PLEASURE, PAIN AND INTELLIGENCE '61 



much as in the ordinary posture for defense. Crayfish and crabs 

 often assume this attitude while alarmed and retreating from dan- 

 ger, but the crayfish would come toward my hand and moreover 

 would react in this way only when hungry, so that the response 

 was not a fear reaction but one showing rather the absence of 

 fear. One individual would greet me as I entered my room in the 

 morning by raising up its chelipeds and coming toward me, and 

 it would follow me about as I went from one side of its inclosure 

 to the other. When fed, however, it would manifest no further 

 interest in my movements. I had come to mean food and was 

 responded to, I fancy, much as the crayfish would respond to a 

 small object of prey which it could approach without fear. A 

 part of the crayfish's congenital endowments is the instinct to 

 approach small moving objects, as it is to flee from large ones. 

 This instinctive reaction to small objects normally precedes the 

 movements of seizing and devouring, just as the latter are pre- 

 ceded, though more uniformly, by twitchings of the antennules; 

 the two sets of processes are parts of a normally associated chain 

 of events. 



The appearance of a large moving object has been associated 

 with a mode of response (food taking) which is incongruous with 

 the fear response : the latter is therefore inhibited. The reaction 

 proper to the small object normally pursued has become joined 

 to the food taking activities and the large object is followed. 

 The large object may mean food, but there must be supplied an 

 impulse to go toward the object. This probably comes, not from 

 a fiat of the creature's will, but from an already existing instinc- 

 tive proclivity to pursue objects of possible interest or food. 



According to the view here presented, whether a particular 

 response to a stimulus tends to be repeated more readily or dis- 

 continued, depends not upon the peculiar physiological state which 

 may be produced in the brain, but upon the kind of responses 

 which the stimuli brought by the act call forth. If an outreaching 

 reaction becomes coupled with a withdrawing response the result 

 is inhibition. If the reaction, on the other hand, brings stimuli 

 which produce congruent reactions the association formed with 

 these latter reinforces the first reaction. The pleasure-pain 



