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. 2022 Nov 1;22(12):7.
doi: 10.1167/jov.22.12.7.

The effect of spatial structure on binocular contrast perception

Minqi Wang  1   2 , Jian Ding  1   3   4 , Dennis M Levi  1   3   5 , Emily A Cooper  1   3   6
Affiliations

The effect of spatial structure on binocular contrast perception

Minqi Wang et al. J Vis. .

Abstract

To obtain a single percept of the world, the visual system must combine inputs from the two eyes. Understanding the principles that govern this binocular combination process has important real-world clinical and technological applications. However, most research examining binocular combination has relied on relatively simple visual stimuli and it is unclear how well the findings apply to real-world scenarios. For example, it is well-known that, when the two eyes view sine wave gratings with differing contrast (dichoptic stimuli), the binocular percept often matches the higher contrast grating. Does this winner-take-all property of binocular contrast combination apply to more naturalistic imagery, which include broadband structure and spatially varying contrast? To better understand binocular combination during naturalistic viewing, we conducted psychophysical experiments characterizing binocular contrast perception for a range of visual stimuli. In two experiments, we measured the binocular contrast perception of dichoptic sine wave gratings and naturalistic stimuli, and asked how the contrast of the surrounding context affected percepts. Binocular contrast percepts were close to winner-take-all across many of the stimuli when the surrounding context was the average contrast of the two eyes. However, we found that changing the surrounding context modulated the binocular percept of some patterns and not others. We show evidence that this contextual effect may be due to the spatial orientation structure of the stimuli. These findings provide a step toward understanding binocular combination in the natural world and highlight the importance of considering the effect of the spatial interactions in complex stimuli.

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Figures

Figure 1.
Figure 1.
Top–down view of the haploscope used to present stimuli independently to the two eyes. The red line indicates the line of sight.
Figure 2.
Figure 2.
(A) Each image had a center-surround layout, in which the contrast of the center and surround could differ. (B) On each trial, two stimuli (four images) were shown. The dichoptic reference stimulus was fixed and had different contrasts between the two eyes except during catch trials. Participants increased or decreased the contrast of the central region of the nondichoptic adjustable stimulus to match the appearance of the reference stimulus. The surround contrast was always the same in both eyes and both stimuli.
Figure 3.
Figure 3.
A pair of dichoptic reference images shown to the left and right eye in the (A) mean surround condition (binocular edge), (B) low surround condition (monocular edge in the eye viewing higher contrast target), and (C) high surround condition (monocular edge around the lower contrast target).
Figure 4.
Figure 4.
Stimulus types used in experiment 1, each shown with center and surround both having contrast of 1. Stimuli included (A) sine wave gratings (1 cpd and 5 cpd), (B) natural textures (with amplitude spectra slopes of −0.9, −0.7, and −0.9 on a log–log scale (Olmos & Kingdom, 2004), and (C) 1/f noise. Three of the 1/f noise images were generated by phase scrambling the natural textures, the fourth (bottom right) was synthesized to have a slope of −1 in log-log space and a Gaussian intensity histogram.
Figure 5.
Figure 5.
Example images of the stimuli used in experiment 2, with center and surround both having contrast of 1. Stimulus types included (A) the vertical 5 cpd grating from experiment 1, (B) the 1/f noise pattern from experiment 1, (C) the noise pattern with histogram adjusted to match the grating, (D) the noise pattern with bandpass filtering centered at 5 cpd, and (E) a broadband grating.
Figure 6.
Figure 6.
Example images of high surround stimuli (surround contrast = 1) for the low contrast center eye (center contrast = 0.5) used in experiment 2. (A, B) The original 5-cpd grating and edge-blurred 5-cpd grating. (C, D) The original noise and edge-blurred noise.
Figure 7.
Figure 7.
Hypothetical data showing three different naive predictions about the perceived contrast of the reference stimulus. The grey color of each square corresponds to the matched adjustable stimulus’ contrast for a given left (x axis) and right eye contrast (y axis) of the reference stimulus. The patterns shown are: (A) adjustable stimulus matches the higher contrast reference image, (B) adjustable stimulus matches the average contrast of the two reference images, and (C) adjustable stimulus matches the lower contrast reference image.
Figure 8.
Figure 8.
Experiment 1 (N = 10), mean surround condition data averaged across all participants for the different stimulus types: (A, B) gratings, (C) noise stimuli, and (D) natural textures.
Figure 9.
Figure 9.
Experiment 1 results (N = 10) for the four stimulus types in the (A) mean surround, (B) low surround, and (C) high surround conditions. The box-and-whisker plots show the median weight of the higher contrast image across individuals, the 25th and 75th percentiles, and the nonoutlier range. The black dots indicate each participant's weight. The gray dash lines represent the weights for the three types of combination rules winner-take-all (1), averaging (0.5), and loser-take-all (0).
Figure 10.
Figure 10.
Experiment 2 results (N = 32) across the two surround conditions for the five stimulus types: the narrowband 5-cpd grating and noise baseline from experiment 1 (grating and noise), histogram-matched noise (hist eq), bandpass noise (bandpass), and broadband grating (broadband).
Figure 11.
Figure 11.
Additional stimuli tested in experiment 2. (A) Comparison between vertical (V) and horizontal (H) 5-cpd gratings. (B) The effect of edge blur on the vertical 5-cpd grating and noise. The red line indicates the line of sight.
Figure 12.
Figure 12.
Heatmaps showing the nondichoptic contrast match for all stimuli in the mean surround and high surround conditions for two observers in experiment 2. Subject A shows winner-take-all when the left eye sees the higher contrast, but not when the right eye sees the higher contrast in most situations. Subject B generally has the same response regardless of which eye saw higher contrast.
Figure 13.
Figure 13.
Comparison between trials where the dominant eye (top) or nondominant eye (bottom) was presented with the higher contrast image. Eye dominance is determined by 5cpd mean surround responses. (A) Experiment 1. (B) Experiment 2.
Figure 14.
Figure 14.
Cross-fusion examples of experiment 1 stimuli.
Figure 15.
Figure 15.
Cross-fusion examples of experiment 2 stimuli.
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