The Visual Perception of Distance. 



BY JOHN K. ROUSE. 



If we omit Descartes, the scientific study of the perception of 

 distance began with Bishop Berkele}'. Assuming that a difference 

 in the distance of a point can make no difference in the nature of 

 the retinal image, since "distance being a line directed endwise to 

 the eye projects only one point upon the fund of the eye — which 

 point remains invariably the same, whether the distance be greater 

 or smaller," he concluded that distance could not be a visual sen- 

 sation, but must be an intellectual "suggestion," due to some non- 

 visual experience, and this experience he considered tactile. 



According to his view, visual perception of distance is the ac- 

 quired interpretation of light and color differences in terms of 

 distance already gained by skin and muscle. To say that an object 

 is a certain distance, is to assert that so much sensation of skin and 

 muscle must be had before the object can be touched. 



But the notion that distance is not a visual, but a tactile form of 

 consciousness, suggested b}- visual signs, though endorsed b}' many 

 later psychologists, is b}' no means gcncrallx accepted. Some 

 argue that the estimation of distance by the eye, is, as Berkeley 

 said, a result of suggestion and experience, but that visual experi- 

 ence alone is adequate, and this Berkeley denied. It is further 

 maintained that depth feeling is just as optical in its nature as 

 either hight or breadth, and that in the absence of motion of the 

 body, or any part of it, toward or away from objects observed, the 

 movement of the objects themselves may be substituted, with simi- 

 lar experience resulting. 



Persons blind from birth and acquiring their sight in later years, 

 have thus at first experienced distance by touch, and afterwai'd 

 both by touch and sight. As these persons (about twelve cases 

 having been reported) gciwra/ly maintain that all objects seemed to 

 be, when first seen, in one plane near the globe of the eye, and 

 that optical perception of their distance was learned by "associa- 



(109) KAN. UNIV. QU.\R., VOL. V, NO 2. OCTOBER, 1896. 



