Abstract
1. 57 on- and off-center units in the cat's optic tract were studied after 30 min of dark adaptation by stimulating the receptive field periphery with flashing annuli. 49 reacted with center-like responses, 4 did not respond and 4 offcenter cells showed weak antagonistic surround responses. 54 showed antagonistic surround responses when a steady adapting spot of suitably chosen luminance was directed on to the center of the fields. 2. With equal stimulation of the surround the total flux of the steady center spot determined the condition of reversal from center to surround responses. 3. Under the condition of reversal the on-going firing rate was also affected. Reversal of responses was also observed with short stimulus durations (≥ 50 msec). 4. The recovery time from reversed responses to center-like responses was less than I min after darkening the center again. 5. With increasing center spot luminance, the latency of the center-type excitatory responses from on- and off-center neurones remained approximately constant, whereas the latency of the surround excitatory response was decreased. 6. Neuronal mechanisms are considered which give rise to excitatory responses in total darkness and inhibitory responses if neighbouring parts of the retina are light adapted. The equivalence of light adaptation and lateral inhibition as well as the effects of stray light are discussed.
Published Version
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