LIGHT DISCRIMINATION IN THE ENGLISH SPARROW 



99 



nated this same intensity after 135 trials. But when she failed 

 with the difference in intensity .030 c.p. she seemed to have 

 gotten into the habit of immediately going to one side or the 

 other without any effort at discrimination. Consequently when 

 the difference in intensity was later increased it took a long time 

 to break up this habit. Male IV continued to discriminate the 

 lights without hesitation until the difference in intensity was 

 decreased to .025 c.p. Then the curve starts up abruptly. This 



•0« 



Figure 4. Number of trials necessary for Male V (- 



-) and Female VI 



( ) to learn each discrimination. The difference in intensity is shown 



on abscissae. Number of trials is represented on ordinates. Curve for Female 

 VI shows large number of trials necessary when difference in intensity is small. 



shows that as the discrimination became more difficult, the bird 

 required more trials to learn the discrimination. But when the 

 difference in intensity of the illuminated areas was reduced to 

 .009 c.p. Male IV was unable to learn the discrimination even 

 after 390 trials. The difference in intensity was increased to 

 .013 c.p. At this position he finally succeeded in learning the 

 discrimination after 315 trials. But in the ascending series he 

 was not able to learn to discriminate correctly even after 360 

 trials. The difference in intensity was increased to .017 c.p. 



