No. 635] 



BODILY ROTATION 



529 



disappearance of this one movement accounts for the sud- 

 den falling off of the time-values at the end of the various 

 series. The average initial time of after-nystagmus for 

 all subjects was 5.57 sec. for rotation to the left and 5.74 

 sec. for rotation to the right. Other averages testify to 

 this difference in time for the two directions of rotation. 

 This seems to be a genuine case of individual difference 

 quite comparable to similar differences found in human 

 observers. 8 



The fact of decrease from day to day is incontestable. 

 Each column in Table I shows it. It is just as apparent, 

 if, in each day's series, an average of the first two trials 

 is taken and compared with corresponding values for 

 subsequent days. That is, each day begins at just a little 

 lower nystagmus-time than the preceding day began. 

 Furthermore, the decrease is of a characteristic kind. 

 Table I indicates that at least one half of the total de- 

 crease commonly occurs in the first few days of exper- 

 imentation. The exceptions, subjects "G" and "H," 

 will be considered later. In this respect, a "nystagmus 

 curve'' is quite comparable with the common "learning 

 curve," save for the absence of plateaus. 



Again, the figures make it plain that there is also a gen- 

 eral decrease in the time of after-nystagmus within any 

 single day's turning. Table II indicates that this de- 

 crease was constant for all subjects, save "G" and "H." 

 An analysis of the material upon which the table is based 

 shows that the main decrease within any single day falls 

 early in the series — a result consonant with the early fall 

 in time from day to day, as just mentioned. 



It must be emphasized that any decrease is for one set 

 of conditions only. Only those values are given which 

 resulted when the rat rested quietly on the floor of the 

 rotated platform. Occasionally the rat would stand al- 

 most upright, in which case the nystagmus was almost 



