LINEAR AND NONLINEAR TRANSPARENCIES IN BINOCULAR VISION

When the product of a vertical square-wave grating (contrast envelope) and a horizontal sinusoidal grating (carrier) are viewed binocularly with different disparity cues they can be perceived transparently at d ifferent depths. We found, however, that the transparency was asymmetr ic; it only occurred when the envelope was perceived to be the overlay ing surface. When the same two signals were added, the percept of tran sparency was symmetrical; either signal could be seen in front of or b ehind the other at different depths. Differences between these multipl icative and additive signal combinations were examined in two experime nts. In one, we measured disparity thresholds for transparency as a fu nction of the spatial frequency of the envelope. In the other, we meas ured disparity discrimination thresholds. In both experiments the thre sholds for the multiplicative condition, unlike the additive condition , showed distinct minima at low envelope frequencies. The different se nsitivity curves found for multiplicative and additive signal combinat ions suggest that different processes mediated the disparity signal. T he data are consistent with a two-channel model of binocular matching, with multiple depth cues represented at single retinal locations.