134 ILLINOIS ACADEMY OF SCIENCE 



CHART III 

 The line AB represents the stimulus limen just above which incre- 

 ments of rotational stimulation will just excite ocular movements. If the 

 increments of stimulus, c,c,c, etc., are given at intervals, the threshhold 

 value rises as at A'B'. 



order to represent faithfully the course of nystagmus the 

 unbroken threshhold line will have to take the direction 

 of the dotted line. In other words, the threshhold value 

 is constantly rising. 



It is apparent, therefore, that nystagmus is profoundly 

 influenced by practice even though the excitation of the 

 end-organs in the canals is constantly ''subliminal" so 

 far as regards the production of any observable eye- 

 movement. Moreover, the continued absence during our 

 experiments of all the other effects of rotation indicates 

 that after-iiA^staginus is but a single constituent of a large 

 group of rotational residues. That is to say, the organic 

 and the mental effects of rotation usually appear and 

 disappear together. These facts, together with the com- 

 parison of respective threshhold values under repetition 

 point directly to the conclusion that the ocular move- 

 ments following rotation cannot be considered as the 

 simple and invariable reflex effects of ampullar excita- 

 tion. 



