INHIBITORY INTERACTION IN THE RETINA 



253 



B 

 alone 



46 



1.5 sec. 



Fig. 1 1. Oscillograms of action potentials recorded simultaneously from two optic 

 nerve fibers, showing the discharge of nerve impulses when the respective omma- 

 tidia in which these fibers arose were illuminated separately and together. The 

 numbers on the right give the total number of impulses discharged in the period 

 of 1 • 5 sec, for the respective cases. The inhibitory effect on A, 53^3, is to be asso- 

 ciated with the concurrent frequency of B, 35 ; likewise the effect on B, 46-35, is to 

 be associated with the concurrent frequency of A, 43 (see text). Time in ' sec. 

 (From Hartline and RathiT, 1957.) 



ommatidium in the interacting set, it is evident that a closely-knit inter- 

 dependence characterizes the activity of receptor units in this eye. 



This crucial feature of the inhibitory interaction was unrecognized by us 

 in the early years of our work. We were puzzled by confusing and seemingly 

 contradictory results: spatial summation of inhibitory influences seemed to 

 depend unpredictably on the location of the retinal regions with respect to 

 one another and to the receptor on which the summating action was being 

 tested; inhibitory effects could not be consistently related to intensities of 

 retinal illumination. Only when we recognized that the inhibition exerted by 

 a receptor depended on the level of its activity rather than on the level of 

 its stimulation, could we make sense out of our results. When we recorded 

 from two interacting ommatidia simultaneously, using diff"erent intensities 

 on them, in various combinations, it becaine apparent that the decrement of 



