VISUAL PATTERN-DISCRIMINATION IN THE 

 VERTEBRATES— IV 



EFFECTIVE DIFFERENCES IN DIRECTION OF VISIBLE 

 STRIAE FOR THE MONKEY AND THE CHICK 



H. M. JOHNSON 

 Nela Research Laboratory, National Lamp Works oj General Electric Company 



The purpose of the experiments described below was to ascer- 

 tain how small a difference in direction of two regular systems 

 of visible striae will condition the responses of animals possess- 

 ing eyes of different types. In this work I used the "discrimi- 

 nation method" described by Yerkes and Watson, 1 feeding the 

 animal in a compartment of the training box indicated by the 

 "positive" test-object, and punishing him for attempting to 

 enter the food-compartment indicated by the "negative" test- 

 object. A detailed description of the method of training and 

 of preparing the stimuli has appeared in an earlier report. 2 

 In the present work the discriminands were two circular fields, 

 6 cm. in diameter and 6.24 candles per square meter in bright- 

 ness. The energy-distribution in the visible spectrum approx- 

 imated that of a tungsten lamp operated at a specific consump- 

 tion of 1.25 watts per candle. Both fields were covered with 

 alternate dark and bright striae equal in width and separation. 

 The chicks and the monkey had previously demonstrated their 

 ability to react with perfect accuracy under the experimental 

 conditions to the presence or absence of the striae from the 

 test-field. The striae on the positive field were horizontal; those 

 on the negative field deviated from the horizontal direction by 

 a definite and variable amount. In the beginning of the train- 

 ing the difference was 90°, and was decreased by small grada- 

 tions after the animal had formed the habit of invariably choos- 

 ing the food-box indicated by the positive test-field. 



Yerkes, R. M. and Watson, J. B. Methods of studying vision in animals. 

 Behavior Monographs, vol. 1, no. 2, 1911. 



2 Johnson, H. M. Visual pattern-discrimination in the vertebrates. I and 

 II. This journal, vol. 4, 1914, pp. 319-361. 



189 



