E. GARCIA-AUSTT, J. BOGACZ AND A. VANZULLI 609 



more concentrated a few minutes after the beginning of the experiment 

 when they were teehng more comfortable. 



Form afid frajiiciicy. During habituation the evoked potential had a 

 tendency to become more complex and to present a greater number of 

 waves (Fig. 2 A). The waves multiplied progressively. This change was 

 more noticeable in the fnst negative wave where a notch appeared which 

 as it became deeper was transformed into a surface negative-positive- 

 ncgativc wave. In some cases all the waves were multiplied, the evoked 



A B 



^ "^^'^'^-A /V^/>aA/V. i-V'^s/^'WA/*^ 



t ' ■ t ' ' t 



Fig. 2 

 Changes of the visual evoked response by effect of liabituatioii. Continuous flicker 

 frequency, Stroboscope at 3 m. from the retina. Forty superimposed sweeps. 

 Technique of Calvet and co-workers. Arrows indicate the stimulus. Lead 02-right 

 mastoid. A, B, and C, experiments performed on different subjects. (1) at the 

 beginning of the experiment; (2) when habituation was achieved. A, the initial 

 component before habituation is constituted by three w-aves and after habituation 

 the amplitude decreases and the waves become more numerous. B, with eyes 

 open, after habituation the amplitude is reduced and a fast after-discharge of 

 22/scc. develops. C. with eyes closed, after habituation the amplitude docs not 

 change and a slow after-discliargc of 14/sec. sets in. Calibration, 200 msec. 



potential being consticuted by a succession of 6 to 8 cycles of low 

 amplitude. Occasionally the progressive reduction of the amplitude 

 finally caused the disappearance of some waves, notably of the first 

 negative wave which generally was of lesser magnitude than the following 

 ones (Fig. i). 



Provided the flicker stimulation was a low frequency (0.5-2 sec.) and 

 that it was prolonged for a lengthy period, there constantly appeared in 

 succession to the evoked response a regular rhythm, present throughout 

 the whole extension of the sweep (which lasted up to 2 seconds (Fig. 2, 

 B and C) ) . This rhythm was of variable frequencies of two ranges :( i ) alpha 



