SCALE SELECTION FOR 2ND-ORDER (NONLINEAR) STEREOPSIS

In addition to the conventional luminance spatial frequency-dependent, disparity processing mode, there is a second-order luminance spatial frequency-independent type of processing available to the stereoscopic system, Here we use gaussian-enveloped, amplitude-modulated grating p atches to determine how the stereoscopic system responds to the presen ce of two sources of second-order disparity information at different s cales when there is no disparity information available via the convent ional luminance-based system. In the first experiment we show that the stereoscopic system uses the disparity signal provided by the stimulu s envelope, even though it is at a coarser scale than that provided by the amplitude modulation (AM), We then demonstrate that if the stimul us envelope is degraded via blurring, or if it is fixed at zero dispar ity, then performance depends on the finer-scale AM disparity signal, To show that the stereoscopic system uses the disparity signal provide d by the AM we extend the carrier grating outside the borders of the A M stimulus, thereby making the boundary of the patch less discernible, Results obtained using this stimulus suggest that when two sources of second-order disparity information are present within the same stimul us (i.e., with no reliable luminance-based disparity signal available) , the disparity signal provided by the coarser-scale contrast envelope vetoes the finer-scale disparity signal, The coarse-scale disparity i nformation dominates as long at it provides an adequate disparity sign al, When it is degraded, however, the finer-scale signal takes precede nce, (C) 1997 Elsevier Science Ltd.