Spatial-frequency and contrast tuning of the transient-stereopsis system

Abstract

The tuning of the transient-stereopsis system to luminance contrast and spatial-frequency (SF) was investigated with narrow-band gabor targets with a constant sigma of 1 degree. They were presented for brief (140 ms) durations and subtended a large (6 degrees) disparity. When dichoptic gabor stimuli were matched in SF (0-5 cpd), transient stereo performance was either uniform across SF or greater at frequencies below 1 cpd. When dichoptic stimuli had unmatched SF (0.5 + 0-5 cpd) and matched contrast (100%), stereo performance was impaired below that of the matched SF condition. Stereo performance with matched SF at 0.5 cpd was impaired when contrast of one eye's image was reduced, demonstrating a contrast-paradox effect (i.e. contrast tuning) for transient stereopsis. Performance with three dichoptic unmatched SF conditions (0.5 and 1.0 cpd; 0.5 and 5.0 cpd; 1.5 and 3.5 cpd) was improved when the contrasts of the low SF gabor was reduced while holding the contrast of the high SF gabor constant at 100%. However stereo performance was not improved by reducing the contrast of a high SF gabor (3.5 cpd) while holding the contrast of the lower SF gabor (1.5 cpd) constant at 100%. We interpret these findings as indicating that transient-stereopsis performance is mediated by a single spatial-channel that has low-pass spatial-frequency sensitivity and which compares the ocular based signals prior to binocular combination so that signals that are not balanced in terms of their strength lead to a weaker binocular signal, as per the model proposed by Kontsevich and Tyler (Vis Res 1994; 3417:2317-2329) for sustained stereopsis.

Orientation-Specific Computation in Stereoscopic Vision

“…1 B, right). This result is understandable if these thresholds are measures of the observer's sensitivity either to the absolute disparity of the grating or to the relative disparity between the carrier of the grating patch and its Gaussian-windowed contrast envelope (Hess and Wilcox, 1994;Schor et al, 1998;Langley et al, 1999;McKee et al, 2004), the disparity of which was fixed at zero (or perhaps between the carrier and other, more distant reference stimuli, such as the edges of the monitor). If the observer was more sensitive to any of these disparities than to the relative disparity between the two carriers, threshold would depend little on the grating orientation difference.…”

“…Perhaps we are unable do so in the absence of intermediate orientations in the scene to serve as common reference stimuli. Alternatively, second-order stimulus features (Hess and Wilcox, 1994;Schor et al, 1998;Langley et al, 1999;McKee et al, 2004) might play this role in naturalistic scenes. Another possibility is that normalization does occur, but only among the spatially overlapping components of a single object, such as the components of the plaids used here.…”

How to use individual differences to isolate functional organization, biology, and utility of visual functions; with illustrative proposals for stereopsis

“…More recently, Clifton Schor and colleagues have conducted a systematic characterization of our sensitivity to depth from transient and sustained disparity (Schor et al, 2001(Schor et al, , 1998(Schor et al, , 1984Edwards et al, 2000Edwards et al, , 1999aPope et al, 1999). These studies have shown different 1) spatial tuning, 2) tendency to depth-alias, 3) orientation tuning, 4) sensitivity to spatial envelope size, and 5) tolerance for opposite polarity, for long vs. short duration depth stimuli.…”

Neural Basis for Stereopsis from Second-Order Contrast Cues

“…Several mechanisms have been suggested to reduce these false matches and compute depth correctly, such as coarse-to-fine processing (Marr and Poggio, 1979) and pooling of disparity sensor activities over positions, multiple spatial frequencies, and orientations Qian and Zhu, 1997). For textured surfaces, coarse-scale disparity information is effectively obtained using the contrast envelope Hess, 1995, 1997;Schor et al, 1998). Therefore, the notion of coarse-to-fine and multichannel pooling probably should be extended to include the additional disparity information originating from the envelopeprocessing pathway.…”

“…Previously, a substantial number of psychophysical studies investigated binocular processing of contrast-envelope cues (Hess and Wilcox, 1994;Wilcox and Hess, 1995Schor et al, 1998;Edwards et al, 1999Edwards et al, , 2000Langley et al, 1999;McKee et al, 2004). These studies have shown that we are able to perceive depth based purely on binocular disparities of contrastenvelope cues and suggested that such stereopsis is mediated by nonlinear mechanisms that are distinct from that for extracting luminance-based cues.…”