Motion in depth cued by chromatic interocular velocity differences and changing disparity

Motion in depth cued by chromatic interocular velocity differences and changing disparity A Wade, J Jordan, M Kaestner, P Shah
Psychology, University of York, United Kingdom Contact: wade@wadelab.net
Motion towards and away from an observer generates two related but separable visual cues. The first is the temporal derivative of the retinal disparity: the rate at which the three dimensional position of the object is changing, called ‘changing disparity’ (CD). The other cue is the disparity of the temporal derivative of the retinal position of the object in each eye: the interocular velocity difference (IOVD). We describe a series of experiments measuring sensitivity to motion in depth using coherence thresholds for dense random dot stereograms (RDS). We examined the effect of changing the motion in depth cue (CD vs IOVD with both decorrelated and anticorrelated dots), and the chromaticity of the individual elements (achromatic, isoluminant red/green and S-cone isolating). Isoluminant chromatic signals are generally considered to contribute very little to both motion processing and stereo depth mechanisms. Surprisingly therefore, we report that coherence thresholds for isoluminant CD and IOVD stimuli are robust and similar to those for achromatic stimuli. We hypothesize that motion in depth may engage cortical systems that do not exhibit the usual magnocellular pathway insensitivity to isoluminant color.

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