Abstract

Data were analyzed from a previous study¹ of psychophysical thresholds to spatiotemporal wiggle of lines in lateral displacement (monocular viewing) and in stereopsis (dichoptic viewing of the same lines with counterphase disparity wiggle). The threshold surfaces were not separable into the product of a spatial and a temporal frequency function. The aim of the present analysis was to determine whether, like spatiotemporal contrast thresholds, the data could be well described as the sum (or difference) of two spatiotemporally separable components. Singular value decomposition showed that two components accounted for both lateral and disparity surfaces to an accuracy of ~95%. We optimized separable components with the constraint that each component was simple in that it had only positive sensitivity and that it minimized the second component magnitude. These constraints revealed a similar excitatory component for both displacement and disparity domains. The second component was inhibitory with reduced sensitivity for low frequencies in both space and time, as for contrast-domain inhibition. The inhibitory component for disparity, however, had a purely spatial tuning, independent of temporal frequency. This behavior is reminiscent of that for stereomovement suppression² and suggests that lateral and disparity thresholds are processed by independent neural mechanisms.

© 1992 Optical Society of America