Interocular contrast difference drives illusory 3D percept

Abstract

Any processing delay between the two eyes can result in illusory 3D percepts for moving objects because of either changes in the pure disparities over time for disparity sensors or by changes to sensors that encode motion/disparity conjointly. This is demonstrated by viewing a fronto-parallel pendulum through a neutral density (ND) filter placed over one eye, resulting in the illusory 3D percept of the pendulum following an elliptical orbit in depth, the so-called Pulfrich phenomenon. Here we use a paradigm where a cylinder rotating in depth, defined by moving Gabor patches is presented at different interocular phases, generating strong to ambiguous depth percepts. This paradigm allows one to manipulate independently the contrast and the luminance of the patches to determine their influence on perceived motion-in-depth. Thus we show psychophysically that an interocular contrast difference can itself result in a similar illusory 3D percept of motion-in-depth. We argue that contrast, like luminance (ND filter) can modify the dynamics of visual neurons resulting in an interocular processing delay or an interocular velocity difference.

Interocular Differences in Spatial Frequency Influence the Pulfrich Effect

“…In this paper, we report PSEs as a function of either the size or spatial frequency ratio of the Gabor elements shown to the left and right eye. We conducted linear regression as in previous studies [5,26] using RStudio [27]. We performed a two-tailed Wilcoxon test to compare the slopes of PSEs as a function of frequency and size ratio.…”

“…When the phase shift is 0 • , the depth percept appears ambiguous, whereby Gabor elements are seen moving laterally in the plane of the screen. This figure has been adapted from Reynaud and Hess, 2017 [5]. (B) A psychometric function of the perceived rotation direction as a function of the interocular phase shift between the eyes from Subject 7.…”

“…It occurs when one eye is delayed relative to the other eye ( Figure 1A). Interocular delay can be caused by interocular differences in either luminance or contrast [2][3][4][5][6]. Hence, placing a neutral density filter over one eye produces an interocular luminance difference, delays the processing of said eye, and induces the Pulfrich effect.…”

“…In this study we investigate independently how spatial frequency and size of stimuli influence interocular delay using a novel psychophysical task based on the Pulfrich effect [5]. Reynaud and Hess (2017) introduced this novel task, in which dichoptically presented stimuli consisting of bandpass microelements differ in one stimulus parameter, such as contrast or luminance [5]. The task enables one to individually analyze the influence of a stimulus parameter on the interocular delay.…”

Monovision and the Misperception of Motion

“…1A). The effect occurs because the image in the eye with lower retinal illuminance or contrast is processed more slowly than the image in the other eye [13][14][15][16][17][18][19] . The mismatch in processing speed causes a neural binocular disparity, a difference in the effective retinal locations of target images in the two eyes 20,21 , which results in the illusory motion in depth.The Pulfrich effect has been researched extensively since its discovery.…”