Abstract

We used temporal forced choice to estimate threshold contrast for a test grating in the presence of a second, pedestal grating. Both gratings had the same spatial frequency, but they were either in-phase, 180° out of phase, or 90° out of phase. Mean luminance varied over 3 log units. The main finding is that luminance and pedestal contrast trade off in determining sensitivity, so that only their product, pedestal amplitude, uniquely determines sensitivity (unless pedestal contrast is close to threshold, in which case luminance has a greater effect than does pedestal contrast). This means that contrast gain control and luminance gain control have similar properties and might share the same mechanism. We also found that the relative phase of pedestal and test grating has relatively little effect and that temporal modulation of the test grating greatly decreases the effects of steady pedestals.

© 1992 Optical Society of America