78 WALTER S. HUNTER 



are capable of reactions that seem explicable only on the assump- 

 tion of the functional efficiency of a representative factor. If 

 sensations can function in this manner, the law of parsimony 

 forbids the assumption of images. (3) That sensations can 

 function in this manner is indicated by the illustrations from 

 human psychology noted above. It is a different matter, I 

 know, to say that the sensations of animals also may function 

 in this manner. But in order to explain the behavior of the 

 raccoons, it is necessary to assume either the presence of images 

 or the presence of sensations that function in this manner. The 

 law of parsimony favors the latter type of process because sen- 

 sations are genetically earlier than images. 



Inasmuch as the rats and dogs, as well as the raccoons, used 

 sensory processes in the solution of our problem, we are forced 

 to recognize that sensations may be placed in two classes on the 

 basis of function: (i) There are sensations that can initiate 

 a correct reaction from at least three possible responses only 

 when they have not been displaced, during the interval of delay, 

 hy other sensations of the saute modality. Here would fall those 

 sensory experiences of constant orientation possessed by the 

 dogs and rats. (Those cases where these animals lost their 

 orientation and then regained it were few enough to be rated 

 as accidental.) (2) There are sensations that can initiate correct 

 responses, under the above conditions, even though they have 

 been displaced during the interval of delay by others of the 

 same modality. Here would fall the sensory experiences of the 

 raccoons and children. The evidence which indicates that no 

 sensory process need be constantly maintained in order that 

 these subjects may react correctly is unambiguous. It is this 

 type of sensory process that I have denominated sensory thought. 



On the basis of human introspection, there is another grade or 

 kind of learning, V-iz., the stage of the functional efficiency of 

 images or centrally aroused conscious processes. Why there 

 should be both sensory and imaginal thought in human ex- 

 perience is very difficult to say. The most obvious suggestion 

 would be that imaginal thought, since it is genetically later, 

 could accomplish tasks which sensory thought could not. I 

 shall hazard no guesses as to what such tasks might be. At 

 the present stage of psychological theory, there seems to be no 

 question but that the distinction of sensory and imaginal thought 



