty-psychologists " and quoting Moliere to confute them. Thus we find J. S. Mill arguing: " I have the power to walk across the room though I am sitting in my chair: but we should hardly call this power a latent act of walking." Nor should we call it a power at all if Mill had been paralysed, or if, instead of sitting in his chair, he had been lying in his cradle. What we want is the simplest psychological description of the situation after the power has been acquired by practice and is still retained. In such a case we can be conscious of the " idea " of the movement without the movement actually ensuing; yet only in such wise that the idea is more apt to pass over into action the in-tenser it is, and often actually passes over in spite of us. Surely there must be some functional activity answering to this conscious presentation; why may not a much less amount of it be conceived possible in subconscious presentation? Sensation, Movement and the External World. 16. On the view of experience here maintained, we are bound to challenge the description of sensations' as due to physical stimuli—widely current though it is—as one that is psychologically inappropriate. The UeHnition of following definition, given by Bain, may be taken sensation as a type: " By sensations, in the strict meaning, we under-stand the mental impressions, feelings or states of consciousness following on the action of external things on some part of the body, called on that account sensitive." 6 It is true, no doubt, that what the psychologist calls sensibility has as its invariable concomitant what physiologists call sensibility, 3 Examination of Sir W. Hamilton's Philosophy, 3rd ed., p. 329. ° For a detailed account of the various sensations and perceptions pertaining to the several senses the reader is referred to the articles VISION; HEARING; TOUCH; TASTE; SMELL, &C. 6 Senses and Intellect, 4th ed. (1894), p. Io1. SENSATION] or what the more careful of them call irritability; and, true again, that this irritability is invariably preceded by a physical process called stimulation. But it may be urged, why not recognize a connexion that actually obtains, since otherwise sensation must remain unexplained ? Well, in the first place, such " psychophysical " connexion is not a psychological explanation: it cannot be turned directly to account in psychology, either analytic or genetic. Next the psychological fact called sensation always is, and at bottom always must be, independently ascertained; for the physiological " neurosis " or irritation has not necessarily a concomitant " psychosis " or sensation and, strictly dealt with, affords no hint of such. Finally, this inexplicability of sensation is a psychological fact of the utmost moment: it answers to what we call reality in the primary sense of the term. The psycho-physicist, in setting out to explain sensation, has—unawares to himself—left this fundamental reality behind him. For it belongs essentially to individual experience, and this—in assuming the physical standpoint—he has of course transcended. Nevertheless the mistake of method that here reveals itself was perhaps inevitable, for the facts of another's sense-organs and their physical excitants must have obtruded themselves on observation long before the reflective attitude was advanced enough to make strictly psychological analysis possible. The psychophysical standpoint, that is to say, was attained before the purely psychological; and the consequent bias is only now in process of correction. A series of physical processes, first without and then within the organism—ethereal or aerial vibrations, neural and cerebral excitations—was the starting-point. What comes first, immediately, and alone, in the individual's experience, and is there simply and positively real, was then misinterpreted as subjective modification, mental impression, species sensibiles, or the like. For from the days of Democritus to our own the same crude metaphor has prevailed without essential variation. And here the saying holds: Vestigia nulla retrorsum. Into the man's head the whole world goes, including the head itself. Such thoroughgoing " introjection " affords no ground for subsequent " projection." Thus the endeavour to explain sensation overreaches itself: the external object or thing that was supposed to cause sensations and to be therefore distinct from them, was in the end wholly resolved into these and regarded as built out of them by association (Mill) or by apperceptive synthesis (Kant). But no " mental chemistry," no initial alchemy of " forms," can generate objective reality from feelings or sense-impressions as psychophysically defined.' A's experience as it is for B is not real but inferential; and if the grounds of the inference, which are the only realities for B, are to be regarded as the causes of which A's experiences are merely the effects, then the two experiences are on a wholly different footing. When A treats B in the same fashion we get the world in duplicate: (r) as original and out-side, i.e. as cause, and (2) as copied within each percipient's head, i.e. as effect. But when B interprets his own experience as he had interpreted A's we seem to have lost the real world altogether. In presence of this dilemma, the philosophers of our time, as already said, are feeling it needful to revise their psychology. The question of method is vital. If the psycho-physical standpoint were the more fundamental, psychology would be based on physiology, and the old definition of sensation might stand. If, on the other hand, it is the exclusive business of psychology to analyse and trace the development of individual experience as it is for the experiencing individual, then—however much neurological evidence may be employed as a means of ascertaining psychological facts—the facts them-selves must be scrupulously divested of all physical implications, the psychophysical method takes a secondary place, and the objective reality of " sensory " presentations stands unimpeached. The duality of subject and object in experience compels us also to object to the description of sensations as " states of conscious- ' Nothing shows this more plainly than the newly-coined term epiphenomenon now applied in this connexion561 ness." Since it is the subject, not the object that is conscious, the term state of consciousness implies strictly a subjective reference; and so it is only applicable to sensations, if they are regarded as subjective modifications, either affective or active. The former would identify sensation with feeling, and this—for reasons already given—we must disallow. But it is true that a sensation, like other presentations, implies the subjective activity we call attention; it is not, however, a modification or state of this activity, but the object of it This relation is expressed in German by means of the distinction generally of Vorstellen and Vorstellung and in the present case of Empfinden and Empfindung; and German psychology has gained in clearness in consequence. The distinction of conception and concept (conceit) is to be found in older English writers and was revived by Sir W. Hamilton, who suggested also the analogous distinction of perception and percept. It would be a great gain if there were a corresponding pair of terms to distinguish between " the sensing act " and the object " sensed," as some have been driven to say. Reception and recept at once occur and seem unexceptionable—apart, of course, from their novelty.' At any rate, if we are to rest content with our present untechnical terminology we must understand sensations to mean objective changes as they first break in upon the experience of our psychological individual; in this respect Locke's term " impression " has a certain appropriateness. What we ordinarily call a single sensation has not only a characteristic quality but it is also quantitatively determined in respect of intensity, protensity (or duration) and extensity. A plurality of properties, it may be said, straightway implies complexity of some sort. This is obvious and un- Character` deniable; psychological—as distinct from psychical' Isms of —analysis of simple sensations is possible, and the sensation. description just given is reached by means of it. Such analysis, however, presupposes the comparison of many sensations; but to the complexity it discloses there is no answering plurality discernible in the immediate experience of a single sensation. To make this clearer let us start from a case in which such plurality can be directly verified. In a handful of rose petals we are aware at once of a definite colour, a definite odour and a definite " feel." Here there is a plurality (a+b+c), any part of which can be withdrawn from our immediate experience without prejudice to the rest, for we can close the eyes, hold the nose, or drop the petals on the table. Let us now turn to the colour alone; this we say has a certain quality, in-tensity, extensity, &c. But not only have we not one sense for quality, another for intensity, &c., but we cannot reduce the intensity to zero and yet have the quality remaining; nor can we suppress the quality and still retain the extensity. In this case then what we have is not a plurality of presentations (a+b +c), but a single presentation having a plurality of attributes (a b c) so related that the absence of any one annihilates the whole. But though, as already said, such single presentation gives, as it stands, no evidence of this plurality, yet it is to be remembered that in actual experience we do not deal with sensations in isolation; here, accordingly, we find evidence in plenty to justify our psychological analysis. In innumerable cases we experience varieties of intensity with little or no apparent change of quality, as happens, for example, when a sounding pitch-pipe is moved towards or away from the ear; and continuous changes of quality without any change of in-tensity, as happens when the pipe is shortened or lengthened without any alteration of position. We may have tactual or visual sensations which vary greatly in extensity without any striking change of quality, and we may have such sensations in every possible variety of quality without any changes of extensity. The numerous and striking diversities among our present sensations are obviously not primordial; what account then can we give of their gradual differentiation ? Some psychologists have assumed the existence of absolute " units of Reception does not in English suggest the taking back of the Latin recipere; it expresses only the comparative passivity of sense. In contrast to percipere (to take entire possession of) it implies the absence of that assimilation which is essential to perception; and finally it contrasts appropriately with retention. ' This distinction, though continually overlooked, is vitally important. By psychological analysis we mean such analysis as the psychological observer can reflectively make, by psychical analysis only such analysis as is possible in the immediate experience of the subject observed. sensibility," all identically the same, and explain the unlikenesses in our existing sensations as resulting " from unlike Differentia- modes of integration of these absolute units."' don of The sole evidence on which they rely is physiological, Sensation. the supposed existence of a single nerve shock or neural tremor. It is true that in an extirpated nerve what is known as the " negative variation " is approximately such an isolated event of uniform quality. But the same cannot be said of what happens during the stimulation of a nerve in situ with its peripheral and central connexions still intact. The only evidence apparently to which we can safely appeal in this inquiry is that furnished by biology. Protoplasm, the so-called " physical basis of life," is amenable to stimulation by every form of physical agency—mechanical, chemical, thermal, photical, electrical—with the single exception of magnetism; and in keeping with this it is found that unicellular organisms respond; and respond in ways more or less peculiar, to each of these possible modes of excitation. Since, so far as is known, there is no morphological separation of function in these lowest forms of life, it is reasonably assumed that the single cell acts the part of " universal sense-organ," and that the advance to such complete differentiation of sense-organs as we find among the higher vertebrates has been a gradual advance. Numerous facts can now be adduced of the occurrence of " transitional " or " alternating " sense-organs among the lower forms of multi-cellular animals; organs, that is to say, which are normally responsive to two or more kinds of stimulus, and thus hold an intermediate position between the universal sense-organ of the Protozoa and the special sense-organ of the Mammalia. For example, a group of cells which would behave towards all stimuli impartially were they independent unicellular organ-isms become, as an organ in a multicellular organism, amenable only to mechanical or only to chemical stimuli,—become, that is to say, an organ of touch and of hearing, or an organ of taste and also of smell; until, finally, when differentiation is sufficiently advanced, the group ends by becoming exclusively the organ of one specified sense, touch or hearing in the one case, taste or smell in the other? Of course the imperfectly specialized sensations, say of the leech, and still more the wholly unspecialized sensations of the amoeba, cannot be regarded as blends of some or all of those which we are said to receive through our five senses. We must rather suppose that sensations at the outset corresponded very closely with the general vital action of stimuli as distinct from their action on specially differentiated sensory apparatus. Even now we are still aware of the general effects of light, heat, fresh air, food, &c., as invigorating or depressing quite apart from their specific qualities. Hence the frequent use of the term general or common sensibility (coenesthesis). But, though less definitely discriminated, the earlier, and what we call the lower, sensations are not any less concrete than the later and higher. They have been called general rather than specific, not because psychologically they lack any essential characteristic of sensation which those acquired later possess, but simply because physiologically they are not, like these, correlated to special sense-organs. But, short of resolving such sensations into combinations of one primordial modification of consciousness, if we could complexity conceive such, there are many interesting facts of which point clearly to a complexity that we can sensations, seldom . directly detect. Several of our supposed sensations of taste, e.g., are complicated with sensations of touch and smell: thus the pungency of pepper and the dryness of wine are tactual sensations, and their spicy flavours are really smells. How largely smells mingle with what we ordinarily take to be simply tastes is best brought home to us by a severe cold in the head, as this temporarily prevents the access of exhalations to the olfactory surfaces. The difference between the smooth feel of a polished surface and the roughness of one that is ' Cf. G. H. Lewes, Problems of Life and Mind (1879), vol. iii. pp. 250 sqq.; H. Spencer, Principles of Psychology, vol. i. § 6o. 2 Cf. W. A. Nagel, " Die Phylogenese specifischer Sinnesorgane," Bibliotheca zoologica (1894), pp. 1-42.unpolished, though to direct introspection an irresolvable difference of quality, is probably due to the fact that several nerve-terminations are excited in each case: where the sensation is one of smoothness all are stimulated equally; where it is one of roughness the ridges compress the nerve-ends more, and the hollows compress them less, than the level parts do. The most striking instance in point, however, is furnished by the differences in musical sounds, to which the name timbre is given. To the inattentive or uninstructed ear notes or " compound tones" appear to be only qualitatively diverse and not to be complexes of simple tones. Yet it is possible with attention and practice to distinguish these partial tones in a note produced on one instrument, a horn, say, and to recognize that they are different from those of the same note produced on a different instrument, for example, a violin. In like manner many persons believe that they can discriminate in certain colours, hence called mixed," the elementary colours of which they are held to be composed; red and yellow, for example, in orange, or blue and red in violet. But in so thinking they appear to be misled, partly by the resemblance that certainly exists between orange and red, on the one hand, and orange and yellow on the other, the two colours between which in the colour spectrum it invariably stands; and partly by the knowledge that, as a pigment, orange is obtainable by the mixture of red and yellow pigments; and so in the other cases. As we shall see later, however (§ 39), in this particular case of sensory continua, resemblance is no proof of complexity. Were it otherwise we should have to conclude that a given tone, since this also resembles the two between which it is intermediate, ought to be a blend of both; whereas, in point of fact, the tone d—though as regards pitch it has a certain resemblance to c and e, its neighbours on either side—differs widely from the chord c-e, which is made up of these. In all cases in which the psychical complexity of a sensation is beyond dispute the partial sensations are distinguished by discernible differences of extensity, and usually of intensity as well. Thus, if the skin be touched by the point of a hot or cold bradawl the temperature sensation has not the punctual character of the touch but seems rather to surround this as a sort of penumbra. Similarly, the ground-tone of a clang-complex has not only a greater intensity but also a greater extensity than any of the over-tones.' There is also in such cases a certain rivalry or antagonism between the complex as an unanalysed whole and the complex as analysed, and even between the several partial sensations after such analysis. In the absence of such direct evidence it is unwarrantable to infer psychical complexity from complexity in the physical stimuli, even when this is really present. In the case of pigment mixture, however, there is no such physical complexity as is vulgarly supposed. And it is worth noting that white light is physically the most complex of all, whereas the answering sensation is not only simple but probably the most primitive of all visual sensations. Every sensation within the fields of consciousness has sensibly some continuous duration and seems sensibly to admit of some continuous variation in intensity and ex- Quantitative tensity. But whether this quantitative continuity continuity. of presentational change is more than apparent has been questioned. Sensations of almost liminal intensity are found to fluctuate every few seconds, and, as already remarked, when the threshold of intensity is actually reached, they seem intermittently to appear and disappear, a fact which Hume long ago did not fail to notice. The results of numerous experiments, however, justify the conclusion that these variations are due primarily to oscillation of attention, and furnish so far no ground for the assumption that even the liminal sensation is discontinuous. But again we can only detect a difference of intensity when this is of finite amount and bears a certain constant ratio to the initial intensity with which it is compared —a fact commonly known as Weber's Law. But this imperfection in our power of discrimination is no proof that our sensations vary discontinuously; and not only is there no positive evidence in favour of such discontinuity, but it is altogether improbable on general grounds. Lastly, there is always more or less distinctness in the several nerve-endings as well as isolation of the nerve-fibres themselves. The skin, for example, when carefully explored, turns out to be a complex mosaic of so-called " spots," severally responding to stimulation by sensations of pressure, heat, cold and pain. But from this to argue that the extensity of a sensation is really a mere aggregate without any continuity is on a par with calling a lake a ' Cf. Stumpf, Tonpsychologie, ii. 58 seq. collection of pools because it is fed by separate streams. If it could be shown that in the brain as a whole there is no functional continuity a formidable psychophysical problem would no doubt arise. As regards the quality of sensations—the primitive sensation of sight appears to consist only of the single quality we call Quatnyot " light," a quality which ranges in intensity from Sensations. a dazzling brightness that becomes painful and blinding down to a zero of complete darkness; a limit which, however, is never completely attained, since the retina is always more or less internally stimulated—hence what is called the eye's own light (Eigenlicht). The first responses to light-stimulation seem to be very much on a par with our own to diffused heat or cold; some organisms seek the light and others shun it. As little as our temperature-sense yields us a perception of form does the light-sense at this level yield any. Not until the stage of visual spatial perception is reached and some discrimination of form is possible, do black and white attain the meaning they now have for us. An object can be visually perceived only when its colour or shade differs from that of the surrounding field; so far black as a " secondary quality " is on a par with colour, that is to say, when we are talking of things it may be called a quality. But there is still an important difference; in a light field many colours or shades may be distinguished, but in a dark field none. Though it is correct to speak of perceiving a black object, must we not then maintain that—so far as it is really black'—the object yields us directly no sensation? Similarly, the piper is said to " feel " the holes in his whistle when actually he only touches the solid metal in which they are pierced; or the soldier is said to hear the tattoo, though he has no auditory sensation of the silence intervening between successive taps on the drum. And it has yet to be shown that there is any more justification for speaking of visual sensations without luminosity. Meanwhile we must maintain that in absolute darkness we do not see black, since we do not see at all. No doubt we are prone to identify the two concepts darkness and blackness, for what we may call their sensory content is the same, viz. the absence of visual sensation. Whereas in nature the only diffused light we need consider is that emitted by the sun, the rays transmitted by the things about us vary in physical quality and in their effects upon protoplasm. As soon, therefore, as visual forms can be distinguished, a differentiation among light-sensations becomes obviously advantageous. The first colours to be differentiated were probably yellow and blue, or perhaps it would be truer to say " warm " colour and " cold " colour, upon which there followed a further differentiation of the warm colour into red and green.2 It is interesting to note that all possible sensations of colour constitute a specific continuum. We may represent it by a sphere, in which (a) the maximum of luminosity is at one pole and the minimum at the other; (b) the series of colours proper (red to violet and through purple back to red), constituting a closed line, are located round the equator or in zones parallel to it, according to shade; and (c) the amount of saturation (or absence of white) for any given zone of illumination increases with distance from the axis. In dealing with the quality of auditory sensations we have to distinguish between the simple sensations called tones and the sensation-complexes, either clangs or noises, which result from their combination. Simple tones also constitute a qualitative continuum, but it has only one dimension, their so-called " pitch "; this may be represented by a straight line ranging between two more or less indefinite extremes. If intensity, that is to say loudness, is taken into account, we have of course a continuum of two dimensions. The tone-continuum is also universally regarded as steadily diminishing in massiveness or extensity as the pitch rises. And, in fact, as we approach the lower ' As a matter of fact there are no objects absolutely black, none that are devoid of all lustre and completely absorbent of light. But this does not affect the argument. 2 It is assumed that the physiological differentiation of the retina has advanced from the centre,where vision is most distinct, towards the margin where it is least so; and it is found that stimulation of the margin yields none but achromatic sensations, stimulation of a certain intermediate zone only sensations of yellow or blue, and central stimulation alone sensations of every hue. Further, total colour-blindness is extremely rare, whereas red-green colour-blindness is comparatively common.limit, the so-called deep or grave tones become less " even," till at length distinct, more or less pervasive, tremors are felt rather than heard as distinct impulses on the ear-drum. The so-called high or acute tones again, as we approach their limit, are accompanied by tactual, often more or less painful, sensations, as if the ear were pierced by a fine needle. This connexion of auditory with tactual sensations confirms the independent evidence of biology pointing to an original differentiation of sound from touch. The special characteristics of tone-complexes, whether clangs or noises, are due to the remarkable analytic power which belongs to the sense of hearing. Two colours cannot be simultaneously presented unless they are differently localized, but several tones may form one complex whole within which they, as " partial " tones, are distinguish-able, though spatially undifferentiated. Unlike the higher senses of sight and hearing, the lower senses of touch, taste, smell, &c., do not constitute qualitative continua. Temperatures may indeed be represented as ranging in opposite directions, i.e. through heat or through cold, between a zero of no sensation and the organic sensations due to the destructive action of both extremes, heat and cold alike. But the continuity in this case is intensive rather than qualitative. Tastes fall into the four isolated qualities known as sweet, sour, bitter, saline; but smells hardly admit of classification at all.. Sensations of touch and sight have in a pre-eminent degree a certain peculiar continuity which differentiations of extensity entail, and which we shall have presently to consider further under the title of local signs. The various sensations classed together as organic, hunger, thirst, physical pain, &c., are left to the physiologist to describe. Our motor presentations contrast with the sensory by their want of striking qualitative differences. They are divided into two groups: (a) motor presentations proper and movements (b) auxilio-motor of kinaesthetic presentations. The former answer to our " feelings of muscular effort " or " feelings of innervation." The latter are those presentations due to the straining of tendons, stretching and flexing of the skin, and the like, by which the healthy man knows that his efforts to move are followed by movement, and so knows the position of his body and limbs. It is owing to the absence of these presentations that the anaesthetic patient cannot directly tell whether his efforts are .effectual or not, nor in what position his limbs have been placed by movements from without. Thus under normal circumstances motor presentations are always accompanied by auxilio-motor; but in disease and in passive movements they are separated and their distinctness thus made manifest. Originally we may suppose kinaesthetic presentations to have formed one imperfectly differentiated continuum, but now, as with sensations, they have become a collection of special continua, viz. the groups of movements possible to each limb and certain combinations of these movements. But whereas kinaesthetic presentations were commonly allowed to be purely sensory, the concomitants of centripetal excitations—hence the older name of " muscular or sixth sense " applied to them by Sir Charles Bell, Weber, Sir William Hamilton and others—concerning motor presentations proper, a very different view, first tentatively advanced by the great physiologist Johannes Muller, and adopted by Helmholtz, Wundt, and especially by Bain, long prevailed. It is, however, now generally discredited, if not completely overthrown.' According to this view, " the characteristic feeling of exerted force " must be regarded, Bain maintained, " not as arising from an inward transmission . . . but as the concomitant of the outgoing current by which the muscles are stimulated to act " (op. cit. p. 79). The necessity for this assumption has certainly not been established on physiological grounds, nor apparently did Bain rely primarily on these; for at the very outset of his discussion we find him saying " that action is a more intimate and inseparable property of our constitution than any of our sensations, and enters as a component part into every one of our senses " (op. cit. p. 59). But this important psychological truth is affirmed as strenuously by some, at any rate (e.g. Professor James) of Bain's opponents as it was by Bain himself. Unhappily many, under the same psychophysical ' Cf. Bastian, The Brain as an Organ of Mind (188o), pp. 691 sqq.; Ferrier, The Functions of the Brain (1886), and ed. pp. 382 sqq.; James, Principles of Psychology (1890), eh xxvi. bias and so induced, like the upholders of this innervation theory, to look for evidence of subjective activity in the wrong place, have been led to doubt or to deny the reality of this activity altogether. In fact, this theory, while it lasted, tended to sustain an undue separation of so-called " sensory " from so-called " motor " presentations, as if living experience were literally an alternation of two independent states, one wholly passive and the other wholly active, corresponding to the anatomical distinction of organs of sense and organs of movement. The subject of experience or Ego does not pass to and fro between a sensorium commune or intelligence department and a motorium commune or executive, is not in successive intervals receptive and active, still less always passive, but rather always actively en rapport with an active Non-Ego, commonly called the External World. Perception. 17. In treating apart of the differentiation of our sensory and motor continua, as resulting merely in a number of dis-Mentai syn- tinguishable sensations and movements, we have thesis or been compelled by the exigencies of exposition Integration. to leave out of sight another process which really advances pari passe with this differentiation, viz. the integration or synthesis of these proximately elementary presentations into those complex presentations which are called percepts, intuitions, sensori-motor reactions and the like. It is, of course, not to be supposed that in the evolution of mind any creature attained to such variety of distinct sensations and movements as a human being possesses without making even the first step towards building up this material into the most rudimentary knowledge and action. On the contrary, there is every reason to think, as has been said already incidentally, that further differentiation was helped by previous integration, that perception prepared the way for distincter sensations, and purposive action for more various movements. This process of synthesis, which is in the truest sense a psychical process, deserves some general consideration before we proceed to the several complexes that result from it. Most complexes, certainly the most important, are consequences of that principle of subjective selection whereby interesting sensations lead through the intervention of feeling to movements; and the movements that turn out to subserve such interest come to have a share in it. In this way—which we need not stay to examine more closely now—it happens that a certain sensation, comparatively intense, and a certain movement, definite enough to control that sensation, engage attention, to the more or less complete exclusion of the other less intense sensations and more diffused movements that accompany them. Apart from this intervention of controlling movements, the presentation-continuum, however much differentiated, would remain for all purposes of knowledge little better than the disconnected manifold for which Kant took it. At the same time it is to be remembered that the subject obtains command of particular movements out of all the mass involved in emotional expression only because such movements prove on occurrence adapted to control certain sensations. A long process, in which natural selection probably played the chief part at the outset—subjective selection becoming more prominent as the process advanced—must have been necessary to secure as much purposive movement as even a worm displays. We must look to subjective interest to explain, so far as psychological ex-planation is possible, those syntheses of motor and sensory presentations which we call spatial perception and the in-tuitions of material things. For example, some of the earliest lessons of this kind seem to be acquired as we may presently see, in the process of exploring the body by means of the limbs, —a process for which grounds in subjective interest can obviously never be wanting. Perception sometimes means only the recognition of a sen- sation or movement as distinct from its original presentation, thus implying the more or less definite revival of certain residua of past experience which re- sembled the present. More frequently it is used as the equivalent of what has been otherwise called the " localization and projection " of sensations—that is to say, of sensations apprehended either as affections of some part of our own body regarded as extended or as states of some foreign body beyond it. According to a former usage, strictly taken, there might be perception without any spatial presentation at all; a sensation that had been attended to a few times might be perceived as familiar. According to the latter, an entirely new sensation, provided it were complicated with motor experiences in the way required for its localization or projection, would be perceived. But as a matter of fact actual perception probably invariably includes both cases: impressions which we recognize we also localize or project, and impressions which are localized or projected are never entirely new—they are, at least, perceived as sounds or colours or aches, &c. It will, however, frequently happen that we are specially concerned with only one side of the whole process, as is the case with a tea-taster or a colour-mixer on the one hand, or, on the other, with the patient who is perplexed to decide whether what he sees and hears is " subjective," or whether it is " real." But there is still a distinction called for: perception as we now know it involves not only recognition (or assimilation) and localization, or " spatial reference," as it is not very happily termed, but it usually involves " objective reference " as well. We may perceive sound or light without any presentation of that which sounds or shines; but none the less we do not regard such sound or light as merely the object of our attention, as having only immanent existence, but as the quality or .change or state of a thing, an object distinct not only from the subject attending but from all presentations whatever to which it attends. Here again the actual separation is impossible, because this factor in perception has been so intertwined throughout our mental development with the other two. Still a careful psychological analysis will show that such " reification," as we might almost call it, has depended on special circumstances, which we can at any rate conceive absent. These special circumstances are briefly the constant conjunctions and successions of impressions, for which psychology can give no reason, and the constant movements to which they prompt. Thus we receive together, e.g. those impressions we now recognize as severally the scent, colour, and " feel " of the rose we pluck and handle. We might call each a " percept," and the whole a " complex percept." But there is more in such a complex than a sum of partial percepts; there is the apprehension or intuition of the rose as a thing having this scent, colour and texture. We have, then, under perception to consider (a) the recognition and (b) the localization of impressions, and (c) the intuition of things. 18. The range of the terms recognition or assimilation of impressions is wide: between the simplest mental process they may be supposed to denote and the most complex Assimilathere is a great difference. The penguin that tion of watched unmoved the first landing of man upon its Impressions. lonely rock becomes as wild and wary as more civilized fowl after two or three visits from its molester: it then recognizes that featherless biped. His friends at home also recognize him though altered by years of peril and exposure. In the latter case some trick of voice or manner, some " striking" feature, calls up and sustains a crowd of memories of the traveller in the past—events leading on to the present scene. The two recognitions are widely different, and it is from states of mind more like the latter than the former that psychologists have usually drawn their description of perception. At the outset, they say, we have a primary presentation or impression P, and after sundry repetitions there remains a mass or a series of P residua, plp2p3 . . . ; perception ensues when, sooner or later, P,, " calls up " and associates itself with these representations or ideas. Much of our later perception, and especially when we are at all interested, awakens, no doubt, both distinct memories and distinct expectations; but, since these imply previous perceptions, it is obvious that the earliest form of re-cognition, or, as we might better call it, assimilation, must be free from such complications, can have nothing in it answering to the overt judgment, P. is a P. Assimilation involves retentiveness and differentiation, as we have seen, and prepares the way for re-presentation; but in itself there is no confronting Meaning of Perception. the new with the old, no determination of likeness, and no subsequent classification. The pure sensation we may regard as a psychological myth; and the simple image, or such sensation revived, seems equally mythical, as we may see later on. The nth sensation is not like the first: it is a change in a presentation-continuum that has itself been changed by those pre-ceding; and it cannot with any propriety be said to reproduce these past sensations, for they never had the individuality which such reproduction implies. Nor does it associate with images like itself, since where there is association there must first have been distinctness, and what can be associated can also, for some good time at least, be dissociated. ig. To treat of the localization of impressions is really to give an account of the steps by which the psychological Localization individual comes to a knowledge of space. At of Impress the outset of such an inquiry it seems desirable first signs. of all to make plain what lies within our purview, and what does not, lest we disturb the peace of those who, con-founding philosophy and psychology, are ever eager to fight for or against the a priori character of this element of knowledge. That space is a priori in the epistemological sense it is no concern of the psychologist either to assert or to deny. Psycho-logically a priori or original in such sense that it has been either actually or potentially an element in all presentation from the very beginning it certainly is not. It will help to make this matter clearer if we distinguish what philosophers frequently confuse, viz. the concrete spatial experiences, constituting actual localization for the individual, and the abstract concept of space, generalized from what is found to be common in such experiences. A gannet's mind " possessed of " a philosopher, if such a conceit may be allowed, would certainly afford its tenant very different spatial experiences from those he might share if he took up his quarters in a mole. So, any one who has revisited in after years a place from which he had been absent since childhood knows how largely a " personal equation," as it were, enters into his spatial perceptions. Or the same truth may be brought home to him if, walking with a friend more athletic than himself, they come upon a ditch, which both know to be twelve feet wide, but which the one feels he can clear by a jump and the other feels he cannot. In the concrete " up " is much more than a different direction from " along." The hen-harrier, which cannot soar, is indifferent to a quarry a hundred feet above it—to which the peregrine, built for soaring, would at once give chase—but is on the alert as soon as it descries prey of the same apparent magnitude, but upon the ground. Similarly, in the concrete, the body is the origin or datum to which all positions are referred, and such positions differ not merely quantitatively but qualitatively. Moreover, our various bodily movements and their combinations constitute a net-work of co-ordinates, qualitatively distinguishable but geometrically, so to put it, both redundant and incomplete. It is a long way from these facts of perception, which the brutes share with us, to that scientific concept of space as having three dimensions and no qualitative differences which we have elaborated by the aid of thought and language, and which reason may see to be the logical presupposition of what in the order of mental development has chronologically preceded it. That the experience of space is not psychologically original seems obvious —quite apart from any successful explanation of its origin—from the mere consideration of its complexity. Thus we must have a plurality of objects—A out of B, B beside C, distant from D, and so on; and these relations of externality, juxtaposition, and size or distance imply further specialization; for with a mere plurality of objects we have not straightway spatial differences. Juxtaposition, e.g. is only possible when the related objects form a continuum; but, again, not any continuity is extensive. Now how has this complexity come about? The first condition of spatial experience seems to lie in what has been noted above (§ rr) as the extensity of sensation. This much, we may allow is original; for the longer we reflect the more clearly we see that no combination or association of sensations varying only in intensity and quality, not even if motor presentations are added, will account for this space-element in our perceptions. A series of touches a, b, c, d may be combined with a series of movements m,, m2, m3, m4; both series may be reversed; and finally the touches may be presented simultaneously. In this way we can attain the knowledge of the coexistence of objects that have a certain quasi-distance between them, and such experience is an important element in our perception of space; but it is not the whole of it. For, as has been already remarked by critics of the associationist psychology, we have an experience very similar to this in singing and hearing musical notes or the chromatic scale. The most elaborate attempt to get extensity out of succession and coexistence is that of Herbert Spencer. He has done, perhaps, all that can be done, and only to make it the more plain that the entire procedure is a uvrepov rrpbrepov. We do not first experience a succession of touches or of retinal excitations by means of movements, and then, when these impressions are simultaneously presented, regard them as extensive, because they are associated with or symbolize the original series of movements; but, before and apart from movement altogether, we experience that massiveness or extensity of impressions in which movements enable us to find positions, and also to measure.' But it will be objected, perhaps not with-out impatience, that this amounts to the monstrous absurdity of making the contents of consciousness extended. The edge of this objection will best be turned by rendering the concept of extensity more precise. Thus, suppose a postage stamp pasted on the back of the hand; we have in consequence a certain sensation. If another be added beside it, the new experience would not be adequately described by merely saying we have a greater quantity of sensation, for intensity involves quantity, and increased intensity is not what is meant. For a sensation of a certain intensity, say a sensation of red, cannot be changed into one having two qualities, red and blue, leaving the intensity unchanged; but with extensity this change is possible. For one of the postage stamps a piece of wet cloth of the same size might be substituted and the massiveness of the compound sensation remain very much the same. Intensity belongs to what may be called graded quantity: it admits of increment or decrement, but is not a sum of parts. Extensity, on the other hand, does imply plurality: we might call it latent or merged plurality or a " ground " of plurality, inasmuch as to say that a single presentation has massiveness is to say that a portion of the presentation-continuum at the moment undifferentiated is capable of differentiation. Attributing this property of extensity to the presentation-continuum as a whole, we may call the relation of any particular sensation to this larger whole its local sign, and can see Local Signs. that, so long as the extensity of a presentation admits of diminution without the presentation becoming nil such presentation either has or may have two or more local signs—its parts, taken separately, though identical in quality and intensity, having a different relation to the whole. Such difference of relation must be regarded fundamentally as a ground or possibility of distinctness of sign—whether as being the ground or possibility of different complexes or otherwise—rather than as being from the beginning such an overt difference as the term " local sign," when used by Lotze, is meant to imply.2 From We are ever in danger of exaggerating the competence of a new discovery; and the associationists seem to have fallen into this mistake, not only in the use they have made of the concept of association in psychology in general, but in the stress they have laid upon the fact of movement when explaining our space-perceptions in particular. Indeed, both ideas have here conspired against them—association in keeping up the notion that we have only to deal with a plurality of discrete impressions, and movement in keeping to the front the idea of sequence. Mill's Examination of Hamilton (3rd ed., p. 266 seq.) surely ought to convince us that, unless we are prepared to say, as Mill seems to do, " that the idea of space is at bottom one of time " (p. 276), we must admit the inadequacy of our experience of movement to explain the origin of it. 2 To illustrate what is meant by different complexes it will be enough to refer to the psychological implications of the fact that scarcely two portions of the sensitive surface of the human body are anatomically alike. Not only in the distribution and character of Extensity. this point of view we may say that more partial presentations are concerned in the sensation corresponding to two stamps than in that corresponding to one. The fact that these partial presentations, though identical in quality and intensity, on the one hand are not wholly identical, and on the other are presented only as a quantity and not as a plurality, is explained by the distinctness along with the continuity of their local signs. Assuming that to every distinguishable part of the body there corresponds a local sign, we may allow that at any moment only a certain portion of this continuum is definitely within the field of consciousness; but no one will maintain that a part of one hand is ever felt as continuous with part of the other or with part of the face. Local signs have thus an invariable relation to each other: two continuous signs are not one day coincident and the next widely separate.' This last fact is only implied in the mere massiveness of a sensation in so far as this admits of differentiation into local signs. We have, then, when the differentiation is accomplished, a plurality of presentations constituting an extensive continuum, presented simultaneously, and having certain fixed and invariable relations to each other. Of such experience the typical case is that of passive touch, though the other senses exemplify it. It must be allowed that' our concept of space in like manner involves a fixed continuity of positions; but then it involves, further, the possibility of movement. Now in the continuum of local signs there is nothing whatever of this; we might call this continuum an implicit plen_tm. It only becomes the presentation of oecupied space after its several local signs are complicated in an orderly way with active touches, when in fact we have experienced the contrast of movements with contact and movements without, i.e. in vacuo. It is quite true that we cannot now think of this plenum except as a space, because we cannot divest ourselves of these motor experiences by which we have explored it. We can, how-ever, form some idea of the difference between the perception of space and this one element in the perception by contrasting massive internal sensations with massive superficial ones, or the general sensation of the body as " an animated organism " with our perception of it as extended. Or we may express the difference by remarking that extension implies the distinction of here and there, while extensity rather suggests ubiquity. It must seem strange, if this conception of extensity is essential to a psychological theory of space, that it has escaped notice so long. The reason may be that in investigations into the origin of our knowledge of space it was always the concept of space and not our concrete space percepts that came up for examination. Now in space as we conceive it one position is distinguishable from another solely by its co-ordinates, i.e. by the magnitude and signs of certain lines and angles, as referred to a certain datum, position or origin; - and these elements our motor experiences seem fully to explain. But on reflection we ought, surely, to be puzzled by the question, how these coexistent positions could be known before those movements were made which constitute them different positions. The link we thus suspect to be missing is supplied by the more concrete experiences we obtain from our own body, in which two positions have a qualitative difference or " local colour " independently of move- ment. True, such positions would not be known as spatial without movement; but neither would the movement be known as spatial had those positions no other difference than such asarises from movement. In a balloon drifting steadily in a fog we should have no more experience of change of position than if it hung becalmed and still. We may now consider the part which movement plays in elaborating the presentations of this dimensionless continuum into percepts of space. In so doing we must bear in mind that while this continuum implies the incopresentability of two impressions having the same local sign, it allows not only of the presentation of sensations of varying massiveness, but also of a sensation involving the whole continuum simultaneously, as in Bain's classic example of the warm bath. As regards the motor element itself, the first point of importance is the incopresentability and invariability of a successive series of auxiliomotor or kinaesthetic presentations, P1, P2, P3, P4. PI cannot be presented along with P2, and from P4 it is impossible to reach Pi again save through P3 and P2. Such a series, taken alone, could afford us, it is evident, nothing but the knowledge of an invariable sequence of impressions which it was in our own power to produce. Calling the series of P's " positional signs," the contrast between them and local signs is obvious. Both are invariable, but succession characterizes the one, simultaneity the other; the one yields potential position without place, the other potential place (roiros) without position; hence we call them both merely signs .2 But in the course of the movements necessary to the exploration of the body—probably our earliest lesson in spatial perception—these positional signs receive a new significance from the active and passive touches that accompany them, just as they impart to these last a significance they could never have alone. It is only in the resulting complex that we have the presentations of actual position and of spatial magnitude. For space, though conceived as a coexistent continuum, excludes the notion of omnipresence or ubiquity; two positions la and lg must coexist, but they are not strictly distinct positions so long as we conceive ourselves present in the same sense in both. But, if Fa and Fg are, e.g. two impressions produced by compass points touching two different spots as la and l8 on the hand or arm, and we place a finger upon la and move it to lg, experiencing thereby the series P2, P3, P4, this series constitutes Id and lg into positions and also invests Fa and Fg with a relation not of mere distinctness asroirot but of definite distance. The resulting complex perhaps admits of symbolization as follows: FjF,FeFdFjFfF,FhFk Tttt P1p.PaP4 Here the first line represents a portion of the tactual continuum, Fd and F, being distinct " feels," if we may so say, or passive touches presented along with the fainter sensations of the continuum as a whole, which the general " body-sense " involves; T stands for the active touch of the exploring finger and Pi for the corresponding kinaesthetic sensation regarded as " positional sign "; the rest of the succession, as not actually present at this stage but capable of revival from past explorations, is symbolized by the t i t and p2PaP4. When the series of movements is accompanied by active touches without passive there arises the distinction between one's own body and foreign bodies; when the initial movement of a series is accompanied by both active and passive touches, the final movement by active touches only, and the intermediate movements are unaccompanied by either, we get the further presentation of empty space lying between us and them—but only when by frequent experience of contacts along with those intermediate movements we have come to know all movement as not only succession but change of position. Thus active touches come at length to be projected, passive touches alone being localized in the stricter sense. But in actual fact, of course, the localization of one impression is not perfected before that of another is begun, and we must take care lest our necessarily meagre exposition give rise to the • mistaken notion 2 Thus a place may be known topographically without its position being known geographically, and vice versa. the nerve-endings but in the variety of the underlying parts—in one place bone, in another fatty tissue, in others tendons or muscles variously arranged—we find ample ground for diversity in " the local colouring " of sensations. And comparative zoology helps us to see how such diversity has been developed as external impressions and the answering movements have gradually differentiated an organism originally almost homogeneous and symmetrical. Between one point and another on the surface of a sphere there is no ground of difference ; but this is no longer true if the sphere revolves round a fixed axis, still less if it also runs in one direction along its axis. ' The improvements in the sensibility of our " spatial sense" consequent on practice, its variations under the action of drugs, &c., are obviously no real contradiction to this; on the contrary, such facts are all in favour of making extensity a distinct factor in our space experience and one more fundamental than that of movement. Positional signs. that localizing an impression consists wholly and solely in performing or imaging the particular movements necessary to add active touches to a group of passive impressions. That this cannot suffice is evident merely from the consideration that a single position out of relation to all other positions is a contra-diction. Localization, though it depends on many special experiences of the kind described, is not like an artificial product which is completed a part at a time, but is essentially a growth, its several constituents advancing together in definiteness and interconnexion. So far has this development advanced that we do not even imagine the special movements which the localization of an impression implies, that is to say, they are no longer distinctly represented as they would be if we definitely intended to make them: the past experiences are " retained," but too much blended in the mere perception to be appropriately spoken of as remembered or imaged. A propos of this almost instinctive character of even our earliest spatial percepts it will be appropriate to animadvert on a misleading implication in the current use of such terms as " localization," " projection," " bodily reference," " spatial reference " and the like. The implication is that external space, or the body as extended, is in some sort presented or supposed apart from the localization, projection or reference of impressions to such space. That it may be possible to put a book in its place on a shelf there must be (I) the book, and (2), distinct and apart from it, the place on the shelf. But in the evolution of our spatial experience impressions and positions are not thus presented apart. We can have, or at least we can suppose, an impression which is recognized without being localized as has been already said; but if it is localized this means that a more complex presentation is formed by the addition of new elements, not that a second distinct object is presented and some indescribable connexion established between the impression and it, still less that the impression is referred to something not strictly presented at all. The truth is that the body as extended is from the psychological point of view not perceived at all apart from localized impressions. In like manner impressions projected (or the absence of impressions projected) constitute all that is perceived as the occupied (or unoccupied) space beyond. It is not till a much later stage, after many varying experiences of different impressions similarly localized or projected, that even the mere materials are present for the formation of such an abstract concept of space as " spatial reference " implies.' Psychologists, being themselves at this later stage, are apt to commit the oversight of introducing it into the earlier stage which they have to expound. 20. In a complex percept, such as that of an orange or a piece of wax, may be distinguished the following points concerning which psychology may be expected to give an account: (a) the object's reality, (b) its solidity or occupation of space, (c) its unity and complexity, (d) its permanence, or rather its continuity in time and (e) its substantiality and the connexion of its attributes and powers. Though, in fact, these items are most intimately blended, our exposition will be clearer if we consider each for a moment apart. a. The terms actuality and reality have each more than one meaning. Thus what is real, in the sense of material, is opposed acruatHy or to what is mental; as the existent or actual it is Reality opposed to the non-existent; and again, what is actual is distinguished from what is possible or necessary. But here both terms, with a certain shade of difference, in so far as actual is more appropriate to movements and events, are used, in antithesis to whatever is ideal or represented, for what is sense-given or presented. This seems at least their primary psychological meaning; and it is the one most in vogue in English philosophy at any rate, over-tinged as that is with psycho-logy.' Any examination of this characteristic will be best deferred till we come to deal with ideation generally (see § 21 below). Meanwhile it may suffice to remark that reality or actuality is not a single distinct element added to the others which enter into the complex presentation we call a thing, ' Cf. on this point Poincare, La Science et l'hypothese, pp. 74 sqq. 2 Thus Locke says, " Our simple ideas [i.e. presentations or impressions, as we should now say] are all real. ..and not fictions at pleasure; for the mind . . . can make to itself no simple idea more than what it has received " (Essay, ii. 30, 2). And Berkeley says, " The ideas imprinted on the senses by the Author of Nature are called real things; and those excited in the imagination, being less regular, vivid and constant, are more properly termed ideas or images of things, which they copy or represent " (Prin. of Hum. Know., pt. i. § 33)as colour or solidity may be. Neither is it a special relation among these elements, like that of substance and attribute, for example. In these respects the real and the ideal, the actual and the possible, are alike; all the elements or qualities within the complex, and all the relations of those elements to each other, are the same in the rose represented as in the presented rose. The difference turns not upon what these elements are, regarded as qualities or relations presented or represented, but upon whatever it is that distinguishes the presentation from the representation of any given qualities or relations. Now this distinction, as we shall see, depends partly upon the relation of such complex presentation to other presentations in consciousness with it, partly upon its relation as a presentation to the subject whose presentation it is. In this respect we find a difference, not only between the simple qualities, such as cold, hard, red and sweet in strawberry ice, e.g. as presented and as represented, but also, though less conspicuously, in the spatial, and even the temporal, relations which enter into our intuition as distinct from our imagination of it. So then, reality or actuality is not strictly an item by itself, but a characteristic of all the items that follow. b. In the so-called physical solidity or impenetrability of things our properly motor presentations or feelings of effort or innervation " come specially into play. They impenetraare not entirely absent in those movements of biuty. exploration by which we attain a knowledge of space; but it is when these movements are definitely resisted, ' or are only possible by increased effort, that we reach the full meaning of body as that which occupies space. Heat and cold, light and sound, the natural man regards as real, and by and by perhaps as due to the powers of things known or unknown, but not as themselves things. At the outset things are all corporeal like his own body, the first and archetypal thing, that is to say: things are intuited only when touch is accompanied by pressure; and, though at a later stage passive touch without pressure may suffice, this is only because pressures depending on a subjective initiative, i.e. on voluntary muscular exertion, have been previously experienced. It is of more than psychological interest to remark how the primordial factor in materiality is thus due to the projection of a subjectively determined reaction to that action of a not-self of which sense-impressions consist—an action of the not-self which, of course, is not known as such till this projection of the subjective reaction has taken place. Still we must remember that accompanying sense-impressions are a condition of its projection: muscular effort without simultaneous sensations of contact would not yield the distinct presentation of something resistant occupying the space into which we have moved and would move again. Nay more, it is in the highest degree an essential circumstance in this experience that muscular effort, though subjectively initiated, is still only possible when there is contact with something that, as it seems, is making an effort the counterpart of our own. But this something is so far no more than thing-stuff; without the elements next to be considered our psychological individual would fall short of the complete intuition of distinct things. c. The remaining important factors in the psychological constitution of things might be described in general terms as the time-relations of their components. Such rela- tions are themselves in no way psychologically deter-Unity and Complexity. mined; impressions recur with a certain order or want of order quite independently of the subject's interest or of any psychological principles of synthesis or association whatever. It is essential that impressions should recur, and recur as they have previously occurred, if knowledge is ever to begin; out of a continual chaos of sensation, all matter and no form, such as some philosophers describe, nothing but chaos could result. But a flux of impressions having this real or sense-given order will not suffice; there must be also attention to and retention of the order, and these indispensable processes at least are psychological. But for its familiarity we should marvel at the fact that out of the variety of impressions simultaneously presented we do Intuition of Things. not instantly group together all the sounds and all the colours, all the touches and all the smells; but, dividing what is given together, single out a certain sound or smell as belonging together with a certain colour and feel, similarly singled out from the rest, to what we call one thing. We might wonder, too —those at least who have made so much of association by similarity ought to wonder—that, say, the white of snow calls up directly, not other shades of white or other colours, but the expectation of cold or of powdery softness. The first step in this process has been the simultaneous projection into the same occupied space of the several impressions which we thus come to regard as the qualities of the body filling it. Yet such simultaneous and coincident projection would avail but little unless the constituent impressions were again and again repeated in like order so as to prompt anew the same grouping, and unless, further, this constancy in the one group was present along with changes in other groups and in the general field. There is nothing in its first experience to tell the infant that the song of the bird does not inhere in the hawthorn whence the notes proceed, but that the fragrance of the mayflower does. It is only where a group, as a whole, has been found to change its position relatively to other groups, and—apart from casual relations—to be independent of changes of position among them, that such complexes can become distinct unities and yield a world of things. Again, because things are so often a world within themselves, their several parts or members not only having distinguishing qualities but moving and changing with more or less independence of the rest, it comes about that what is from one point of view one thing becomes from another point of view several—like a tree with its separable branches and fruits, for example. Wherein then, more precisely, does the unity of a thing consist? This question, so far as it here admits of answer, carries us over to temporal continuity. d. Amidst all the change above described there is one thing comparatively fixed: our own body is both constant as a group and a constant item in every field of groups; and not Temporal onl so but it is beyond all other things an object continuity. y of continual and peculiar interest, inasmuch as our earliest pleasures and pains depend solely upon it and what affects it. The body becomes, in fact, the earliest form of self, the first datum for our later conceptions of permanence and individuality. A continuity like that of self is then transferred to other bodies which resemble our own, so far as our direct experience goes, in passing continuously from place to place and undergoing only partial and gradual changes of form and quality. As we have existed—or, more exactly, as the body has been continuously presented—during the interval between two encounters with some other recognized body, so this is regarded as having continuously existed during its absence from us. However permanent we suppose the conscious subject to be, it is hard to see how, without the continuous presentation to if of such a group as the bodily self, we should ever be prompted to resolve the discontinuous presentations of external things into a continuity of existence. It might be said: Since the second presentation of a particular group would, by the mere workings of psychical laws, coalesce with the image of the first, this coalescence would suffice to " generate " the concept. of continued existence. But such assimilation is only the ground of an intellectual identification and furnishes no motive, one way or the other, for real identification: between a second presentation of A and the presentation at different times of two A's there is so far no difference. Real identity no more involves exact similarity than exact similarity involves sameness of things; on the contrary, we are wont to find the same thing alter with time, so that exact similarity after an interval, so far from suggesting one thing, is often the surest proof that there are two concerned. Of such real identity, then, it would seem we must have direct experience; and we have it in the continuous presentation of the bodily self; apart from this it could not be " generated " by association among changing presentations. Ot her bodies being in the first instance personified, that then is regarded as one thing—from whatever point of view we look at it, whether as part of a larger thing or as itself compounded of such parts—which has had one beginning in time. But what is it that has thus a beginning and continues indefinitely? This leads to our last point. e. So far we have been concerned only with the combination of sensory and motor presentations into groups and with the differentiation of group from group; the relations to each other of the constituents of each group still a 1 antillty. for the most part remain. To these relations in the main must be referred the correlative concepts of substance and attribute, the distinction in substances of qualities and powers, of primary qualities and secondary, and the like?. Of all the constituents of things only one is universally present, that above described as physical solidity, which presents itself according to circumstances as impenetrability, resistance or weight. Things differing in temperature, colour, taste and smell agree in resisting compression, in filling space. Because of this quality we regard the wind as a thing, though it has neither shape nor colour, while a shadow, though it has both but not resistance, is the very type of nothingness. This constituent is invariable, while other qualities are either absent or change—form altering, colour disappearing with light, sound and smells intermitting. Many of the other qualities—colour, temperature, sound, smell—increase in intensity if we advance till we touch a body occupying space; with the same movement too its visual magnitude varies. At the moment of contact an unvarying tactual magnitude is ascertained, while the other qualities and the visual magnitude reach a fixed maximum; then first it becomes possible by effort to change or attempt to change the position and form of what we apprehend. This tangible plenum we thenceforth regard as the seat and source of all the qualities we project into it. In other words, that which occupies space is psychologically the substantial; the other real constituents are but its properties or attributes, the marks or manifestations which lead us to expect its presence. Imagination or Ideation? 21. Before the intuition of things has reached a stage so complete and definite as that just described, imagination or ideation as distinct from perception has well begun. In I to the consideration of this higher form of and passing Ideas. mental life we must endeavour first of all analytically to distinguish the two as precisely as may be and then to trace the gradual development of the higher. To begin, it is very questionable whether Hume was right in applying Locke's distinction of simple and complex to ideas in the narrower sense as well as to impressions. " That idea of red," says Hume, " which we form in the dark and that impression which strikes our eyes in the sunshine differ only in degree, not in nature." 3 But what he seems to have overlooked is that, whereas we may have a mere sensation red, we can only have an image or representation of a red thing or a red form, i.e of red in some way ideally projected' or intuited. In other words, there are no ideas—though there are concepts—answering to simple or isolated impressions. The synthesis which has taken place in the evolution of the percept can olily partially fail in the idea, and never so far as to leave us with a chaotic " manifold " of mere sensational remnants. On the contrary, we find that in " constructive imagination " a new kind of effort is often requisite in order partially to dissociate these representational complexes as a preliminary to new combinations. But it is doubtful whether the results of such an analysis are ever the ultimate elements of the percept, that is, merely isolated impressions in a fainter form. We may now try to ascertain further the characteristic marks which distinguish what is imaged from what is perceived. The distinction between the thing and its properties is one that might be more fully treated under the head of " Thought and Conception." Still, inasmuch as the material warrant for these concepts is contained more or less implicity in our percepts, some consideration of it is in place here. z Ideation—" a word of my own coining," says James Mill. 3 Treatise of Human Nature, bk. i. pt. i. § I. The most obvious difference is that which Hume called I " the force or liveliness " of primary presentations as compared Character- with secondary presentations. But what exactly istks of are we to understand by this somewhat figurative Ideas. language ? A simple difference of intensity cannot be all that is meant, for--though we may be momentarily confused—we can perfectly well distinguish the faintest impression from an image; moreover, we can reproduce such faintest impressions in idea. The whole subject of the intensity of representations awaits investigation. Between moonlight and sunlight or between midday and dawn we can discriminate many grades of intensity; but it does not appear that there is any corresponding variation of intensity between them when they are not seen but imagined. Many persons suppose they can imagine a waxing or a waning sound or the gradual abatement of an intense pain; but what really happens in such cases is probably not a rise and fall in the intensity of a single representation, but a change in the complex represented. In the primary presentation there has been a change of quality along with change of intensity, and not only so, but most frequently a change in the muscular adaptations of the sense-organs too, to say nothing of organic sensations accompanying these changes. A representation of some or all of these attendants is perhaps what takes place when variations of intensity are supposed to be reproduced. Again, hallucinations are often described as abnormally intense images which simply, by reason of their intensity, are mistaken for percepts. But such statement, though supported by very high authority, is almost certainly false, and would probably never have been made if physiological and epistemological considerations had been excluded as they ought to have been. Hallucinations, when carefully examined, seem just as much as percepts to contain among their constituents some primary presentation—either a so-called subjective sensation of sight and hearing or some organic sensation due to deranged circulation or secretion. Intensity alone, then, will not suffice to discriminate between impressions and images. What we may call superior steadiness is perhaps a more constant and not less striking characteristic of percepts. Ideas are not only in a continual flux, but even when we attempt forcibly to detain one it varies continually in clearness and completeness, reminding one of nothing so much as of the illuminated devices made of gas jets, common at fetes, when the wind sweeps across them, momentarily obliterating one part and at the same time intensifying another. There is not this perpetual flow and flicker in what we perceive. The impressions entering consciousness at. any one moment are psychologically independent of each other; they are equally independent of the impressions and images presented the moment before—independent, i.e. as regards their order and character, not, of course, as regards the share of attention they secure. Attention to be concentrated in one direction must be withdrawn from another, and images may absorb it to the exclusion of impressions as readily as a first impression to the exclusion of a second. But, when attention is secured, a faint impression has a fixity and definiteness lacking in the case of even vivid ideas. One ground for this definiteness and independence lies in the localization or projection which accompanies all perception. But why, if so, it might be asked, do_ we not confound percept and image when what we imagine is imagined as definitely localized and projected ? Because we have a contrary percept to give the image the lie; where this fails, as in dreams, or where, as in hallucination, the image obtains in other ways the fixity characteristic of impressions, such confusion does in fact result. But in normal waking life we have the whole presentation-continuum, as it were, occupied and in operation: we are distinctly conscious of being embodied and having our senses about us. But how is this contrariety between impression and image possible ? With eyes wide open, and while clearly aware of the actual field of sight and its filling, one can recall or imagine a wholly different scene: lying warm in bed one can imagine one-self out walking in the cold. It is useless to say the times are different, that what is perceived is present and what is imagedis past or future.l The images, it is true, have certain temporal marks—of which more presently—by which they may be referred to what is past or future; but as imaged they are present, and, as we have just observed, are regarded as actual whenever there are no correcting impressions. We cannot at once see the sky red and blue; how is it we can imagine it the one while perceiving it to be the other? When we attempt to make the field of sight at once red and blue, as in looking through red glass with one eye and through blue glass with the other, either the colours merge and we see a purple sky or we see the sky first of the one colour and then of the other in irregular alternation. That this does not happen between impression and image shows that, whatever their connexion, images as a whole are distinct from the presentation-continuum and cannot with strict propriety be spoken of as revived or reproduced impressions. This difference is manifest in another respect, viz. when we compare the effects of diffusion in the two cases. An increase in the intensity of a sensation of touch entails an increase in the extensity; an increase of muscular innervation entails irradiation to adjacent muscles; but when a particular idea becomes clearer and more distinct, there rises into consciousness an associated idea qualitatively related probably to impressions of quite another class, as when the smell of tar calls up memories of the sea-beach and fishing-boats. Since images are thus distinct from impressions, and yet so far continuous with each other as to form a train in itself unbroken, we should be justified, if it were convenient, in speaking of images as changes in a new continuum; and later on we may see that this is convenient. Impressions then—unlike ideas—have no associates to whose presence their own is accommodated and on whose intensity their own depends. Each bids independently for attention, so that often a state of distraction ensues, such as the train of ideas left to itself never occasions. The better to hear we listen; the better to see we look; to smell better we dilate the nostrils and sniff; and so with all the special senses: each sensory impression sets up nascent movements for its better reception? In like manner there is also a characteristic adjustment for images which can be distinguished from sensory adjustments almost as readily as these are distinguished from each other. We become most aware of this as, mutatis mutandis, we do of them, when we voluntarily concentrate attention upon particular ideas instead of remaining mere passive spectators, as it were, of the general procession. To this ideational adjustment may be referred most of the strain and " head-splitting " connected with recollecting, reflecting and all that people call headwork; and the " absent look " of one intently thinking or absorbed in reverie seems directly due to the absence of sensory adjustment that accompanies the concentration of attention upon ideas. 22. But, distinct as they are, impressions and images are still closely connected. In the first place, there are two or three well-marked intermediate stages, so that, though we connexion cannot directly observe it, we seem justified in assum- of Impress ing a steady transition from the one to the other. As skins and the first of such intermediate stages, it is usual to Images. reckon what are often, and—so far as psychology goes—inaccurately, styled after-images. They would be better de-scribed as after-sensations, inasmuch as they are due either (i) to the persistence of the original peripheral excitation after the stimulus is withdrawn, or (2) to the effects of the exhaustion or the repair that immediately follows this excitation. In the former case they are qualitatively identical with the original sensation and are called " positive," in the latter they are complementary to it and are called "negative " (see VISION). These last, then, of which we have clear instances only in connexion with sight, are obviously in no 1 Moreover, as we shall see, the distinction between present and past or future psychologically presupposes the contrast of impression and image. 2 Organic sensations, though distinguishable from images by their definite though often anatomically inaccurate localization, furnish no clear evidence of such adaptations. But in another respect they are still more clearly marked off from images, viz. by the pleasure or pain they directly occasion. sort re -presentations of the original impression, but a sequent presentation of diametrically opposite quality; while positive after-sensations are, psychologically regarded, nothing but the original sensations in a state of evanescence. It is this continuance and gradual waning after the physical stimulus has completely ceased that give after-sensations their chief title to a place in the transition from impression to image. There is, however, another point: after-sensations are less affected by movement than impressions are. If we turn away our eyes we cease to see the flame at which we have been looking, but the after-image remains still projected before us and continues localized in the dark field of sight, even if we close our eyes altogether. This fact that movements do not suppress them, and the fact that yet we are distinctly aware of our sense-organs being concerned in their presentation, serve to mark off after-sensations as intermediate between primary and secondary presentations. The after-sensation is in reality more elementary than either the preceding percept or its image. In both these, in the case of sight, objects appear in space of three dimensions, i.e. with all the marks of solidity and perspective; l but the so-called after-image lacks all these. Still further removed from normal sensations (i.e. sensations determined by the stimuli appropriate to the sense-organ) are the "recurrent sensations" often unnoticed but probably experienced more or less frequently by everybody—cases, that is, in which sights or sounds, usually such as at the time were engrossing and impressive, suddenly reappear several hours or even days after the physical stimuli, as well as their effects on the terminal sense-organ, seem entirely to have ceased. Thus workers with the microscope often see objects which they have examined during the day stand out-clearly before them in the dark; it was indeed precisely such an experience that led the anatomist Henle first to call attention to these facts. But he and others have wrongly referred them to what he called a " sense-memory "; all that we know is against the supposition that the eye or the ear has any power to retain and reproduce percepts. " Recurrent sensations " have all the marks of percepts which after-sensations lack; they only differ from what are more strictly called " hallucinations " in being independent of all subjective suggestion determined by emotion or mental derangement. In what Fechner has called the " memory after-image " or the primary memory-image, as it is better termed, we have the image proper in its earliest form. As an instance of what is meant may be cited the familiar experience that a knock at the door, the hour struck on the clock, the face of a friend whom we have passed unnoticed, may sometimes be recognized a few minutes later by means of the persisting image, although—apparently--the actual impression was entirely disregarded. But in vision the primary memory-image can always be obtained, and is obtained to most advantage, by looking intently at some object for an instant and then closing the eyes or turning them away. The image of the object will appear for a moment very vividly and distinctly, and can be so recovered several times in succession by an effort of attention. Such reinstatement is materially helped by rapidly opening and closing the eyes, or by suddenly moving them in any way. In this respect a primary memory-image resembles an after-sensation, which can be repeatedly revived in this manner when it would otherwise have disappeared. This seems to show that the primary memory-image in such cases ' The following scant quotation from Fechner, one of the best observers in this department, must suffice in illustration. " Lying awake in the early morning after daybreak, with my eyes motionless though open, there usually appears, when I chance to close them for a moment, the black after-image of the white bed immediately before me and the white after-image of the black stove-pipe some distance away against the opposite wall. . . Both [after images] appear as if they were in juxtaposition in the same plane; and, though—when my eyes are open—I seem to see the white bed in its entire length, the after-image--when my eyes are shut—presents instead only a narrow black stripe owing to the fact that the bed is seen considerably foreshortened. But the memory-image on the other hand completely reproduces the pictorial illusion as it appears when the eyes are opep" (Flemente der Psvchoihysik, ii. 473).owes its vivacity in part to a positive after-sensation; at any rate it proves that it is in some way still sense-sustained. But in other respects the two are very different: the after-sensation is necessarily presented if the intensity of the original excitation suffices for its production, and cannot be presented otherwise, however much we attend. Moreover, the after-sensation is only for a moment positive, and then passes into the negative or complementary phase, when, so far from even contributing towards the continuance of the original percept, it directly hinders it. Primary memory-images on the other hand, and indeed all images, depend mainly upon the attention given to the impression; provided that was sufficient, the faintest impression may be long retained, and without it very intense ones will soon leave no trace. The primary memory-image retains so much of its original definiteness and intensity as to make it possible with great accuracy to compare two physical phenomena, one of which is in this way " remembered " while the other is really present. For the most part this is indeed a more accurate procedure than that of dealing with both together, but it is only possible for a very short time. From Weber's experiments with weights and lines2 it would appear that even after ro seconds a considerable waning has taken place, and after too seconds all that is distinctive of the primary image has probably ceased. On the whole, then, it appears that the ordinary memory-image is a joint effect; it is not the mere residuum of changes in the presentation-continuum, but an effect of these only when there has been some concentration of attention upon them. It has the form of a percept, but is not constituted of revived impressions, for the essential marks of impressions are absent; there is no localization in, or projection into, external space, neither is there the motor adaptation, nor the tone of feeling, incident to the reception of impressions. Ideas do not reproduce the intensity of these original constituents, but only their quality and complication. What we call the vividness of an idea is of the nature of intensity, but it is an intensity very partially and indirectly determined by that of the original impression; it depends much more upon the state of what we shall call the memory-continuum and the attention the idea receives. The range of vividness in ideas is probably comparatively small; what are called variations in vividness are often really variations in distinctness and completeness.3 Where we have great intensity, as in hallucinations, primary presentations may be reasonably supposed to enter into the complex. It is manifest that the memory-continuum has been in some-way formed out of or differentiated from the presentation-continuum by the movements of attention, but the precise connexion of the two continua is still very difficult to determine. We see perhaps the first distinct step of this evolution in the primary memory-image: here there has been no cessation in presentation, and yet the characteristic marks of the impression are gone, so much so, indeed, that superposition without " fusion " with an exactly similar impression is possible. We have now to inquire into the genesis and development of ideation. Genesis and Development of Ideation. 23. We find ourselves sometimes engrossed in present perceptions, as when tracing, for example, the meanderings of an ant; at other times we may be equally absorbed in reminiscences; or, again, in pure reverie and " castle-building." Here are three well-marked forms of conscious life: the first being concerned with what is, the second with what has been, and the third with the merely possible. Again, the first involves definite spatial and temporal order, though the temporal order, as just said, is in the main restricted to the " sensible present "; the second involves only definite time-order; and the last neither in a definite way. Thus, analytically regarded, perception, memory, imagination, show a steady advance. In infancy the first 2 Die Lehre vom Tastsinne, &c., pp. 86 seq. a As we have seen that there is a steady transition from percept to image, so, if space allowed, the study of hallucinations might make clear an opposite and abnormal process—the passage, that is to say, of images into percepts, for such, to all intents and purposes, are hallucinations of perception, psychologically regarded. predominates, while senility lapses back to the second; in the third, where similarities suggest themselves and the contrast of actual and possible is explicit, we have at length the groundwork of logical comparison. Nevertheless, since imagination plays a conspicuous part in child life before much personal reminiscence appears, it would seem probable that ideas do not first arise as definite memory-images or reminiscences. On the other hand, in the so-called homing instincts of the lower animals we have evidence of isolated " memories " of a simpler form than ours. The subject is as difficult as it is interesting and important, and we can hardly hope at present for a final solution. One chief obstacle, as is so often the case in psychology, lies in the unsettled connotation of such leading terms as memory, association and idea. Even what is most fundamental of all, that " plasticity " which we have analysed into retentiveness, differentiation and integration, is sometimes described as if it already involved memory-ideas and their association. Ideas, that is to say, are identified with mere " residua " of former " impressions," and yet at the same time are spoken of as " copies " of these: which is much like saying the evening twilight is a replica of the noonday glare as well as its parting gleam. Again, the continuous differentiation and redintegration of the presentational continuum which mark the progress of perceptual experience are resolved into an original multiplicity of presentational atoms which are associated by " adhesion " of the contiguous. Yet before the differentiation there was no plurality, and after the integration there is only a complex unity, comparable perhaps with another organic whole, but certainly not with a mosaic stuck together with cement. This mistaken identification by the Associationist psychology of later processes with simpler and earlier ones, by which they are only partially explained, has not only obscured the science with inappropriate concepts but has prevented the question on which we are entering—that concerning the genesis and development of ideas—from being ever effectually raised. The discussion of this question will incidentally yield the best refutation of those views. Experience, we say, is the acquisition of practical acquaintance and efficiency as the result of repeated opportunity and effort. This means that strangeness on the cognitive side gives place to familiarity, and that on the active side clumsiness is superseded by skill. But though analytically distinct, the two sides are, as we have already insisted, actually inseparable: to the uninteresting we are indifferent, and what does not call for active response is ignored. If the original presentations whether sensory or motor, be A, B, C, we find then that they gradually acquire a new character, become, let us say, Ay, B7, C7, 7 representing the eventual familiarity or facility, as the case may be. We find, again, a certain sameness in this character, however various the presentations to which it pertains, a sameness which points to the presence of subjectiye constituents, and to these we may assign the " feelings " that enter into accommodation and adjustment. This factor is important as evidence of a subjective co-operation which may enable us to dispense with the mutual " adhesions " and " attractions" among presentations, on which the Associationists rely. But it is obvious that there must be an objective factor as well; and it is this objective factor in the process giving rise to y that now primarily concerns us. We have described that process as assimilation or immediate recognition: the older psychology described it as association of the completely similar, or as automatic association. That the two views have some-thing in common is shown by the juxtaposition of " automatic " and " immediate," " similarity " and " assimilation." To pre-pare the way for further discussion, let us first ascertain these points of agreement. " When I look at the full moon," said Bain, " I am instantly impressed with the state arising from all my former impressions of her disc added together." This we may symbolize in the usual fashion as A+ an + ¢3 + a2+ al. Now, it will be granted (i) that the present occurrence (full moon) has been preceded by a series of like occurrences, enumer- able as 1, 2, 3, • • n; (2) that the present experience (A7) is what it is in consequence of the preceding experiences of these occurrences; and (3) that it " arises instantly " as the joint result of such preceding experiences. But it is denied (1) that this present experience is the mere sum, or even the mere " fusion," of the experiences preceding it; (2) that they were qualitatively identical; (3) that they persist severally unaltered, in such wise that experience " drags at each remove a lengthening chain" of them. In the case of dexterities, where y answers to facility, it is obvious that there is no such series of identicals (al, a2, • an) at all. From the first rude beginning—say the school-boy's pothooks—up to the finished performance of the adept there is continuous approximation: awkward and bungling attempts, passing gradually into the bold strokes of mastery. Nor is the case essentially different in cognition where y answers to familiarity; if we attend, as it is plain we ought, not to the physical fact cognized, but to the individual's perception of it. This, too, is an acquisition, has entailed activity, and is marked by gradual approximation towards clearness and distinctness. The successive experiences of n identical occurrences does not then result in an accumulation of n identical residua. The ineptness of the atomistic psychology with its "physical " and " chemical " analysis is nowhere more apparent than here. Considering the intimate relation of life and mind, and the strong physiological bias shown by the Associationists from Hartley onwards, it is surely extraordinary how completely they have failed to appreciate the light-bearing significance of such concepts as function and development. Facility and faculty (or function) are much the same, both etymologically and actually. As the perfected structure is not so many rudimentary structures " added together," but something that supersedes them completely, must we not say the same of the perfected function? The less fit is not embodied in the fittest that finally survives. Development implies change of form in a continuous whole: every growth into means an equal growth out of: thus one cannot find the caterpillar in the butterfly. Between organic development and mental development there is then more than an analogy. But though assimilation cannot be analysed into a series of identical ideas (a,, as, • • a„), either "added together" or " instantaneously fused," yet it does result in an a which may provisionally be called an idea. Such idea is, however, neither a memory-idea in the proper sense nor an idea within the meaning of the term implied in imagination or ideation. For it is devoid of the temporal signs' indicated by the subscript numerals in al, a2, ., and it does not yet admit of reproduction as part of an ideational continuum, one, that is, divested of the characteristics belonging to the actual and sensibly present. It is, so to say, embryonic, something additional to the mere sensation assimilated, and yet something less than a " free or independent idea." It is, as it has been happily called,' a tied (gebundene) or implicit idea. We have clear evidence of the sense-bound stage of this immature " idea " in the so-called " memory after-image " (cf. § 22). There is, however, nothing in this of memory, save as the term is loosely used for mere retentiveness; and after percept would therefore be a less objectionable name for it. This after-percept is entirely sense-sustained and admits of no ideal recall, though—in minds sufficiently advanced—it may persist for a few moments, and so form the basis of such comparison with a second sensation, as we find in the experiments of Weber, Fechner and others.' At a still lower level, or in actual perception, we cannot assume even this amount of partial independence, though continuity clearly points to something beyond the bare sensation, which is a pure abstraction, as we may presently see. It is saying too little to maintain, as some do, that this " some-thing " is subconscious, on the ground that it is not discoverable by direct analysis. Yet it is saying too much, regardless of this defect, to describe a percept as a presentative-representative 1 On this term cf. below, §§ 24, 28. 'Cf. Drobisch, Empirische Psychologie (1842), § 31; Hoffding, " Ueber Wiederkennen, Association and psychische Activitat," in Vierteljahrsschr. f. wissenschaftl. Philosophie, Bd. xiii. and xiv. To Hoffding we are also indebted for the term Bekanntheitsqualitat, which has suggested the y character used above. Cf. also Ward, " Assimilation and Association," Mind (1894-1895). 3 Recent experiments, however, seem to prove that the after-percept is not the sole factor, and often is not a factor at all in such successive comparison (so-called) ; but that what is now termed " the absolute impression " may supplement it or even replace it altogether. As to what is meant by absolute impression, cf. § 14, c. complex, if representation is to imply the presence of a free or independent idea. To call this " something " a tied or nascent idea on the ground of its possible later development into an independent representation seems, then, nearest the truth. The same meaning is sometimes expressed in a wholly different and designedly paradoxical way, by saying that all cognition (perception) is recognition. This statement has been met by elaborate expositions of the difference between knowing and knowing again, the irrelevance of which any lexicon would show; and, further, by the demand: How on such a view is a first cognition possible, or how is an indefinite regress of assimilation to be avoided? We may confidently reply that it cannot be avoided: an absolute beginning of experience, whether phylogenetically or ontogenetically, is beyond us. Assimilation means further assimilation; in this sense all cognition is further cognition, and a bare sensation is, as said, an abstraction representing a limit to which we can never regress. We find evidence, again, of ideas in the making in what Lewes called preperception. Of this instances in plenty are furnished by everyday illusions, as when a scarecrow'is hailed by the traveller who mistakes it for a husbandman, or when what is taken for an orange proves to be but an imitation in wax. In reality all complex percepts involve preperception; and, so far, it must be allowed that such percepts are directly analysable into presentative-representative complexes. Nevertheless, the representative element is not yet, and may never become, an idea proper. The sight of ice yields a forefeet of its coldness, the smell of baked meats a foretaste of their savour. Such pre-percepts differ from free ideas just as after-percepts do: they are still sense-bound and sense-sustained. Nor can this complication be with any propriety identified either with the association pertaining to memory or with that specially pertaining to ideation; though, no doubt, the two processes—complication and association—are genetically continuous, as are their respective constituents, nascent and free ideas? The whole course of perceptual integration being determined and sustained by subjective interest, involves from the outset, as we have seen, concurrent conative impulses; and thus the same assimilation that results in familiarity and preperception on the subjective side results in facility and purpose on the conative. Knowing immediately what to do is here the best evidence of knowing what there is to do with; the moth that flies into the candle has assuredly no preperception of it, and does not act with purpose. Bearing this in mind, we may now see one way, and probably the earliest, in which tied ideas become free. The contrast between the actual and the possible constitutes, as we have seen, the main difference beween experience at the perceptual and experience at the ideational stage. A subject confined to the former level knows not yet this difference. Such knowledge is attained, not through any quasi-mechanical inter-action of presentations, but usually through bitter experience. The chapter of accidents is the Bible of fools, it has been said; but we are all novices at first, and get wisdom chiefly by the method of trial and failure. Things are not always different in what to us are their essential properties, but they so differ from time to time. Resemblances are frequent enough to give us familiarity and confidence; yet uniformity is flecked by diversity, and thwarted intentions disclose possibilities for which we were not prepared. What was taken for sugar turns out to be salt; what was seized as booty proves to be bait. We catch many Tatars, and so learn wariness in a rough school. In such wise preperceptions displaced by the actual fact yield the " what " severed from the " that," the " ideal " freed at length from the exclusive hold of the real. In a new situation after such adventures the attitude assumed—if, for brevity, we describe it in terms of our own still more advanced experience—is of this sort: " It may be a weasel, if so, I back; it may be a rabbit, if it is, I spring." Instead of unquestioned preperception that " makes 1 Hence the earlier process has been named " impressional association " (Stout, Analytic Psychology, 1896, ii. pp. 27-29), and again " animal association " (Thorndike, Animal Intelligence, an Experimental Study of the Associative Processes in Animals, 1898, pp. 71, 87, and passim). But it seems preferable to confine the term " association " to the later process, in which alone the component presentations have that amount of distinctness and individuality which the term properly connotes.the mouth water," we have the alternative possibilities present, as " free ideas," and action is in suspense, the alternative courses, that is to say, again present only in idea. It is easy to see how in such situations one free idea, a " what " sundered from its " that," will tend to loosen the sensory ties of alternative, still implicit ideas. On the cognitive side, from immediate assimilation an advance is made towards mediate cognition, towards comparison; on the active side there is advance from impulsive action towards deliberate action? We conclude, then, that implicit ideas—the products of assimilation, and integrated as such in complex percepts and the motor co-ordinations to which they lead—are more likely to emerge as free ideas the more this perceptual complexity increases. Perception in the lower animals, who give no signs of either memory or ideation, has apparently no such complexity. A fish, for example, can feel, smell, taste, see, and even hear, but we cannot assume solely on that account that it has any percepts to which its five senses contribute, as they do to our percept, say, of an orange or a peppermint. Taking voluntary movements as the index of psychical life, it would seem that the fish's movements are instigated and guided by its senses, not collectively but separately. Thus a dog-fish, according to Steiner, seeks its food exclusively by scent; so that when its olfactory bulbs are severed, or the fore-brain, in which they end, is destroyed, it ceases to feed spontaneously. The carp, on the other hand, appears to search for its food wholly under the guidance of sight, and continues to do so just as well when the fore-brain is removed, the mid-brain, whence the optic nerves spring, seeming to be the chief seat of what intelligence it has .3 Again, Bateson observes: " There can be no doubt that soles also perceive objects approaching them, for they bury themselves if a stroke at them is made with a landing-net; yet they have no recognition of a worm hanging by a thread immediately over their heads, and will not take it even if it touch them, but continue to feel for it aimlessly on the bottom of the tank, being aware of its presence by the sense of smell."' To this inability to combine simple percepts into one complex percept of a single object or situation we may reasonably attribute the fish's lack of true ideas, and consequent lack of sagacity. The sagacity even of the higher animals does not amount to " general intelligence," such as enables a child " to put two and two together," as we say, whatever " two and two " may stand for. So far as life consists of a series of definite situations and definite acts, so far the things done or dealt with together, the contents of the several foci or concentrations of attention, form so many integrated and comparatively isolated wholes. Round the more complicated of these, and closely connected with them, free ideas arise as sporadic groups, making possible those "lucid intervals," those fitful gleams of intelligence in the very heat of action, which occasionally interrupt the prevailing irrationality of the brutes. And as we cannot credit even the higher animals with general trains of ideas, just as little can we credit them with a continuous memory: indeed, it is questionable how far memory of the past, as past, belongs to them at all. For they live entirely in an up-stream, expectant attitude, and it is in this aspect that " free ideas " arise when they arise at all. We cannot imagine a dog regretting, like one of Punch's heroes, that he " did not have another slice of that mutton." 5 The free idea (a) then at its first emergence has neither an assignable position in a continuous memory-record, as al or a2, nor has it a definite relation as a " generic idea " to possible specializations such as a' or a". These further developments bring us to the general consideration of mental association. 2 Some light is perhaps here thrown on the reciprocal relation of " association by contrast " and " association by similarity " as severally the differentiation of partial similars and the integration of partial dissimilars. 3.J. Steiner, Die Functionen des Centralnervensytems u.s.w., 2te Abth. Die Fische (1888), pp. 50, 126, 19 seq., 1o1. W. Bateson, " The Sense-Organs and Perceptions of Fishes," Journ. Marine Biol. Assoc. (189o), p. 239. Cf. Stout, Manual of Psychology (1899), vol. ii. ch. i.; also F. H. Bradley, " Memory and Inference," Mind (1899), pp. 145 sqq.; and especially Thorndike, Animal Intelligence, cited above.
End of Article: OBJECTS

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