THE AUDITORY SENSITIVITY OF THE WHITE RAT 217 



Result — the reactions remained at a normal accuracy. In other 

 words, the presence of the tone was not essential for correct 

 reactions. (2) The noise was withheld and tone given at one 

 trial and the absence of noise at the next. Result- — the rats 

 failed. The rat always turned to the left for the noise. It turned 

 to the right for each of the following : tone, the absence of tone, 

 and the absence of noise. 



Two interpretations > were now possible: (1) The rats may be 

 unable to hear c' 512 either because of a shortening of the scale 

 similar to the probable shortening of the rat color spectrum, or 

 because of an inability to hear tone at all, i. e., complete tonal 

 deafness, or because of a tonal island. In either of the three 

 cases, we have a sensory defect. Furthermore, it would be a 

 defect common to all of the rats tested. (2) The ignoring of 

 c' 512 may be due to a factor of attention as Dr. Weidensall 

 has pointed out in her report at the American Psychological 

 Association. 1912.* Our dilemma here is the same as the one 

 which confronted the Watsons, » e.g., when their rodents were 

 shown to be ignoring red in the red-green discrimination. The 

 solution in either case must come from evidence drawn from tests 

 made on mere sensitivity, i.e., the discrimination of a stimulus 

 from its absence. In view of this the following tests were made. 



Three of the rats of set one, were each given 10 trials daily, 

 in an attempt to set up an association between the tone and 

 turning to the right and between absence of tone and turning to 

 the left. 410, 520 and 350 trials were given, but the association 

 Was never set up. These three rats had formed the original 

 discrimination of noise vs. tone in 310, 370 and 520 trials respec- 

 tively. In all save the third rat, therefore, the original discrimi- 

 nation was set up in fewer trials than given in this control. I 

 have not regarded this as entirely conclusive, however, because 

 as a result of previous training the rats were all ignoring the tone. 

 This habit (if habit it were) may have persisted. A new set 



» There is a third possibility, viz. : the rats may have been unable to discriminate 

 the tone from its auditory background. It was impossible to carry out the tests in a 

 sound-proof room, so this possibilitiy has not been rigorously excluded. However, 

 the rats were accustomed to what auditory stimuli did occur, and as far as the ex- 

 perimenter was concerned, the tone dominated over all other sounds save in excep- 

 tional cases that rarely occurred. 



* Weidensall, Jean. A Critique of the Discrimination Test. Psych. Bull., 1912, 

 9, pp. 57-58. 



« Watson, J. B. and Watson, Mary I. A Study of the Responses of Rodents to 

 Monochromatic Light. Jour. Animal Behavior, 1913, 3, pp. 1-14. 



