First and second-order contributions to surface interpolation

Comparisons of 1st- and 2nd-order stereopsis have typically employed isolat ed, or local, narrow-band targets. While these experiments have revealed a great deal about the distinction between these two types of processing, suc h stimuli are rare in the natural environment. Instead, local disparity sig nals are more likely to be part of extended surfaces that vary smoothly in depth. The aim of the experiments presented here is to determine the relati ve contribution of 1st- and 2nd-order stereopsis to the perception of depth -modulated surfaces. Stereothresholds were measured under a range of condit ions designed to isolate either 1st- or 2nd-order processing. The results d emonstrate that while 2nd-order stereopsis provides local depth estimates f or individual texture elements, 1st-order processing is essential to the gl obal interpolation of those estimates across surfaces. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.