Marathon adaptation to spatial contrast: saturation in sight.

The contrast thresholds for detecting a 6.0 c/deg vertical sinusoidal test grating were tracked during and after 3 hr inspection of a high-contrast adapting grating of the same spatial frequency and orientation. Log contrast threshold increased linearly with log adaptation time, attaining a final stable value after approximately 30 and 60 min of adaptation for the two subjects tested. The recovery function was likewise linear on double logarithmic axes. The results further suggest that adaptation beyond the saturation point had no influence on the subsequent rate of recovery.