Disparity modulation sensitivity for narrow-band-filtered stereograms.

Stereo thresholds for 84% correct detection of sinusoidal disparity corrugations depicted by narrow-band-filtered random dot stereograms were determined for surfaces as a function of (i) luminance center spatial frequency and (ii) disparity modulation frequency. In addition, supra-threshold depth matching functions for two amplitudes of peak-to-trough depth were determined using similar stimuli. Disparity thresholds followed a U-shaped function when plotted against luminance centre spatial frequency from 1 to 8 c/deg. The threshold functions for the three highest corrugation frequencies (ranging from 0.25 to 1 c/deg) formed a single family with a similar bandpass shape and a peak sensitivity at ca 4 c/deg. At the lowest frequency of depth modulation (0.125 c/deg) the shape of the luminance spatial frequency threshold function showed a reduced sensitivity to depth modulations when portrayed by patterns with high luminance centre frequencies (8 c/deg). The similarity of the threshold functions reveals luminance and corrugation frequency to be largely independent dimensions. The finding that the functions are not identical provides some evidence to support a weak luminance spatial frequency selectivity in stereoscopic channels tuned to corrugation frequency.