Visual adaptation to patterns containing two-dimensional spatial structure

Abstract

Adaptation experiments have been carried out using gratings periodic in two dimensions. The threshold elevation effect was measured using such patterns both as test gratings and as adaptation gratings. It is shown that the threshold elevation effect is selective for the length of bars in the gratings, the maximum effect occurring when the bar length in the adaptation grating is the same as that in the test grating. This selectivity holds for bar lengths less than about three times the bar width, whereas for longer bars, the threshold elevation effect is independent of the bar length. It is suggested that there are two populations of mechanism; one population which is length selective and responds to bars with length to width ratio less than three, and another population which is not length selective and responds to bars with length to width ratio greater than three. The orientation selectivity is calculated for the latter population of mechanism and shown to be in agreement with experimental data on the orientation selectivity of the threshold elevation effect for linear gratings.