484 



BRAIN MECHANISMS AND LEARNING 



a 



b 



I 



n 



ni 



lY 



Y 



Fig. 4 

 Pairs of test patterns used. In describing a discrimination 

 taught to an animal the positive pattern is hstcd first. For 

 example, in discrimination I-ab, the positive, rewarded 

 pattern is a circular flat patch of white against a black back- 

 ground while the negative pattern is a similar square patch. 



