The influence of the background on the generation of inhibition

The conditions leading to the generation of propagating inhibition have been investigated. The use of elementary point flashes as probes makes it possible to detect both the site and the time of inhibition with a high precision. The background luminance is found to influence the extent of inhibition. When no background illumination is present, no inhibition is detected. When only part of the background is illuminated, inhibition is sometimes found, and sometimes not. Experiments involving systematic buildup and breakdown of a background luminance field showed that inhibition only occurs when luminance is present within the range within which the inhibition effects operate (about 25 min of arc).