Investigating Human Visual Sensitivity to Binocular Motion-in-Depth for Anti- and De-Correlated Random-Dot Stimuli.

Martin Giesel,Marina Bloj,Alex Wade,Julie Harris

doi:10.3390/vision2040041

Abstract

Motion-in-depth can be detected by using two different types of binocular cues: change of disparity (CD) and inter-ocular velocity differences (IOVD). To investigate the underlying detection mechanisms, stimuli can be constructed that isolate these cues or contain both (FULL cue). Two different methods to isolate the IOVD cue can be employed: anti-correlated (aIOVD) and de-correlated (dIOVD) motion signals. While both types of stimuli have been used in studies investigating the perception of motion-in-depth, for the first time, we explore whether both stimuli isolate the same mechanism and how they differ in their relative efficacy. Here, we set out to directly compare aIOVD and dIOVD sensitivity by measuring motion coherence thresholds. In accordance with previous results by Czuba et al. (2010), we found that motion coherence thresholds were similar for aIOVD and FULL cue stimuli for most participants. Thresholds for dIOVD stimuli, however, differed consistently from thresholds for the two other cues, suggesting that aIOVD and dIOVD stimuli could be driving different visual mechanisms.

Highlights

Motion-in-depth refers to a movement towards or away from an observer
Deviating from Czuba et al [35], we aimed to deliver noise equivalently in each of the stimulus variants, i.e., the correlational properties of the noise dots differed between the different types of stimuli: The noise dots for FULL cue stimuli were correlated between the eyes, anti-correlated for aIOVD stimuli, and de-correlated for dIOVD stimuli
While the changes in disparity in random-dot stereograms might be equivalent to those found in real-world motion-in-depth, the full-field inter-ocular velocity differences (IOVD) signal, because looming cues have been removed, generates a set of motion-in-depth vectors that would be consistent with complex non-rigid motion in the real world [16]

Summary

Introduction

Motion-in-depth refers to a movement towards or away from an observer. The detection of motion-in-depth, the discrimination of its direction (i.e., towards or away), and the estimation of its speed are crucial for our survival. When an object moves towards or away from us, the images it projects on the retinas of the two eyes vary systematically with the movement These variations can be used by the visual system to detect both the direction and speed of motion in depth. For a point moving directly towards an observer in depth, the corresponding points in the retinal images move in opposite directions in the two eyes. Both monocular and binocular cues contribute to the perception of motion-in-depth in Vision 2018, 2, 41; doi:10.3390/vision2040041 www.mdpi.com/journal/vision

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