The effects of adaptation to gratings on the perceived orientation of single lines

Subjects were adapted for 45 s to a 5 cycle per degree grating, tilted 10° from the vertical, and at one of four levels of luminance contrast. Estimates of the slope of the grating, or of a single line which replaced the grating, were obtained before and after the period of adaptation by the subject's setting of a single reference line which was located 3° from the edge of the grating. In Experiment I the fixation area was at the centre of the grating, so that half of the grating fell on each retinal hemifield. The reference line was set to a tilt further from the vertical following the period of adaptation, indicating either a change in the apparent orientation of the grating or the reference line. In Experiment II, where the fixation area was midway between the grating and the reference line, so that line and grating appeared in different hemifields, settings indicated no change in the tilt of the grating. In Experiment III, where the fixation area was again midway between grating and setting line, but where the grating was replaced by a single line after the adaptation period, settings indicated that the line had decreased in apparent tilt. The results of the three experiments indicate that while gratings either do not normalize or do so to an insignificant extent they produce a substantial amount of normalization on a single line. Comparison of the results of Experiments I and II shows that spread of this effect outside the directly adapted area is less across the naso-temporal division of the retina than within the same hemifield.