T. PINTO HAMUY 



597 



(/)) To enable us to analyse the experimental situation ironi the point 

 of view of the factors responsible for the failure of our rats to acquire 

 an avoidance CR, we kept all other elements of the experiment constant, 

 changing only the CS (Saavedra, Garcia, Oberti and Pinto-Hamuy, 

 1959). For this purpose we used a sound of 2400 c./sec. as CS. A group of 

 fifteen rats with an average of ablated cortex of 62 per cent was trained. 

 The animals managed to learn even though their performance was 

 inferior to that of the normal control group (Fig. 7). They achieved a pcr- 

 tormance averaging 65 per cent of the CR at the thirtieth session of 

 training. 



10 15 



TEN TRIAL UNITS 



Fig. 7 

 Learning curves of an auditory conditioned reflex (ACR) correspond- 

 ing to groups of normal and ncodecorticated rats. 



The performance app>ears high if we compare the level reached by this 

 group with the results obtained when trying conditioning by means of a 

 light signal. 



We wondered whether this could be related to an easier conditioning 

 with auditory signals. To answer the question we compared the learning 

 of CR of normal rats using luminous and auditory stimuli similar to those 

 employed in the decorticated animals (Saavedra, Garcia, Oberti and 

 Pinto-Humay, 1959). There is a difference which appears in favour t^f the 

 auditory group, this difference being, however, substantially less marked 

 than in the decorticated animals (Fig. 8). These results agree with those 

 obtained by Chow ct al. (1957) in cats who established an ACR in 450 

 trials to light but needed only 150 using a tone. Morrell and Jasper (1956) 

 observed a similar order of difficulty for the conditioning of an alpha 



