Yerkes, Modifiability of Behavior. 271 



11. The results of this investigation indicate, then, that the ac- 

 quisition of a visual discrimination habit depends upon two inde- 

 pendently variable (within limits) capacities in the dancer: (1) 

 the power to detect differences in illumination or to gain this power 

 (educability of white-light vision), and (2) the power to associate 

 the darker box with the electric shock (associative memory). The 

 former of these capacities seems to be greater in the young than 

 in the old dancer;, the latter seems to be somewhat greater in the 

 old than in the young individual. 



12. Should the statements just made hold true for animals gen- 

 erally, it is evidently important that the senses be trained early in 

 life and that the development of associative memory be furthered 

 later. Investigation of the problems suggested by our results should 

 yield important practical data for the science of education. 



