620 BRAIN MFXHANISMS AND LEARNING 



in man. The facilitation of the specific response to an intermittent sound 

 after conditioning by association with a continuous Hght, was observed in 

 the cat by Jouvct (1956) and Jouvet and Hernandez-Peon (1957). The 

 resuks described in different conditions of stimulation (continuous light, 

 intermittent sound) agree with the statement previously made, that the 

 association of a continuous tone and ot an intermittent flight, facilitated 

 the evoked response by light in man, after conditioning. Buser and 

 Rougeul (1956) established that the 'rcponse irradiee' increases in ampli- 

 tude in the course of sensorial conditioning. It has already been stated in 

 this paper that it is probable that this response corresponds to the diffuse 

 respt^nse of the scalp record in man. 



Dishabituation by conditioning was described in the cat by Hernandez- 

 Peon, Jouvet and Scherrer (1957). The auditory response was dishabituated 

 on the acoustic stimulus being given a new significance by association with 

 an electric shock to the forepaw of the animal. Lelord, Fourmant, Calvet 

 and Scherrer (1958) described in man the conditioning of the response 

 evoked by sound (conditioned stimulus) by association with light (un- 

 conditioned stimulus). After various trials on successive days a diffuse 

 response was obtained by a sound which before the conditioning evoked 

 no response. This is a phenomenon of delayed appearance, differing, 

 therefore, from the rapid changes of the visual evoked response already 

 described. 



When the visual stimulus acted as an unconditioned stimulus in the tone- 

 flicker association the changes in the response were greater than when it 

 took the form of a conditioned stimulus in the flicker-tone association. In 

 other words the changes in the vsiual 'unconditioned' response were 

 greater than in the visual 'conditioned' response. This fact agrees with the 

 view sustained by other authors as Buser and Roger (1957), 'que c'est au 

 niveau de la zone corticale inconditionellc que se concentre I'essentiel des 

 cvenements caracteristiques de la liaison conditionclle'. 



Persons subjected to the tone-flicker interaction stated that after various 

 associations they became aware that the tone was always followed by a 

 series of flashes and consequently when they started listening to it they 

 were already prepared to see the light, thus paying more attention to it. 

 On the other hand, the flicker-tone association had the same effects on 

 attention to sound, the effects on attention to light being variable. 



CONCLUDING REMARKS 



The amplitude, form and distribution of the scalp visual evoked re- 

 sponse in man depend on the significance of the photic stimuli. 



