DELAYED REACTION 73 



By applying the term "ideas" to these cues, I mean that they 

 are similar to the memory idea of human experience so far as 

 function and mechanism are concerned. They are the residual 

 effects of sensory stimuli which are retained and which may 

 be subsequently reexcited. The revival, moreover, is selective 

 and adaptive to the solution of a definite problem, and when 

 aroused, they function successfully as a necessary substitute 

 for a definite component of the objective stimulus aspect of 

 the problem. The question as to the content nature of these 

 cues, i.e., their sensory or imaginal character, is reserved for 

 the succeeding section. 



2. The Place of Ideas in the Grades of Animal Learning 



A survey of animal reactions from those of the protozoa to 

 those of the higher vertebrates leads one to the conclusion that 

 the simplest behavior, from a genetic point of view, is the ad- 

 iustment of a certain movement to a certain object or situa- 

 tion. This adjustment may be either native or acquired. In 

 the former case, it is instinct ; in the latter, the result of indi- 

 vidual learning. (As such, it does not seem to be present in 

 the protozoa.) The remarks in what is to follow are directed 

 solely to the latter case. In the literature this is referred to 

 as the stage of learning by experience on a sensori-motor level. 

 Over against this genetically simple learning, may be placed a 

 more complex form of behavior which in\-olves a representative 

 function. This ideational or representative process arises out 

 of a geneticall}^ prior sensori-motor level of behavior. The 

 field of its functioning is limited, moreover, to the representa- 

 tion either of some aspect of the object (or sensory) side or of 

 some part of the movement and its consequences. In other 

 words, the representative process must stand for either the 

 sensory or the motor aspect presented in the genetically lower 

 level of behavior. According to the law of parsimony, the only 

 conclusive evidence in favor of the existence of such a repre- 

 sentative element is the case where successful adaptations occur 

 when that part of the sensori-motor process assumed to be 

 represented is known to be absent at the moment of response. 

 If the object or movement to be represented is present, why 

 assumxc a representative or ideational process? The adjustment 

 can be explained in terms of sensory stimulus and response. 



