First and second-order contributions to surface interpolation

Comparisons of 1st- and 2nd-order stereopsis have typically employed isolated, or local, narrow-band targets. While these experiments have revealed a great deal about the distinction between these two types of processing, such stimuli are rare in the natural environment. Instead, local disparity signals are more likely to be part of extended surfaces that very smoothly in depth. The aim of the experiments presented here is to determine the relative contribution of 1st- and 2nd-order stereopsis to the perception of depth-modulated surfaces. Stereothresholds were measured under a range of conditions designed to isolate either 1st- or 2nd-order processing. The results demonstrate that while 2nd-order stereopsis provides local depth estimates for individual texture elements, 1st-order processing is essential to the global interpolation of those estimates across surfaces.