STRUCTURE OF THE RETINA 45 



the individual bars subtend, in various experiments, 0.1 degree, 0.5 de- 

 gree, 1 degree, 2 degrees, etc. In response to a movement of the 2-degree 

 bars, the insect responds by moving away. When the 0.5-degree bars were 

 used, the insect made no response, thus showing that the fineness of the 

 bars was such that the images overlapped and looked grey to him; he 

 could perceive no motion in these circumstances. 



The human eye can be studied in a similar way, and the resolution of 

 0.01 degree corresponds well with the angle subtended at the lens by 

 neighboring retinal elements. To give an idea of what these numbers 

 mean, a ringer at arm's length subtends about one degree. Thus an insect 

 can just make out the individual fingers of a man one yard away; a 

 human can make them out about 100 yards away. 



It should be realized that the experiments described in this chapter 

 were done 20 years ago and that much work of a far more sophisticated 

 nature has been done in the intervening years. Also during that time, 

 enormous success has been achieved in studying the biochemistry of 

 vision. Some biophysicists feel that studies of vision will provide the 

 most direct route to an understanding of the nerve interplay which goes 

 by the name of neurophysiology. Accordingly, the neurophysiology of 

 vision is emerging as one of the most important and most exciting areas 

 of research today. 



