450 STELLA B. VINCENT 



The aktograph records of Szymanski (34) showed that the 

 periods of activity of the fish were regulated by light. They 

 began about one hour before sunrise and ended about one and 

 one-half hour after sunset. 



Birds. — Light discrimination in the English sparrow was the 

 object of Tugman's (37) experiments and the main attempt 

 was to find the threshold of brightness. The Yerkes-Watson 

 brightness apparatus and experiment box was used. The birds 

 were kept in darkness before the beginning of the work. Correct 

 choices for two days (30 trials) were counted as a correct dis- 

 crimination and then the difference between the standard .098 

 and the variable was decreased and the tests were resumed. 

 The discrimination differences attempted ranged from .096 to 

 .009 and the estimated thresholds for four birds were, .015, 

 .035, .03, .022 c-. p. The estimated thresholds for some human 

 subjects were .013, .009, .013 c. p. The author says, " One of 

 the most striking facts is the very large number of trials neces- 

 sary to bring the animal to the threshold. The three animals 

 for which the threshold was determined averaged 2,420 trials 

 each. For the discrimination of the lowest threshold they 

 averaged 480 trials each ; one of them discriminated only after 

 615 trials. 



As will be seen we are at last getting some well controlled 

 work on sensory discrimination in animals. The first of the 

 studies from the Franklin Field Station which Yerkes describes 

 in the same journal (41) is reported by Coburn (4). He gives 

 a preliminary study of the crow's ability to discriminate bright- 

 ness, size and form. In the investigation he used but two 

 birds. The apparatus was a modified form of the discrimination 

 box used by Breed and Cole in their study of the visual re- 

 actions of chicks and the stimulus plates were the Standard 

 plates of the Yerkes-Watson apparatus. Both method and 

 apparatus are carefully described in the report. The crows 

 learned to discriminate between an opal flashed glass and an 

 opal flashed glass backed first by two milk glasses, second, by 

 one milk glass; third, by a sheet of paper. These roughly in- 

 dicate the crows' ability to distinguish differences in illumination. 

 Then they learned to discriminate between a 9 cm. and a 2 cm. 

 circle; between a 5 cm. and a 3 cm. circle and between a 3 cm., 



