302 PROCEEDINGS OP THE ACADEMY OF [1886. 



REVERSE VISION. 

 BY CHARLES MORRIS. 



The fact that we perceive objects in their correct position, 

 while their impression upon the retina is a reversed one, forms a 

 problem which has given rise to much speculation, often unprofit- 

 ably metaphysical, in the effort to explain it. None of these 

 theories of the older writers now remain current. More modern 

 authors give explanations which are little more satisfactory. 

 Giraud Teulon says : " The retina sees or localizes objects where 

 they are; that is what we call ' erect;' if the picture be reversed 

 it is a mere matter of geometry." Helmholtz says: "Our 

 natural consciousness is completely ignorant even of the exist- 

 ence of the retina and of the formation of images ; how should 

 it know anything of the position of images formed upon it ? " 

 It cannot be claimed that these remarks are explanations, and we 

 may proceed to the more elaborate theory advanced by LeConte, 

 in his work on " Sight." He remarks that " the retinal image 

 impresses the retina in a definite way. This impression is then 

 conveyed by the optic nerve to the brain, and determines changes 

 there. . . . And then the brain or the mind refers or projects 

 the impression outward into space as an external image, the sign 

 or facsimile of an object producing it." He proceeds: "The 

 law may be thus stated : When the rays from any radiant strike 

 the retina, the impression is referred back along the ray line 

 {central ray of the pencil) into space, and therefore to its proper 

 placed 



It cannot be said that his arguments are suflSicient to establish 

 this theory. That we mentally refer an impression to the nerve 

 extremity that received it is unquestionable, and where a limb 

 has been lost, impressions seem to be referred to the location of 

 the original nerve termination. But this is very probably a 

 result of long-continued hereditary influences, through which 

 each nerve becomes adapted to give a mental picture of the loca- 

 tion of its impressions, and continues to do so even if touched 

 at some intermediate point. In the case of sight, no localized 

 reference to the nerve extremity exists. In this sense the source 

 of our impression seems external to the body. And yet this is 

 in all probability equally a result of hereditary accommodation. 



