Abstract-The apparent ilt from vertical has been examined for vertical sinusoidal gratings in the presence of an inducing grating which was tilted 12 ’ from vertical. The amount of apparent tilt depended on the contrast of the test grating. At high test contrasts, the grating appeared to be tilted about 2 ” clockwise; at low contrasts, near threshold. there was little or no apparent tilt. If the inducing grating and test grating were not contiguous but were separated by about 0.4’. there was no apparent tilt at any test contrast. The detection threshold for the test grating was elevated by the inducing grating only when the whole of the test grating was close to the inducing grating. It is argued that these results can be explained if there is an inhibitory interaction between detectors responding to similar orientations and subserving similar parts of the visual field. INTRODUflION Viewing a grating for a few seconds may cause a subsequently-viewed grating in the same region of the visual field to appear distorted in several ways. First, its apparent orientation may be changed the tilt after-effect (Vernon, 1934; Gibson and Radner, 1937). Second. its apparent spatial-frequency may be changed, the spatial-frequency after-effect (Blake
