322 



WALTER S. HUNTER 



rats 45 and 46 were disturbed by control 7 where the normal 

 whistle stimulus was simply sounded at a less intensity than 

 usual. When the standard whistle is decreased in intensity 

 the change is much the same as occurs when the whistle is taken 

 to a distance, i. e., the noise accompanying the whistle is de- 

 creased in intensity if not eliminated and similar changes most 

 probably occur among the overtones. Therefore, even from an 

 a priori standpoint, one need not be surprised that the reactions 

 with control 7 were of less than normal accuracy. The import- 

 ant fact is that they were significantly better than the reactions 

 with control 6. Inasmuch as the stimuli in the two controls, 

 were, for the experimenter, extremely similar in respect to in- 

 tensity magnitude, it seems most probable that the rats were 

 governed in their responses by the noise usually accompanying 

 the whistle tone. There is no evidence that the animals heard 

 the stimulus in control 6. 



Controls 8 and 9. — In a previous experiment rats that had 

 been trained to respond to the noise of handclapping were unable 

 to make discriminative responses when tones were substituted 

 for the standard stimulus, although the substitution of other 

 noises was attended by positive results. The same facts appear 

 here with the piston whistle tests. It will be seen from the 



numerical summary here given that all of the rats failed un- 

 qualifiedly to respond in control 8 to the tuning fork 1280 d.v. 

 Rat 46's percentage for control 8 would be only 54, if 20 trials 

 were ruled out when the animal was responding to extra-auditory 

 cues. (See above page 290, and appendix table 6.) 



There was no tuning fork available whose vibration rate was 

 at or above 2000 d.v. It was therefore impossible to use a fork 

 of a pitch equal to the standard whistle. However, the next 

 best thing was done. The whistle pitch was lowered in control 

 9 to the pitch of the fork used in control 8 (1280 d.v.). The 

 data given above indicate that the rats reacted as well to this 



