Stereopsis, spatial frequency and retinal eccentricity.

Stereoscopic depth discrimination thresholds increase with retinal eccentricity and distance from the horopter. However, in contrast to spatial resolution, the effects of spatial frequency on stereo-thresholds in the periphery are unknown. For spatial vision, it is generally assumed that the retina is comprised of a series of overlapping spatial filter mechanisms and that there is a commensurate increase in spatial scale as a function of retinal eccentricity. If the same holds true for mechanisms sensitive to stereoscopic depth, then stereo-thresholds for low spatial frequency stereoscopic stimuli may remain relatively invariant across the visual field, while thresholds for relatively high spatial frequency stimuli would increase. To further understand the role of the disparity sensitive mechanisms involved in depth discrimination, increment depth discrimination thresholds for both crossed and uncrossed disparities were measured as a function of eccentricity for retinal locations up to 10.0 deg along the horizontal meridian. We found that stereoscopic depth discrimination thresholds, as a function of distance from the horopter, increased in an exponential manner irrespective of spatial frequency. Stereo-thresholds also increased as a function of retinal eccentricity, however, the rate of increase depended on the spatial frequency composition of the stimuli. Best stereo-thresholds for stimuli composed of low spatial frequencies remained relatively invariant for retinal eccentricities up to 10.0 deg, while thresholds for the high spatial frequency stimuli increased with eccentricity.