REACTIONS OF CHICKS TO OPTICAL STIMULI 291 



no. 73 was unfitted for further work by a misuse of the electric 

 shock. When no. 87 had completed 160 trials in the training, 

 the work was discontinued on account of the poor physical 

 condition of the animal. Starting with preference trials of 

 9 reactions to the circle and n to the square, its total number 

 of reactions to the circle during the training was 101 ; to the 

 square, 59. The final two series registered 9-1 and 8-2 in favor 

 of the circle. There were thus indications that the training 

 had been somewhat effective. 



The results from no. 76, on the other hand, were more 

 convincing. Reacting indifferently in the preference tests to 

 the circle and the square of equal area and brightness, it was 

 able to select the circle 38 times out of the last 40 trials in a 

 training series of 120 trials. When the positions of the source 

 lights were shifted from 90 to fixed positions at 80 and 100 cm. 

 respectively, so that the forms were illuminated unequally, no. 

 76 selected the circle 18 times out of 20 trials. Training was 

 then resumed for two series with the forms of equal brightness, 

 after which the sliding screen was mounted from left to right 

 as follows: 5 cm. circle, 4.43 cm. square, and a circle equal 

 to that circumscribed about the 4 . 43 cm. square. Ten trials 

 with this combination netted 8 selections of the circles and 2 

 of the square. When, however, the next change in the forms 

 was made, there appeared to be no sign of discrimination. The 

 corresponding inscribed circle was substituted for the circum- 

 scribed, accompanying as in the previous test the square and 

 circle equal to each other in area, and the first ten reactions 

 recorded were 5 for the circles and 5 for the square. An attempt 

 was now made to train the chick to select these circles in prefer- 

 ence to the square. After this training had been prolonged for 

 70 trials, the chick was selecting the circles as against the square 

 9-1. At this point the frame was set with the circumscribed 

 and the inscribed circles in combination with the square, where- 

 upon the chick made the record 10-0. For the series follow- 

 ing this one, conditions remained the same except that the lamps 

 were exchanged in the illumination boxes and a different tin 

 plate was used to produce the square form. The series resulted 

 9-1. When this series was repeated with a different order of 

 shifts of the frame, the animal made the record 10-0. For 

 data see table 2. 



