Binocular disparity modulation sensitivity to disparities offset from the plane of fixation

Corrugated disparity gratings mounted on depth pedestals were portrayed with random-dot stereograms in order to measure the cyclopean disparity modulation transfer function at various offsets from fixation. We found changes in both sensitivity as well as shape as the magnitude of the pedestal varied. Threshold disparity modulation amplitude curves, plotted as a function of corrugation frequency, became narrower and shifted toward lower frequencies as pedestal size increased. There were stable asymmetries between sensitivities to crossed and uncrossed pedestals; these could be accounted for by assuming each observer to have a constant fixation disparity on the order of 5' of arc.