VISUAL DISCRIMINATION OF SIZE AND FORM 

 IN THE ALBINO RAT 



K. S. LASHLEY 

 From the Psychological Laboratory of The Johns Hopkins University 



One figure 



In the exact experimental work of comparative psychology 

 evidence of visual image formation has been obtained for all 

 of the higher groups of vertebrates, but few investigators have 

 attempted to determine the accuracy of the animal's percep- 

 tion of outlines. 



L. J. Cole, (1907) obtained evidence of the perception of size 

 in the frog. Casteel, (191 1) working with the turtle, found that 

 it could distinguish slight differences in the breadth and direc- 

 tion of lines, but did not discriminate between similar patterns. 

 For the birds, Porter, (1904-06) has demonstrated the ability 

 of the English sparrow and cow-bird to discriminate printed 

 patterns and, less accurately, tridimensional objects. In his 

 work with the dancing mouse Yerkes, (1907) obtained no reac- 

 tions to form and concluded that the perception of form has 

 little importance in the activities of the mouse. Waugh, (1910) 

 in similar experiments, obtained only slight evidence of form 

 discrimination and was led to the same conclusion. By L. W. 

 Cole, (1907) the raccoon has been trained to distinguish perfectly 

 between objects of different size and form, square and circular 

 cards, etc. Kinnaman, (1902) found that his mcnkeys could 

 compare the size of the food boxes used and form some absolute 

 standard of comparison. They also distinguished between ves- 

 sels of different form but did not recognize differences in printed 

 patterns. 



The present investigation has attempted to determine the 

 visual acuity of the rat, making use of the " form and size 

 methods" (Washburn, 1908). Like the mouse, the albino rat is 

 without an area centralis (Chievitz, 1891 and Slonaker, 1897), 

 and the retina contains only rod-like sensory elements. From 

 the likeness of structure and habitat, a similarity of visual 

 function is to be expected. 



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