THEORY OF "LOCALISING" POWER OF "TOUCH." 939 



In the limbs and mobile parts, when a spot of less discriminative sensitivity is 

 touched, instinct moves the member, so that it brings to the object the part 

 where its own sensitivity is delicate, e.g. the finger-tips. It is apparent to most 

 of us that if, with closed eyes, we attend to the consciousness of the resting 

 arm, the hand, and especially the fingers, are the parts we are most aware 

 of, best outlined, so to say, in consciousness. There arise lines of habitual 

 association between all points of the member and its sensitive tip. James 

 writes : " I think anyone must be aware when he touches a point of his 

 hand or wrist that it is the relation to the finger-tips of which he is usually 

 most conscious." 



" Muscular " sensations may be regarded as varying in intensity according 

 to extensity of movement. A more intense sensation accompanies a larger 

 movement; a more prolonged sensation a longer lasting movement. Touch 

 sensations may be regarded as varying in quality with the place of the skin 

 whence they arise. Touch sensations are yoked with "muscular" in four 

 main modes. (1) The same tactual point is moved successively over various 

 points of an object, i.e. the same touch in regard to quality is yoked with a 

 series of "muscular" sensations differing in intensity; "active touch." (2) An 

 object is allowed to move over a series of tactual points, the tactual surface 

 being held stationary, i.e. one muscular sensation is combined with a series of 

 tactual; "passive touch." (3) One tactual surface is moved over another, 

 i.e. one set of " muscular " sensations is yoked with a double simultaneous 

 series of tactual ; " double touch." (4) The movements of the body, apart 

 from contact with objects, are combined with corresponding series of tactual 

 sensations due to stretching and folding of the skin. Disparate sensations, 

 if connected frequently, become "associated," so that genesis of one in- 

 volves reproduction of the other. In thinking of our arm's movements 

 we always in some degree recall its field of touch. "Muscular" sense is 

 more delicate for shoulder than for hand, yet in recalling a movement of 

 the arm we habitually recall the hand more than the shoulder. Con- 

 versely, perception of a tactual point is fraught with "muscle" sensations 

 linking to it other tactual points whose perceptions frequently precede or 

 succeed or accompany it. These sensual links lend themselves well to 

 measurement, because differing in many instances in mere intensity rather 

 than in quality. The measure of their differences yields by associative ex- 

 perience a basis of estimation of the spatial distances of the tactual points. 

 Tactual space includes the idea of the skin as a continuous surface, although 

 its organs are punctifonn. This results from infinitely graded muscle sensa- 

 tions accompanying infinitely graded rectilinear movements possible in various 

 directions in a plane. 



It is noteworthy how little vision seems to contribute to tactual localisa- 

 tion ; some of the most delicately localising touch surfaces never come within 

 the visual field at all. Tactual localisation differs from auditory and gustatory 

 in that, whereas a single drop of fluid on the tongue may give a mixed sensa- 

 tion, and two sounds may be perceived to come from the same place, two 

 compound touches of different quality, e.g. a blunt and a sharp, applied 

 simultaneously in the same sensory circle, do not combine to any simultaneous 

 sensation, but alternate, as in the struggle of different colours presented to 

 identical spots of the two retinae. 



Weber l described the whole surface of the skin as resoluble by analysis 

 into " sensory circles." If for any part of the skin we measure exactly 

 the distance between compass points the sensations aroused by which 

 appear single, and make this measure in many directions about a single 

 point, we obtain for this part of skin a figure of rounded form within 

 which simultaneous touches appear single. Such an area is a Weber's 



1 E. H. Weber, loc. cit. ; also "Tastsinn u. Gemeingefiihl," Leipzig, 1852, S. 106. 



