Adaptation Mechanisms in Spatial Vision II: Flash Thresholds and Background Adaptation
Philip T. Kortum and Wilson S. Geisler

To examine how the mechanisms of light adaptation affect spatial pattern vision, contrast detection thresholds were measured for sinusoidal (increment-Gabor) probes on flashed backgrounds in the presence of steady adapting backgrounds. The thresholds for all spatial frequencies (1-12 cpd), flashed-background intensities (dark to 4 log td) and adapting-background intensities (dark to 4 log td) were adequately described by a simple model consisting of a compressive nonlinearity (a modified Naka-Rushton function), a subtractive adaptation factor, and multiplicative adaptation factor. For all five subjects, the compressive nonlinearity was found to vary systematically with spatial frequency; for all but one subject, the subtractive and multiplicative factors were found to be relatively constant. This research was supported by NIH grant EY02688 and AFOSR grant F49620-93-1-0307 to WSG.