50 MILDRED A. HOGE AND ki Til .). STOCKING 



the experiment. Except for the nervousness referred to above, 

 none of the animals experienced any ill effect from the work, 

 and no differences in the general health and activity of the 

 three groups were observed. 



The failure of the rewarded rats to learn the problem in the, 

 time allowed is of particular interest, since their preliminary 

 work (preference tests) was along the same line as the work 

 of the problem; whereas, in the case of the rats which were 

 punished, a new element, the electric shock, was introduced. 



The difference in the rate of visual discrimination between 

 albinos and rats with pigmented eyes deserves notice. In each 

 group the white rat made the discrimination before the rat 

 with pigmented eyes. This is apparently not in harmony with 

 the results obtained by Karl Waugh, 6 w T ho states that " the 

 discrimination of the albino mouse is not so good as that of 

 the mouse with pigmented eyes." In neither the work of Dr. 

 Waugh nor in the present work were a sufficient number of 

 animals used to settle the question of the relative discrimina- 

 tive ability of the two varieties. 



It seems evident from this experiment that a combination of 

 punishment and reward-motives is more effective in bringing 

 about visual discrimination in the rat than is either punishment 

 or reward used alone. It seems evident, also, that punishment 

 is more effective than reward, at least in so far as the rate of 

 learning is concerned. 



6 Karl Waugh. The role of vision in the mental life of the mouse. Jour. 

 Com p. Neurol, and Psychol., 1910, vol. 20, pp. 549-600. 



