VISUAL PATTERN-DISCRIMINATION IN THE 



VERTEBRATES— I 



PROBLEMS AND METHODS 



H. M. JOHNSON 



From the Nela Research Laboratory, 

 National Lamp Works of General Electric Company 



GENERAL BEARING OF THE PRESENT INVESTIGATION 



The present work grew out of an interest in the question of 

 the comparative ability of different vertebrates to discriminate 

 detail in visual objects. The theory of sexual selection, which 

 is of considerable historical importance at least, assumes that 

 certain animals discriminate intricate markings of plumage or of 

 hair. The theory of natural selection also assumes that some 

 animals can discriminate details in visual objects, although its 

 demands are less severe and less definite than are those of the 

 theory of sexual selection. The question is of interest to some 

 students of behavior apart from its direct bearing on either 

 theory. 



As regards the factor of vision in the theory of sexual selection, 

 it is evident that two distinct questions are involved. One is, 

 Do animals react to differences in marking ? Are individuals 

 possessing a coat of a given pattern aided or hindered thereby in 

 securing a mate ? This question may be attacked without study- 

 ing the vision of the animals. If one were to observe the courting 

 behavior of a large number of individuals and note the number 

 and conditions of copulation or mating of all the members of the 

 group, correlation of these data with the kind of markings 

 possessed by the individuals would throw light on the question. 

 The other question is, Can the animal respond to differences in 

 visual detail, and if so, how great must these differences be ? 



CHOICE OF RESPONSES FOR STUDY 



The observable facts in a study of an animal's special senses 

 are the responses which the animal makes to stimuli affecting 



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