220 WALTER S. HUNTER 



the same intensity as a tone produced by a solid rubber ball 

 of 102 gm. striking the fork after a free fall of 25 cm. 



The conditions of testing here were the same as described 

 above. Five trials daily were given, save at certain periods 

 with two rats, with punishment and reward. Between 575 and 

 800 trials were given. There was no more evidence of discrim- 

 ination at the last than at the first. This problem of intensity 

 discrimination was begun simultaneously with the work on noise 

 and tone before I suspicioned that the rats were insensitive 

 (or very slightly so) to the tone in question. 



(3) Miss Alda Barber of this laboratory is studying local- 

 ization of sounds in rats. The standard stimulus, tapping upon 

 wood, is well localized. The following controls have been used 

 with significant results: (a) Tapping with the rubber end of 

 a lead pencil on the resonance box of c' is localized with normal 

 accuracy. This gives a noise predominately of a 512 v. s. pitch. 



(b) A tuning fork c' sounded steadily is completely ignored. 



(c) The same pitch blown upon an organ pipe as an interrupted 

 (tooting) tone is also ignored. It is not known yet whether or 

 not special training will overcome these last two failures. 



(4) Watson » obtained reactions from white rats with the 

 Galton whistle. I have never secured an unambiguous response 

 to tone, although violent starts are often made to the slightest 

 noises. A few times I have thought that reactions occurred. 

 These may well have been to the noise accompanying the whistle 

 tone. Tests have been made with organ pipes and Edelmann- 

 Galton whistles. At least 30 rats have been tested in this labo- 

 ratory both when they were awake and when they were asleep, 

 when they were nervous and responded to slight noises readily 

 and when they were not nervous. A few tests were made upon 

 some twenty rats at the University of Chicago in the summer 

 of 1913. The Edelmann whistle was used throughout its range, 

 but no reactions were observed. Professor R. E. Carter of the 

 University of Kansas witnessed these latter tests and agreed 

 in the findings. Possibly it is true that rats are sensitive to 

 each others squeaks, but who is to say whether these are more 

 tone than noise? 



This type of test is to be carried further. At present this 



•Watson, Jno. B. " Kinaesthetic and Organic Sensations." Psych. Rev. Mon., 

 1907, 8, pp. 53-54. 



