THE BEHAVIOR OF THE CROW 191 



the test, would become so restless that in many cases it would 

 begin to throw itself against the woven wire side of the box. 

 By the time its turn came, the desire to escape from the box 

 had entirely overcome the desire for food, and, as a result, it 

 would rush through the test and recommence its struggle to 

 free itself. If, by chance, it made a correct choice, the food 

 would not be noticed. 



The results of each series of tests were kept on record sheets 

 similar to those used by H. C. Bingham • in his study of the 

 perception of size and form in the chick. In addition to a 

 record of the correct and incorrect choices, the time required 

 for the choice and a sketch of the path of the crow were also 

 recorded. 



In the study of brightness perception, the apparatus remained 

 as in the preliminary series except that the stimulus areas of 

 the stimulus-chambers differed in intensity. This difference 

 was obtained by the use of more or less opaque substances, 

 namely, black cardboard, milk glasses, and paper. These were 

 placed over the opal flashed glass of one of the stimulus areas. 

 The slides, which held the plates of opal flashed glass before 

 the stimulus areas, were large enough to admit also the card- 

 board, milk glasses, or sheets of paper. 



Black cardboard was first used. Since it allowed no light to 

 pass, the illumination of the stimulus area before which it was 

 placed was practically zero. The crows, in the trial series, had 

 become partially accustomed to stimulus areas of an intensity 

 produced by light passing through but one thickness of opal 

 flashed glass. Consequently in the brightness experiments, they 

 avoided the darkened chamber. The chambers were darkened 

 in no regular order, but in ten or twenty tests, one chamber 

 would be darkened as many times as the other. 



After fifteen tests with each crow, the cardboard was ex- 

 changed for two milk glasses, then later for one milk glass and 

 finally for one sheet of paper. The difference in the intensity 

 of the two areas in this last case was comparatively slight. With 

 care it could be distinguished by the human eye. 



Table 1 shows the results of these tests. 



• Bingham, H. C. Size and Form Perception in Galhis domesticus. Jour, of 

 Animal Behavior, 1913, vol. 3, no. 2, pp. 65-113. 



