JOURNAL OF ANI MAL BEHAVIOR 



Vol. 6 MAY-JUNE No. 3 



VISUAL PATTERN-DISCRIMINATION IN THE 

 VERTEBRATES— III 



EFFECTIVE DIFFERENCES IN WIDTH OF VISIBLE 

 STRIAE FOR THE MONKEY AND THE CHICK 



H. M. JOHNSON 



Nela Research Laboratory, National Lamp Works of General Electric Company 



In an experiment reported some time ago 1 I determined the 

 width of the individual members of a regular system of striae 

 necessary to enable three animals to distinguish the field as 

 striate at a given distance and under the experimental condi- 

 tions prescribed. The work reported in this paper was done 

 on the same animals, in an attempt to ascertain what difference 

 in width of the members of two regular systems of striae, both 

 of which the animals can distinguish as such, is necessary to 

 effect discrimination between the two systems. The discrimi- 

 nands are two interchangeable circular fields, 6 cm. in diameter 

 and equal in brightness and color. The distribution of energy 

 through the visible spectrum approximated that of a tungsten 

 lamp operated at a specific consumption of 1.25 watts per candle. 

 In the work on the chickens the mean brightness of the fields 

 was 12.24 candles per square meter; in the work on the monkey, 

 6.67 candles per square meter; and in a supplementary test made 

 on two human subjects, 6.24 candles per square meter. The 

 striae composing the system on the positive field are coarser 

 and fewer in number than those composing the system on the 

 negative field. The animals were fed in the food-compartment 



1 Johnson, H. M. Visual pattern-discrimination in the vertebrates. II. Com- 

 parative visual acuity in the dog, the monkey and the chick. This journal, vol 4, 

 1914, pp. 340-361. 



