SECTION X 

 VISUAL JUDGMENTS 



LOCALISATION AND PROJECTION. Much discussion has been 

 wasted on the question why we see things upright while the images 

 on our retina are inverted. The answer is a simple one. We do not 

 look at nor are we conscious of the image on our retina. When 

 we say that we see anything we are not expressing merely a 

 sensation, but we are giving an interpretation of certain sensations 

 in the light of long experience which has involved a large number 

 of sensations besides that of vision. Thus a new-born child sees, 

 i.e. receives images on its retina which excite impulses in the 

 brain, but it is unable to interpret anything that it sees. In the 

 first few months there is indeed no connection between the visual 

 sensations and eye movements ; it is only about the third month 

 after birth that the child will follow a lighted candle or bright object 

 with its eyes, and this association of ocular movements with 

 retinal impressions gradually extends also to many other movements. 

 The continual and at first apparently aimless movements of the 

 infant bring in a flood of muscular and tactile impressions which only 

 after many trials are recognised as corresponding with sensations 

 arriving from the eyes. It at first finds that with the right hand it 

 can touch objects lying on the right side of the field of vision. It 

 becomes conscious therefore, not of the left side of its retina, but of a 

 series of objects which have distinct relations to its right hand, and of 

 a certain thing seen outside itself. The projection and localisation of 

 visual impressions are therefore not intuitive or innate qualities 

 attached to stimulation of each point of the retina, but are the result 

 of experience, the testing and comparing of visual sensations with 

 tactile and muscular sensations from all parts of the body. From these 

 experiences we learn to associate stimulation, say, of the right side 

 of the retina with the presence of objects lying in front of and to 

 the left of the body, and to project our visual sensations in this 

 direction. If, for instance, we press the finger, with closed eyelids, on 

 the outer side of the right eyeball, a luminous ring, or phosphene, 

 will be seen apparently towards the left, i.e. the region whence the 

 pressed-upon part of the retina will be normally stimulated by rays 

 of light. 



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