The Sense of Hearing 81 



is unsafe, since an animal does not necessarily respond to 

 stimuli by a visible change in the position or relations of its 

 body. Death feigning may fairly be considered a response 

 to a stimulus or stimulus complex, yet there may be no sign 

 of movement. The green frog when observed in the labora- 

 tory usually gives no indication whatever, by movements that 

 are readily observable, that it hears sounds which occur 

 about it, but I have been able to show by means of indirect 

 methods of study that it is stimulated by these same sounds. 1 

 Its rate of respiration is changed by the sounds, and although 

 a sound does not bring about a bodily movement, it does very 

 noticeably influence movements in response to other stimuli 

 which occur simultaneously with the sound. I discovered 

 that under certain rather simple experimental conditions the 

 green frog would regularly respond to a touch on the back 

 by drawing its hind leg up toward the body. Under the 

 same conditions the sound of an electric bell caused no visible 

 movement of the leg, but if at the instant the back was touched 

 the bell was rung, the leg movement was much greater than 

 that brought about by the touch alone. This suggests at 

 once the desirability of studying the sense of hearing in the 

 dancer by some indirect method. The animal may be 

 stimulated, and yet it may not give any visible sign of the 

 influence of the auditory stimulus. 



Were not the dancing so extremely variable in rapidity 

 and duration, it might be used as an index of the influence of 

 auditory stimuli. Cyon's statements would indicate that 

 sounds interfere with the dancing, but as I obtained no 

 evidence of this, I worked instead with the following indirect 

 method, which may be called the method of auditory choice. 



The apparatus which was used is described in detail in 



1 "The Sense of Hearing in Frogs." Journal of Comparative Neurology 

 and Psychology, Vol. XV, p. 288, 1905. 

 G 



