E. GARCIA-AUSTT, J. BOGACZ AND A. VANZULLI 607 



and Bishop, 1954), in the waking animal (Buscr and Borcnstcin, 1957) as 

 in man (Ciganck, I9s8a), it may be recorded at a distance. 



The evoked visual response in waknig man studied in this investigation 

 corresponds in its characteristics and distribution to that described by 

 Calvet ct al. (1956) and by Ciganek (1958 a, b). The potential studied by 

 Walter and Grey Walter (1949) is certainly the same one, although 

 described in less detail. On the other hand, other responses recorded in 

 wakmg man such as the 'waking-on-eftect' (Davis, 1939; Davis, Davis 

 Loomis, Harvey and Hobart, 1939) and the 'pointes vertex' (Gastaut, 

 1953), probably respond to dit^^erent mechanisms since they have a different 

 distribution. 



It may be presumed that diis diffuse evoked visual response corresponds 

 in latency, topography and conditions ot recording during wakefulness to 

 the 'reponse irradiee' ot Buser and Borenstein (1957) recorded in cats. 



EFFECT OF CONTINUOUS FLICKER STIMULATION 



On application oi a continuous flicker frequency the evoked responses 

 underwent progressive changes showing modifications in dieir amplitude, 

 form, frequency and topographic distribution. 



Aiiiplitiide. In subjects who had no previous knowledge of the technique 

 and who were unaware of the conditions of the test, the responses to the 

 first flashes were invariably of greater amplitude than to succeeding ones 

 (Figs. I and 2). As time passed the amplitude was progressively reduced. 

 This decrease was apparent after 300-500 flashes and was maintained 

 during the whole experiment, which comprised from 2000 tc^ 4000 

 flashes in 15-20 minutes. 



Frequently, after the initial reduction a ciiscrete increase was found in 

 the amplitude without obtaining, however, the initial values recorded at 

 the beginning of the experiment. On some occasions a repeated waxing 

 and waning was observed, but always maintaining a lesser amplitude than 

 the original one. 



The reduction of the evoked response in man as a consequence of the 

 repetition of the stimulus is similar to the phenomenon of habituation 

 described in the animal by auditory or photic stimulation (Hernandez- 

 Peon, Jouvet and Scherrer, 1957; Jouvct and Hernandez-Peon, 1957; 

 Hernandez Peon, 1958; Hernandez-Peon, Guzman-Flores, Alcaraz and 

 Fernandez-Guardiola, 1958; Palestini, Davidovich and Hernandez-Peon, 

 1959)- 



Hc^wever, the time course of habituation was considerably faster in 



