Abstract
Binocular disparities allow us to perceive the 3D layout and structure of objects even in the absence of other cues. Remarkably, although the disparity field is generally sparse, continuous surfaces appear smooth. This suggests that some interpolation process is used by the visual system to fill in the gaps of the discrete disparity input signal. Previous work has shown that continuous shading gradients may be leveraged in this process by cooperatively “filling in” unspecified gaps where no disparity exists in sparse disparity fields. We systematically tested observers’ ability to measure unspecified regions of stereoscopically presented surfaces using a probe adjustment task. In this task, observers adjusted the binocular disparity of a small dot until it appeared to rest on the surface of a 3D cosine bump. Our aim was to evaluate whether conflicting shading information, though providing no disparity information, would influence how observers interpolate the surface within the unspecified regions. Importantly, we controlled what disparity information was available during different surface conditions, including disparity-only, shading-only, and combined disparity and shading. The disparity field in both the disparity-only and combined-cue condition specified a 3D bump with its peak centered on the image plane. Two different conflicting shading patterns were either presented alone (shading-only) or combined with the disparity surface (combined-cue): one generated from a cosine bump with its peak shifted upwards on the image plane, and one with its peak shifted downwards on the image plane. This created regions of predicted positive and negative depth bias. Strikingly, we found highly reliable depth biases in the combined-cue stimulus predicted by the conflicting shading information, which could not be explained by independent combination of disparity and shading. Instead, we find evidence of a cooperation between disparity and shading, where smooth shading information effectively warps the interpolation of the disparity field.