Yerkes, Inhibition and Reinforcement. 



127 



Title of investigation. 

 Experimented on. 

 Harvard Psychological Laboratory. 

 Chronoscope control average, 189 6. 



No Light. 



Number of Experiment. 



TABLE IL 



Electric-Visual (Red Light). 

 Green Frog No. 4. 



9.40 A. M.,Feb. 28, 1902. 

 . Electric stimulus, i Cell. 



4 

 5 

 6 



7 

 8 



9 

 10 



Light before Electric Stim. 



No Light. 



12 

 13 

 14 



15 



16 



216 



The inhibitory influence of light in this case depends upon the 

 intensity of the electric stimulus. Even a very strong light will 

 not cause much retardation of reaction to a 3 or 4 cell current. 

 As the strength of the electric stimulus decreases the delay of 

 reaction increases, until finally there is complete inhibition. At 

 this point, an electric .stimulus to which the frog would react 

 almost invariably when there is no disturbing condition, will 

 fail to cause reaction in the presence of a sudden increase in 

 light intensity. 



Merzbacher ('00, p. 253) states that the leg reflex of a 

 frog, so placed that its legs hang free in the air, is greater in 

 response to a given cutaneous stimulus in darkness than in 

 daylight. ^ 



^ "Blendung oder blosse Lichtentziehung erholit die Erregbarkeit fiir me- 

 chanische Reize." (p. 253.) 



