SPATIAL QUALITY OF TOUCH. 



935 



half "double." But with certain observers 1 and in certain series 2 of observa- 

 tions they have not occurred. With increasing separation of the points of 

 contact the proportion of right answers to total answers increases ; at a certain 

 separation the answers are all right. Throughout the observations single 

 contacts are intermingled with double contacts. 



When " touch spots " are sought out for excitation with the compass points, 

 liminal distances are found much smaller than the average liminal distance of 

 the region. 



Some " aesthesiometers " allow of the reading of the pressure applied to 

 each of the points. 3 



In vividness and delicacy of local sign, touch resembles the muscular and 

 visual senses. It, however, falls far short of the last, being at best more than 

 three thousand times less delicate when skin distances are compared with retinal. 



Table, of Liminal Distances for the "Sense Spots," in Millimetres.* 



As said above, the "touch spots" tend to be arranged in tiny 

 systems radiating from centres. The compass points are perceived to 

 lie apart with especial distinctness, when applied to "touch spots" 

 of two such separate systems. The above list shows that the liminal 

 distance is least for " touch spots," and greater for " warmth spots " 

 than for " cold . spots." The direction of the axis joining any two 

 stimulated " touch spots " is judged with greater nicety than is that 

 of the line joining temperature spots of similar distance apart. 6 



The same has been noted with " average liminal distance." 6 

 Weber's method, as applied by himself, 7 C. Vierordt, 8 and others, 9 is, 

 however, of special value for giving an idea of the "average liminal 

 distance " for a cutaneous region. It is this rather than the special 

 details of liminal distance in relation to the distribution of "touch 

 spots " that yields data valuable for dealing with the majority of 

 space perceptions elaborated from tactual sensation. In estimating the 



1 Kottenkamp and Ulrich, Volkmann. 2 Hartmann. 



3 Griesbach, Arch. f. d. ges. PhysioL, Bonn, 1897, Bd. Ixviii. S. 67. 



4 Goldscheider, Arch. f. PhysioL, Leipzig, 1885. 



5 Goldscheider, ibid. 



6 Czermak, Untersuch. z. Naturl. d. Mensch. u. d. Thiere, Bd. i. S. 188. 



7 Wagner's " Handworterbuch," loc. cit. 8 Tubingen Diss., 1871-1875. 



9 Kottenkamp and Ulrich, Ztschr. f. Biol., 1870, Bd. vi. S. 37 ; Paulus, ibid., Bd. 

 vii. S. 237; Knoller, ibid. ; Riecker, ibid., 1873, Bd. ix. S. 95; 1874, Bd. x. S. 177; 

 Hartmann, ibid., 1875, Bd. xi. S. 79. 



