Yerkes and Dodson, Habit Formation. 



477 



Fig. 4. Curves of learning. Ordinates represent series of ten tests each, and abscissae represent the 

 average number of errors for four mice in each series. W, designates the error curve for the individuals 

 which were trained under the condition of weak electrical stimulation; M, designates the corresponding 

 curve for the medium strength of stimulation; and S, that for the strong stimulus. 



