Abstract

Studies of upper and lower stereoscopic thresholds demonstrate that at 2.5 c/deg the thresholds abruptly change their behavior; below this frequency they fit power functions of wavelength (e.g., power 1 for static depth discrimination task and 1/2 for dynamic case). Dichoptic spatial frequency tuning studies have been interpreted as revealing a set of narrowband channels in this low frequency domain. However, data on the monocular masking of narrowband stereoscopic targets indicate that the sensitivity of channels below 2.5 c/deg is negligible. We therefore made the alternative assumption that there are channels only above 2.5 c/deg and that the rise of thresholds for low frequencies is a result of the drop in the effective contrast response of the 2.5 c/deg channel at low frequencies. The dichoptic tuning functions for low frequencies would also then be explained by contrast effects. The dichoptic difference in mean spatial frequency, which is varied for the tuning experiments, produces a difference in effective contrast between the eyes, which, in turn, causes the observed deterioration in sensitivity. Based on these ideas we propose a model that provides a consistent explanation for a large set of experimental data.

© 1992 Optical Society of America