The properties of surround antagonism elicited by spinning windmill patterns in the mudpuppy retina.

1. A truncated spinning windmill pattern, illuminating only the receptive field surround, shown previously to activate amacrine cells, was used to elicit activity at the inner plexiform layer and to reduce the response of ganglion cells to test flashes at the receptive field centre. 2. The spinning windmill pattern reduced the ganglion cell response over its entire graded range by a fixed amount, and reduced the domain of test intensities required for graded activity. 3. The windmill effect was graded for windmill intensities over a domain of about 1000 to 1. The effect was constant for windmill velocities from about 0.05 to 0.5 rev/sec, and diminished beyond these velocities. 4. The windmill effect varied with windmill area as though each retinal point contributed to the reduction of ganglion cell response with a weighting which fell exponentially from the receptive field centre. The space constant was 0.35 mm. 5. The graded reduction in ganglion cell response was closely correlated with the graded increase in amacrine cell activity when the windmill intensity, area, and velocity were varied. It is inferred that amacrine cells, activated by the windmill, act to reduce the response range of the ganglion cells, primarily through a feed-forward pathway.