218 WALTER S. HUNTER 



(II) of six untrained rats was now chosen. To this group was 



added one rat from set I, not included in the above three. These 



seven rats were given ten trials daily. Table I gives the results. 



Not only did these rats not learn to discriminate the tone from 



its absence, but the data indicate that they reacted as poorly 



at the close of the 700 tests as at the beginning. The objection 



may be made that the number of trials was insufficient ! Such 



a criticism I should regard as valid only if the animals were slowly 



improving in accuracy. This was not the case. Particular 



attention should be drawn to the case of Rat No. 5. This rat 



had learned to discriminate " noise from tone " within 400 trials. 



The above table shows that when tested on mere sensitivity to 



the tone, there was no improvement in accuracy even at the end 



of 700 trials. 



TABLE I. 



The learning processes of the rats of set 11. The numbers stand for the trials 

 in each successive fifty that were correct. 



The present work is of interest when compared with that of 

 Johnson on pitch discrimination in dogs. At the present writing 

 his complete results have not appeared; but the preliminary 

 report « shows that the dogs could not discriminate between 

 middle C and the E above. The possibility that the dogs can- 

 not hear these tones is not considered, although the data are in 

 harmony with such a view. 



6 Johnson, H. M., " Some Experiments on Pitch-Discrimination in Dogs." 

 Psych. Bull., 1912, 9, p. 59. 



