LITERARY NOTICES. 



Simultaneous Tactile Impressions.' 



Professor Krohn has carried on, in connection with Mr. Bolton, 

 of Clark University, a series of interesting experiments "to determine 

 the relative sensitiveness of different portions of the skin, to find the 

 nature and direction of the errors in localization, to study the influ- 

 ence of attention upon the localization and interpretation of the 

 simultaneous touch stimulations, also the investigation of the problem 

 of attention, with special reference to the question of how many sen- 

 sations of touch the the mind can attend to, or grasp, at one time, and 

 to examine the effect of practice." The stimuli were applied by 

 pointed corks attached to tambours which connected by separate pipes 

 with a common air chamber. Pressure brought to bear on the con- 

 fined air in the chamber caused the cork points to strike the skin of 

 various parts of the body practically synchronously. It was shown 

 (i)that the skin over the joints is more sensitive than elsewhere, and 

 permitted greater accuracy ot localization ; (2) that touches on the 

 back are more distinctly felt and more clearly remembered, and thus 

 better localized than on the front of the body ; (3) localizations are 

 more correct near the median line ; (4) that the localization is more 

 accurate on the right side ; (5) piliferous parts are more sensitive ; 

 (6) exposed surfaces are better localized. 



It is suggested that the superior sensitiveness of the dorsal surface 

 sustains some relation to a previous quadrupedal attitude. 



' ' The localizing power is delicate in proportion as the skin covers 

 a more moveable part of the body and is also more acute when the 

 pressure stimulation is only strong enough to cause an appreciable 

 sensation than when it is more powerfully impressed." 



After images are pronounced in some cases, but still more inter- 

 esting is the fusion of two or more stimulations into a single sensation 

 and the localization of this sensation at a point removed from either of 

 those at which the stimulations were received ; thus, in one case, there 

 were three touches, one on each nipple and one over the breast-bone 



' William O. Krohn. An Experimental Study of Simultaneous Stimu- 

 lations of the Sense of Touch. Journ. Nerv. and Mental Disease. March, 1893. 



