PERCEPTION. 133 



and for sight y of a second.* The observations of Von Wit- 

 tichf, Vintscligau, and Honig-Schnied:|: show that the reaction- 

 time for taste varies between 0'1598^' to 0*2 3 51'' according 

 to the kind of taste ; being least for salt, more for sugar, and 

 most for quinine. A constant electrical current applied to 

 the tongue gives a reaction-time for the resulting gustatory 

 impression of 0'16 V. I am not aware that any experiments 

 have been made with regard to smell. Exner has more 

 minutely determined on himself the reaction- time for touch, 

 sound, and sii>-ht, with the results which are embodied in the 

 following table. The signal was in all cases given by the 

 right hand depressing an electrical key : — 



Direct electrical stimulation of retina . . , . 0*1139'' 



Electrical shock on left hand . . . . . . 0"1276 



Sudden sound 0-1360 



Electric shock on forehead. . .. .. .. 0"1370 



Electric shock on right hand . . . . . . 0'1390 



Visual impression from electric spark . . . . 01 506 



Electric shock on toe of left foot . . . . . . 0'1749§ 



It is thus noticeable that although the sensation of light pro- 

 duced by vision of an electric spark is much greater than 

 that produced by electrical stimulation of the optic nerve, 

 the interval between the stimulation and the perception is 

 much longer in the former case. Seeing that the optic nerve 

 is so short, this difference cannot be attributed tc the time 

 lost in transmission along the nerve, and must therefore be 

 supposed due to the time required for the nerve-endings in 

 the retina to complete all the changes (whatever they may 

 be) in which their response to luminous stimulation consists. 

 Thus in the case of hearing, as the above table sliows, some- 

 what less time is consumed in the whole act of perception 

 than is consumed in the case of sight by the peripheral 

 changes taking place in the retina. 



According to HeLmholtz and Baxt, the more complex an 

 object of visual perception is, the greater must be the dura- 

 tion of its image upon the retina, in order that the perception 

 may be made ; while, within certain limits, the intensity of 

 the image does not affect the time required to make the per- 



* Arch.f. Anat. und PhijsioL, 1^68, p. 657. 



t qt. Ret. Med. (3), xxxi, p. 113. 



X Arch.f. Anat. und PhifftioL, x, p. 1. 



§ Pfiiiger'sArchiv., Bd.'VII, p. 620. 



