E. GARCIA-AUSTT, J. BOGACZ AND A. VANZULLI 



619 



discontinuous flicker without tone association. But the subject rapidly 

 became rehabituated it the trials were repeated (extinction). This rehabitua- 

 tion was much more rapid than that caused by persistence ot the initial 

 association (tone-flicker). 



FLASMCS (CrS) TRIALS (DFS) TRIALS (DrS + TONC) 



Fig. 10 



Clitiin^es of the visual evoked response by effect of coiitiiiuoiis ami discontinuous flicl<er stinnilation 

 and throngli tone-flicker association. Ordinatcs, percentage of initial peak to peak amplitude 

 of the evoked response. Abscissas, time, represented by the number of flashes during the 

 continuous flicker stimulation (CFS) at a frequency of 2/sec. and by trials carried out every 

 20 seconds with discontinuous flicker stimulation (DFS) at the same frequency for 20 

 seconds. Stroboscope at a distance of 1.5 m. from the retina. Eyes open. Black and white 

 dots, simultaneous records from the occipital and the central regions respectively. Dur- 

 ing the CFS the response decreases in amplitude chiefly in C4. During the DFS an increase 

 of the amplitude in C4 is observed. In O2 the response does not show significant changes. 

 When a tone is emitted at the end of the periods of darkness (tone-flicker association, 

 DFS + tone), the amplitude of the central responses increases even more. The occipital 

 response undergoes no changes. 



In most, the variations in the responses were different in the central, 

 temporal and occipital regions, being more marked and persistent in the 

 first two. 



The changes in the evoked visual response by the interaction of tone 

 and flicker constitute another example of the electrocortical conditioning 



