VISUAL PATTERN-DISCRIMINATION IN THE 



VERTEBRATES— II 



COMPARATIVE VISUAL ACUITY IN THE DOG, THE 

 MONKEY AND THE CHICK 



H. M. JOHNSON 



Nela Research Laboratory, 

 National Lamp Works of General Electric Company 



In an earlier paper 1 the present writer discussed the question 

 of discrimination of visual detail in animals, in its bearing on 

 other problems of vision, and on that of vision as a factor in 

 evolutionary theories. In attacking experimentally the four 

 elementary problems suggested in that paper, the first question 

 to be settled is, how large must the pattern be, the degree of 

 contrast being given, in order for the animal to distinguish the 

 pattern from a plain field, having the same area, form, range of 

 wave-lengths and luminous intensity as the field on which the 

 pattern appears. This information is necessary before one may 

 safely assume that two patterns to be discriminated one from the 

 other, are both distinguishable as such. The pattern to be 

 distinguished from the plain field in the present work is simply a 

 series of horizontal black and white striae of equal width with res- 

 pect to each other, but whose absolute width may be varied by 

 insensible gradations from invisibility to marked coarseness 

 without changing any other stimulus-factor. 



The writer chose as subjects the dog, the monkey and the 

 chick (Gallus domesticus). The choice was dictated partly by 

 an interest in the relation between visual acuity and the structure 

 of these different types of eyes, and partly by a desire to add 

 further data to those already accumulated by other students in 

 other problems of vision in these animals. The present work (on 

 pattern-vision in general) promises to extend over a considerable 

 period of time, and it seems best to publish the results in a series 



1 " Visual Pattern-Discrimination in the Vertebrates." I. Problems and Methods. 

 This Journal, vol. 4, 1914, pp. 319ff. 



340 



