462 Benj. C. Griienberg 



should expect on the anthropomorphic view of the animal "seek- 

 ing to keep the same vision in sight. " But the turning of the head 

 is opposite to the direction of the spin that the observer uncon- 

 sciously imparts to the dish in moving his arm outstretched, which 

 is thus in the radius of a horizontal rotation. 



That the perception of spin or rotation is located in the organs 

 of the inner ear seems likely from the fact that the response is 

 eliminated when the semicircular canals are destroyed or removed, 

 or when the acoustic nerve is cut. That the sensation concerned 

 involves a factor of rotation or turning is indicated by the fact 

 that rectilinear acceleration does not yield the same constant 

 response. 



It may, therefore, be concluded that the compensatory move- 

 ments of the frog's head set up by rotation arise in response to two 

 distinct sets of stimuli, visual and dynamic; that the response to 

 the visual stimulus is relatively feebler and slower than that to the 

 dynamic stimulus; that the organ for the perception of the dynamic 

 factor is probably located in the internal ear; and that the dynamic 

 perception involves a rotation or turning element in the stimulus, 

 as distinguished from an acceleration or movement in a single 

 direction. 



6 SUMMARY 



1 There is apparent contradiction between the various re- 

 sponses of the frog to rotation on the turntable and any theory of 

 mechanical stimulation of peripheral organ as the origin of the 

 responses. 



2 There is considerable contradiction among various experi- 

 ments that have been made in connection with the relation of the 

 semicircular canals and compensatory movements. 



3 A reexamination of the compensatory movements and of 

 the conditions under which they arise shows the presence of a 

 mechanical factor, the "spin," the significance of which in this 

 connection seems not to have been considered before. 



4 From an examination of the results obtained by earlier 

 observers, a repetition of some of their experiments, and new 

 experiments made in the course of the study, the following con- 

 clusions are drawn: 



