LOCALIZATION OF SOUND IN THE WHITE RAT 303 



was given. This had been eliminated as far as possible by 

 fastening the stimulus board to the table and not to the main 

 apparatus box. In control II, a layer of cotton batting 1 in. 

 thick was placed under the apparatus box in order further to 

 eliminate vibrations. The resulting responses were at normal 

 accuracy. A final argument to prove conclusively the non- 

 essential character of the vibratory cue was found in control 

 III where the substitute stimulus, a resonator box, was held 

 in the hand outside the screen. Extraneous vibrations were 

 here eliminated, yet the reactions were made at a normal accuracy. 



The elimination of olfactory, kinaesthetic-tactual and visual 

 cues indicated that the response of the rat was determined by 

 auditory factors. The problem now concerned the auditory 

 factors determining the accuracy of localization. Other aud- 

 itory timbers and pitches, the interrupted character of the 

 stimulus and intensity were investigated. 



d. Auditory controls — For use in later comparison, a pre- 

 liminary control (III) was put in. A stimulus noise was found 

 which was of a predominant pitch 256 d. v., and of an interrupted 

 character. This was the tapping upon a resonator box with 

 the pencil rubber as described above in the section on apparatus. 

 The pitch was determined by Helmholtz resonators. The 

 intensity has also been described previously, and was approx- 

 imately equal to that of the chisel which gave the normal stim- 

 ulus. Thus in this control, we have a predominant pitch 256 

 d. v., the interrupted character of the sound and the standard 

 intensity. The reactions, which showed no break from the 

 normal accuracy, were as follows: 



TABLE III 



The three series of averages shown, were secured on three 

 successive days. 



Whether or not the pitch element per se of the standard 

 stimulus was the fundamental factor in determining the locali- 



