252 'Journal of Comparative Neurology and Psychology. 



of habit formation? As an answer to this question, I offer a sum- 

 mary statement of the results of a special investigation of the rela- 

 tion of strength of stimulus to rapidity of learning in which I was 

 ably assisted by Mr. John D, Dodson. This study, unlike that 

 of sensitiveness, was a thoroughgoing quantitative investigation of 

 the significance of the factor under consideration, and we present 

 our results with confidence that their accuracy, despite many tech- 

 nical difficulties, renders the generalizations which they indicate 

 of imj)ortance not only in connection with our present experi- 

 ments, but for all work on animal behavior. 



IV. STRENGTH OF ELECTRIC STIMULUS, IN ITS RELATION TO 

 RAPIDITY OF HABIT-FORMATION. 



Precisely how does increasing or decreasing the strength of the 

 electric stimulus, which the dancer is learning to avoid by associat- 

 ing it with the darker of two boxes, influence the process of learning ? 

 The answer which results obtained with forty dancers enable us to 

 give to this question is exceedingly important in its several as- 

 pects.'' 



fl) We have demonstrated that the influence of the stimulus 

 varies with the difiicultness of the visual discrimination which is de- 

 manded of the mouse, and that condition of disci-imination must be 

 taken into consideration from the first in foniiiilatiug our answer 

 to the above question. 



(2) That when visual discrimination is easy, rapidity of habit-for- 

 mation increases as strength of stimulus is increased from the 

 threshold to the point of injurious stimulation. In our experiments, 

 the strongest stimulus employed was decidedly disagreeable to the 

 experimenters and caused violent reactions in the mouse. Whether 

 beyond this intensity of stimulation the rate of learning increases, 

 we cannot say from the results of experimentation, but we may 

 say with assurance that it cannot possibl}'' increase very much, 

 inasmuch as the stimulus would soon become positively harinfnl. 



'Yerkes, R. M., and Dodson, J. D. The Relation of Strength of Stimulus 

 to Rapidity of Habit-fonuation. Join: Camp. IVciir. and Psi/.. vol. IS, pp. 459- 

 482, 1908. 



