TACTUAL JUDGMENTS. 943 



distance apart appear further apart if tested where the " local sign " 

 is strong than where it is weak. The points of a pair of compasses, 

 when moved with a sufficient speed over a length of skin, appear to get 

 wider apart as they pass from skin less endowed with local sign to skin 

 more endowed, e.g. from ear to lip. 1 Moved in the opposite direction, 

 they seem conversely to close together. Moreover, if moved with 

 uniform speed, they appear to travel faster as they pass over the more 

 perceptive region, e.g. towards lip. 2 



When two skin-points {a and b) are simultaneously touched with the 

 compass-tips, the distance between them appears greater than if one 

 compass point travels — not too slowly — from a to b. The quicker the 

 travel the shorter appears the distance ; the slower the travel the longer 

 the distance ; so that it may, if quite slow, appear longer than if a and b 

 be simultaneously touched. 3 It is easier to read letters as they are 

 traced on the skin than letters already fully shaped and pressed upon 

 the skin. It must be remembered here that for the reason given above 

 (p. 936, note 1), the deformation of the skin will be greater in the former 

 case than in the latter. 



If a body, e.g. a ball, be touched with a rod, the eyes being blind- 

 folded, and its periphery followed by touching it with the rod, the 

 dimensions appear smaller the longer the rod used. 4 



Owing to the inequality of the " average liminal distance " when 

 measured along various axes in a single region of skin, it is easy to be 

 deceived about the form of surface in contact with the skin. The cross- 

 section of a circular tube pressed on the skin appears transversely oval ; 

 whereas contact with a true oval, and its longer axis lengthwise, along 

 the limb, appears circular. Again, experiment shows that if a metallic 

 tube, with triangular, circular, or rectangular cross-section, is pressed on 

 the skin, it is not easy, unless the tube be much larger than the " sensory 

 circles " of the skin in question, to distinguish its shape. A circle can 

 be " felt as circular " by the tongue-tip, if the diameter be not less than 

 3"3 mm. ; but to be felt to be circular by the skin of the abdomen it 

 must measure 55 mm. across. 5 



An experiment, which as long ago as the days of Aristotle was of 

 recognised psychological interest, is the following. If one crosses the 

 first and middle fingers, and then places between them a small round 

 body, e.g. a pea, the pea is " felt double," as though it were two peas. 

 The illusion is strengthened by moving the surfaces of contact. The 

 two sides of the lingers in use are in their ordinary position invariably 

 turned away from each other. Experience has taught that they usually 

 touch two different objects, and this association may be, in the un- 

 practised person, sufficient to override the correcting perception fur- 

 nished by the muscular sense. 



If a penholder be held between the lips, it can be felt to be straight. If 

 one of the lips be displaced sidewise, the holder seems broken. This illusion 

 vanishes in front of a mirror. So also with transplanted portions of 

 skin : in the nose made from a flap of frontal skin, touches continue for 

 months to be referred to the forehead. 



Tactual judgments of form. — For judgment of the shape of objects 

 and their dimensions by touch, we possess four methods of acquiring data, — 



1 Weber, loc. cit. - Vierordt, loc. cit. 3 Fcchner, Vierordt, loc. cit. 



4 Tourtual, cited by Vierordt, "Griindriss d. Physiol.," Tiibingen, 1877. 

 6 Vierordt, loc. cit. 



