CHAPTER IV 

 SENSORY DISCRIMINATION: METHODS OF INVESTIGATION 



13. Preliminary Considerations 



ONE of the most important points in which the human 

 mind differs from the mind of the lowest animal forms con- 

 sists, we have seen, in the enormously greater number of 

 different sensations which enter into human experience, as 

 compared with the small number of sensory discriminations 

 possible to the simpler animals. Much of the experimental 

 work that has been done on animals has been directed 

 toward discovering what discriminations they make among 

 the stimuli acting upon them, and to the results of this work 

 we shall give our attention in the next chapters. But first 

 we ought to get a clearer idea of just what kind of evidence 

 is needed to indicate the existence of a variety of sensations 

 in an animal's mind. 



At the outset, we must remind ourselves that, in the ab- 

 sence of any satisfactory proof that the lower animal forms 

 have minds at all, and the equal absence of any proof that they 

 have not, all our conclusions about the number and kind of 

 their possible sensations must remain subject to the proviso 

 that they possess consciousness. Further, a point that was 

 mentioned on page 24 must again be emphasized. No evi- 

 dence of discrimination between two stimuli on an animal's 

 part can do more than show us that for the animal they are 

 different; just what the quality of the sensation resulting 

 from each may be, whether it is identical with any sensation 



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