234 JOHN D. DODSON 



the experimenter know which is the most favorable to habit 

 formation. 



During the years, 1907 and 1908 Dr. Yerkes and the writer 

 attempted to work out, in the Harvard Psychological Labora- 

 tory, the problem as to the relation of strength of stimulus to 

 rapidity of habit formation (12). The subject used for this 

 experiment was the dancing mouse; the habit for the dancer to 

 acquire was a simple visual discrimination between two boxes 

 of different light intensity. We used three degrees of difficult- 

 ness of discrimination, easy, medium and difficult; and three 

 strengths of stimuli, weak, medium and strong. The data se- 

 cured led to the following conclusions : 



1. In the case of the particular habit which we have studied, the 

 rapidity of learning increases as the amount of difference in the bright- 

 ness of the electric boxes between which the mouse is required to dis- 

 criminate is increased. The limits within which this statement holds 

 have not been determined. 



2. The relation of the strength of electrical stimulus to rapidity of 

 learning or habit-formation depends upon the difficultness of the habit, 

 or, in the case of our experiments, upon the conditions of visual 

 discrimination. 



3. When the boxes which are to be discriminated between differ very 

 greatly in brightness, and discrimination is easy, the rapidity of learning 

 increases as the strength of electrical stimulus is increased from the 

 threshold of stimulation to the point of harmful intensity. Our results 

 *do not represent, in this instance, the point at which the rapidity of learn- 

 ing begins to decrease, for we did not care to subject our animals to 

 injurious stimulation. We therefore present this conclusion tentatively, 

 subject to correction in the light of future research. Of its correctness 

 we feel confident because of the results which the other sets of experi- 

 ments gave. 



4. When the boxes differ only slightly in brightness and discrimina- 

 tion is extremely difficult the rapidity of learning at first rapidly in- 

 creases as the strength of stimulus is increased from the threshold, but, 

 beyond an intensity of stimulation which is soon reached, it begins to 

 decrease. Both weak stimuli and strong stimuli result in slow habit 

 formation. A stimulus whose strength is nearer to the threshold than 

 the point of harmful stimulation is most favorable to the acquisition of a 

 habit. 



