Very few exclusive percepts for contrast-modulated stimuli during binocular rivalry

Abstract

Binocular rivalry properties for contrast-modulated (CM) gratings were examined to gain insight into their locus of processing. Two orthogonally orientated gratings were presented, one to each eye. Perceptual change rates, proportions of exclusivity and mixed percepts, and mean durations were calculated. Stimuli were noiseless luminance-defined (L), luminance-modulated noise (LM) and contrast-modulated noise (CM) gratings with sizes of 1, 2 and 4deg and spatial frequencies of 4, 2 and 1c/deg, respectively. For the LM and CM gratings, binary noise was fully correlated between eyes. Maximum producible modulations were used (1.0 for CM, 0.78 for LM and 0.98 for L stimuli). In a control experiment, contrasts of LM gratings were reduced until the multiples over detection threshold were similar to those of CM stimuli. Trial durations of 120s were analyzed. Exclusive visibility decreased with increasing stimulus size regardless of the stimulus type. Even with visibilities at similar multiples above detection threshold, significantly lower proportions of exclusive percepts and perceptual changes were found for CM, compared to LM gratings. The results obtained with dichoptically presented orthogonal CM gratings are significantly different from those obtained for orthogonal gratings presented to one eye. CM stimuli therefore do engage in binocular rivalry but with different characteristics to those found for LM stimuli. These results suggest that CM stimuli are processed by a mechanism that promotes binocular combination rather than rivalry, and therefore may involve cells in a higher visual area than those that initially process LM information.

The effect of stimulus strength on binocular rivalry rate in healthy individuals: Implications for genetic, clinical and individual differences studies

“…Returning to MPD, the results also show that increasing the aperture size of an 8 cycles/s stimulus from 1°to 1.5°significantly reduced the total MPD in a given observation period, with MPD not differing significantly between 4 and 8 cycles/s stimuli in a 1.5°aperture. This finding is in contrast to reports that increasing stimulus aperture size decreases exclusive visibility (i.e., increases MPD; [8,63,78]). However, the stimuli assessed in the current study subtended 0.5°, 1°and 1.5°, thus varying across a much narrower range than that in [63]; i.e., stimuli subtended between 0.5°and 8°).…”

“…With respect to all stimulus parameters, it remains possible that additional modulation of BR rate (and MPD) might become evident if a wider range of such parameters (e.g., spatial frequency) and a wider range of values within each parameter (e.g., drift speeds, aperture sizes) were tested than those in the current study. Further work with multiple stimulus parameter combinations and variations could clarify their effect on BR temporal dynamics (e.g., [78]). The implications of the current BR rate findings for future endophenoptype studies are discussed further below.…”

“…As such, reducing an individual's total MPD provides more data on which to base the calculation of BR rate and thus improves accuracy of the BR rate measure. There have been reports that smaller BR stimuli between 0.5°and 2°of visual angle increase exclusive percept visibility ( [63]; see also [8,78]), which corresponds to a shorter MPD. The current study thus aimed to examine whether reducing the size of a BR stimulus from 1.5° [53,54] to 1°or 0.5°of visual angle would produce a shorter MPD.…”

“…We did not assess stimuli subtending larger than 1.5°so as to avoid inducing a longer MPD. Furthermore, because earlier studies examining the effect of stimulus size on exclusive visibility used only small samples ( [8,64,78]; n = 3 and 4 and 11, respectively), the current study employed a comparatively large dataset (n = 40) to clarify the effect of stimulus size modulation on MPD. However, interpretation of these MPD data will require caution as the mixed-percept response option also included subjects' erroneous responses (see Methods and Discussion).…”

Interocular suppression patterns in binocularly abnormal observers using luminance- and contrast-modulated noise stimuli

“…In addition to luminance and motion stimuli, the visual system is also sensitive to second-order spatial characteristics, such as modulations of contrast (contrast-modulated or CM stimuli) or texture, without a change in mean luminance. These second-order targets require extra stages of processing to be extracted by the visual system above that required for first-order luminance targets, which may occur in cortical units receiving predominantly binocular input (Wong, Levi, & McGraw, 2001Hairol & Waugh, 2010;Chima et al, 2015;Skerswetat, Formankiewicz, & Waugh, 2016). In amblyopia and strabismus, reduced sensitivity to CM stimuli above that found in normal eyes may be expected due to binocular disruption.…”