134 Studies in Animal Behavior 



ing regarded as anything more than a very tenta- 

 tive working hypothesis. 



With our present knowledge of the psycho-physi- 

 ology of pleasure and pain, the attempt to explain 

 how these states or their physiological concomitants, 

 whatever they may be, can act as agents of rein- 

 forcement and inhibition seems rather a fruitless 

 one. The process which we meet at the beginning 

 of intelligence in simple associative memory may 

 be formulated as follows: 



stimulus — reaction — ^pleasure — reinforcement 



^ A ^ 



physiological state x 



stimulus — reaction — pain — inhibition 



' : 1 ■ ■■ 



physiological state y 



Spencer, Bain and others have endeavored to show 

 how the organic accompaniments of pleasure and 

 pain modify the creatures' subsequent responses. 

 But as the problem was Interpreted by these writers 

 our Ignorance concerning the physiological states x 

 and y brings us to a standstill. 



In his valuable work on Mind in Evolution 

 Hobhouse has presented a new point of view in 

 considering this problem, which has the advantage 

 of not Involving any general theory of the physi- 

 ology of pleasure and pain. It is essentially a the- 

 ory of how behavior comes to be adaptively modi- 

 fied through the formation of associations. It makes 



