132 ILLINOIS ACADEMY OF SCIENCE 



menter.^ Finally the rapid decrease in all the values for 

 subject A during three or four minutes rotation indicates 

 that lost practice effects are soon recovered. In the case 

 of subjects B and D, it will be seen from Table II thai 

 neither of them had gone beyond seven revolutions per 

 trial. Over four weeks later, ten revolutions per trial 

 produced but a third of the original values. These facts 

 clearly point to the conclusion that the modification of the 

 time of after-nystagmus, the number of the ocular move- 

 ments and the time of apparent movement in the visual 

 field, is more or less permanent. More specifically, the 

 facts prove conclusively that the modifications are not 

 due to fatigue. 



TABLE IV 



Giving the time of after-nystagmus in seconds, the number of ocular 

 movements, and the time of the apparent movement of objects in the 

 visual field after rotation-trials of ten revolutions (except for sub- 

 ject E). Compare this table with the results shown in Table I. 



(5 rev.) 

 F 40 1 0.0 0.0 0.0 0.0 0.0 0.0 



In general, then, our experiments have demonstrated 

 that repeated excitation of the semicircular canals which 

 is not of sufficient intensity to produce any observable 

 ocluar effects leads within a comparatively short time to 

 the ability to stand as many as ten turns within twenty 

 seconds without the appearance of after-nystagmus, or of 

 any of the other organic and mental products of rotation. 

 Now if a single excitation of the canals, such as we have 

 used, is called a "subliminal stimulus," so far as regards 

 the production of ocular effects, then these ocular effects 



"See Griffith, C. R. op., cit., pp. 46, 124. 



