Spatiotemporal Characteristics of the Stereoscopic Anisotropy.

Purpose: There is a well-known orientation anisotropy in stereovision, where disparity thresholds for sinusoidal corrugations of low spatial frequencies are much higher for vertical than for horizontal orientations. While previous research has indicated that the visual system responds more rapidly to horizontal than vertical slanted surfaces, the spatiotemporal characteristics underlying the stereoscopic anisotropy have not been thoroughly studied. This study aims to quantify the anisotropy across a range of spatial and temporal frequencies. Methods: We measured disparity thresholds for vertical and horizontal sinusoidal corrugations across different spatial (from 0.05 to 0.8 cpd) and temporal frequencies (from 0 to 8 Hz). To interpret the data, we fitted a spatiotemporal cross-correlation model (that approximates the disparity-energy calculation in V1). The model included a shift parameter to capture the differences in sensitivity between orientations. Results: Disparity thresholds as a function of temporal frequency revealed a low-pass shape. Across all conditions, thresholds were consistently higher for vertical than for horizontal corrugations. The degree of anisotropy decreased with increasing spatial frequency and was strongest at lower spatial frequencies. Model fits revealed similar spatial and temporal weighting functions for both orientations, with a global vertical shift accounting for the reduced sensitivity observed for vertical corrugations. Conclusions: This study provides a systematic characterization of the spatiotemporal properties of stereoscopic anisotropy. Disparity thresholds were consistently higher for vertical than for horizontal corrugations, particularly at low spatial frequencies and for all temporal frequencies. Our simulation results indicate that the anisotropy can be captured by a global vertical shift in sensitivity, while the spatiotemporal disparity processing is similar for both orientations.