Abstract
Binocular differencing of spatial cues required for perceiving depth relationships is associated with decreased sensitivity to the corresponding retinal image displacements. However, binocular summation of contrast signals increases sensitivity. Here, we investigated this divergence in sensitivity by making direct neural measurements of responses to suprathreshold motion in human adults and 5-month-old infants using steady-state visually evoked potentials. Interocular differences in retinal image motion generated suppressed response functions and correspondingly elevated perceptual thresholds compared to motion matched between the two eyes. This suppression was of equal strength for horizontal and vertical motion and therefore not specific to the perception of motion-in-depth. Suppression is strongly dependent on the presence of spatial references in the image and highly immature in infants. Suppression appears to be the manifestation of a succession of spatial and interocular opponency operations that occur at an intermediate processing stage either before or in parallel with the extraction of motion-in-depth.
Highlights
Binocular differencing of spatial cues required for perceiving depth relationships is associated with decreased sensitivity to the corresponding retinal image displacements
Our approach builds on these results and prior work with the visually evoked potential (VEP) on motion processing[27,28] and spatial integration[29,30,31] to systematically explore neural responses to motion and disparity using minimally complex scene structures containing regions defined by motion, disparity, or both
VEPs provide direct neural measures that can bridge the nearthreshold regime used in the psychophysical literature and the suprathreshold regime used in the primate electrophysiology literature, allowing us to test previously proposed computational mechanisms for binocular motion processing[24,25,32]
Summary
Binocular differencing of spatial cues required for perceiving depth relationships is associated with decreased sensitivity to the corresponding retinal image displacements. The visual system can read out the binocular disparity of an object relative to the fixation plane and track how this information varies over time (change of disparity over time or CDOT) Another possibility is to compare object velocity from each monocular image (interocular velocity difference or IOVD). We take advantage of the fundamental asymmetry in retinal stimulation caused by the lateral separations of the eyes and compare stimuli with horizontally displaced motion signals that are ecologically relevant to MID, and to stimuli with vertically displaced motion signals that are not This allows us to separate neural responses adapted to MID from those that support more generic imageprocessing functions. In a subset of our experiments, we collect both neural and psychophysical data at the same time, and directly relate brain responses to perception
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