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EXTENSION ( See also: action of straining or stretching out
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It is usually employed metaphorically (cf. the phrase an "extension of See also: time," a See also: period allowed in excess of what has been agreed upon)
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It is used as a technical See also: term in logic to describe the See also: total number of See also: objects to which a given term may he applied; thus the meaning of the term " See also: King " in " extension " means the
See also: kings of See also: England, See also: Italy, See also: Spain, &c
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(cf
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DENOTATION), while in " intension " it means the attributes which taken together make up the idea of kinghood (see See also: CONNOTATION)
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In psychology -the literal sense of extension is retained, i.e
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" spread-outness." The perception of space by the senses of sight and touch, as opposed to semi spatial perceptions by smell and hearing, is that of " continuous expanse composed of positions separated and connected by distances " (Stout) ; to this the term " extension " is applied
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The perception of See also: separate objects involves position and distance, but these taken together are not extension, which necessarily implies continuity
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To move one's See also: finger along the keys of a piano gives both the position and the distance of the keys; to move it along the See also: frame gives the idea of extension
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By expanding this idea we obtain the conception of all space as an extended whole
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To this perception are necessary both See also: form and material
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It should be observed the actual quality of a stimulus (rough, smooth, dry, &c.) has nothing to do with the spatial perception as such, which is concerned purely with what is known as " See also: local signature." The elementary undifferentiated sensation excited by the stimuli exerted by a continuous whole is known as its " extensive quantity " or " extensity." The term has to do not with the kind of See also: object which excites the sensation, but simply with the vague massiveness of the latter
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As such it is distinguishable in thought from extension, though it is not easy to say whether and if so how far the quantitative aspect of space can exist apart from spatial See also: order
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Extensity as an See also: element in the complex of extension must be carefully distinguished from intensity
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See also: Mere increase of pressure implies increase of intensity of sensation; to increase the extensity the See also: area, so to speak, of the exciting stimulus must be increased
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Thus the extensity (also called " voluminousness," or " massiveness ") of the sensation produced by a See also: roll of See also: thunder is greater than that produced by a See also: whistle or the bark of a See also: dog
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It should be observed that this application of the idea of extensity to sensation in general, rather than to the See also: matter which is the exciting stimulus, is only an See also: analogy, an attempt to explain a See also: common psychic phenomenon by terminology which is intrinsically suitable to the See also: physical
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As a natural consequence the term represents different shades of meaning in different See also: treatises, verging sometimes towards the physical, sometimes towards the psychic, meaning
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In connexion with extension elaborate psycho-physical experiments have been devised,.e.g. with the object of comparing the accuracy of tactual and visual perception and discovering what are the least differences which each can observe
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At a distance two See also: lights appear as one, just as two stars distinguishable through a See also: telescope are one to the naked See also: eye (see VISION) : again if the points of a compass are brought close together and pressed lightly on the skin the sensation, though vague and diffused, is a single one
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See PSYCHOLOGY and See also: works there quoted; also SPACE AND TIME
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