CHAPTER IV 



Sensory Discrimination : Methods* of Investigation 

 § lo. 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 

 absence 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 t hex-QQjsse-SS- Consciousne ss. Further, 

 a point that was mentioned in Chapter I must again be 

 emphasized. No evidence 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 quahty 

 of the sensation resulting from each may be, whether it 



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