March 33, 191 :] 



SCIENCE 



479 



definite physiological condition. The the- 

 ory of Spencer and Bain is open to obvious 

 criticism, for the man who steps on a tack 

 undoubtedly has a "heightened nervous 

 discharge," as much as a man who shouts 

 for joy. And I believe I am safe in saying 

 that no theory of the physiology of pleas- 

 ure and pain is on a sufficiently firm basis 

 to warrant its being regarded as anything 

 more than a very tentative working hy- 

 pothesis. 



With our present knowledge of the 

 psycho-physiology of pleasure and pain, 

 the attempt to explain how these states or 

 their physiological concomitants, whatever 

 they may be, can act as agents of reinforce- 

 ment and inhibition seems rather a fruit- 

 less one. The process which we meet at 

 the beginning of intelligence in simple as- 

 sociative memory may be formulated as 

 follows : 



stimulus — reaction — pleasure — reinforcement 



physiological state x 

 stimulus — reaction — pain — inhibition 

 physiological state y 



Spencer, Bain and others have endeav- 

 ored to show how the organic accompani- 

 ments of pleasure and pains modify the 

 creatures' subsequent responses. But as 

 the problem was interrupted by these 

 writers our ignorance concerning the 

 physiological states x and y brings us to 

 a standstill. 



In his valuable work on ' ' Mind in Evo- 

 lution" Hobhouse has presented a new 

 point of view in considering this problem, 

 which has the advantage of not involving 

 any general theory of the physiology of 

 pleasure and pain. It is essentially a the- 

 ory of how behavior comes to be adaptively 

 modified through the formation of associa- 

 tions. It makes no attempt to explain why 

 pleasure is associated with certain experi- 

 ences and pain with others. Such associa- 

 tion may turn out to be as inexplicable as 



the problem why stimulation of the optic 

 nerve gives rise to a sensation of light 

 instead of some other kind of feeling. 

 What it is feasible to attempt to explain is 

 why certain responses tend to be repeated 

 and others tend to be inhibited. And this 

 can be explained with some plausibility as 

 due to the congruity or incongruity of the 

 reactions which come to be associated. For 

 the sake of illustration let us consider 

 again the chick Avhich pecks at a nasty 

 caterpillar. The irritation set up by the 

 caterpillar in the chick's mouth evokes 

 movements of withdrawal and ejection. 

 The two responses of pecking and ejection 

 become associated, but as the two move- 

 ments are contradictory the result is in- 

 hibition. The pecking reaction no longer 

 occurs in the presence of a second nasty 

 caterpillar, not because of any stamping- 

 out influence of the physiological concomi- 

 tant of pain, but because it becomes joined 

 with an antagonistic reaction. 



In a previous paper by the writer the 

 attempt was made to extend the theory of 

 Hobhouse to account for the reinforcement 

 commonly held to be caused by pleasure. 

 The assumption was made that this process 

 is due to an organic congruity of the reac- 

 tions. If the caterpillar pecked at is a 

 savory one there is set up the reflex of 

 swallowing. Peeking and swallowing form 

 the normal elements of a chain reflex; 

 when one part of the structure concerned 

 is excited it tends to increase the tonus of 

 the associated parts, and thits reinforce the 

 original response. I have found that in 

 the crayfish stimulation of the antennules, 

 which are important organs of smell, sets 

 up chewing movements of the mouth parts 

 and grasping movements of the small 

 chelse. Similarly stimulating the small 

 chela evokes chewing movements of the 

 mouth parts and twitching of the anten- 

 nules, while stimulating the mouth parts 



