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. 



658 



