More superimposition for contrast-modulated than luminance-modulated stimuli during binocular rivalry

Abstract

Luminance-modulated noise (LM) and contrast-modulated noise (CM) gratings were presented with interocularly correlated, uncorrelated and anti-correlated binary noise to investigate their contributions to mixed percepts, specifically piecemeal and superimposition, during binocular rivalry. Stimuli were sine-wave gratings of 2 c/deg presented within 2 deg circular apertures. The LM stimulus contrast was 0.1 and the CM stimulus modulation depth was 1.0, equating to approximately 5 and 7 times detection threshold, respectively. Twelve 45 s trials, per noise configuration, were carried out. Fifteen participants with normal vision indicated via button presses whether an exclusive, piecemeal or superimposed percept was seen. For all noise conditions LM stimuli generated more exclusive visibility, and lower proportions of superimposition. CM stimuli led to greater proportions and longer periods of superimposition. For both stimulus types, correlated interocular noise generated more superimposition than did anti- or uncorrelated interocular noise. No significant effect of stimulus type (LM vs CM) or noise configuration (correlated, uncorrelated, anti-correlated) on piecemeal perception was found. Exclusive visibility was greater in proportion, and perceptual changes more numerous, during binocular rivalry for CM stimuli when interocular noise was not correlated. This suggests that mutual inhibition, initiated by non-correlated noise CM gratings, occurs between neurons processing luminance noise (first-order component), as well as those processing gratings (second-order component). Therefore, first- and second-order components can contribute to overall binocular rivalry responses. We suggest the addition of a new well to the current energy landscape model for binocular rivalry that takes superimposition into account.

Temporary monocular occlusion facilitates binocular fusion during rivalry

“…We designed Experiment 2 to assess this idea. We adapted a rivalry task previously developed by Skerswetat et al (2017) to investigate patching-induced changes in the relative predominance of superimposition and piecemeal mixed percepts. Whereas superimposition per-cepts can be thought of as fully fused binocular percepts, the result of weakened interocular suppression, piecemeal percepts can be considered to be intermediary binocular percepts, in which rivalry is still occurring in smaller subregions (Alais & Melcher, 2007;Klink et al, 2010;Kovacs et al, 1996;Lee & Blake, 2004).…”

“…We designed Experiment 2 to investigate whether short-term monocular patching preferentially affects superimposition versus piecemeal mixed percepts during binocular rivalry. This experiment used a 4AFC binocular rivalry task adapted from Skerswetat et al (2017) to evaluate patching-induced changes in rivalry dynamics.…”

“…We adapted a 4AFC binocular rivalry task used by Skerswetat et al (2017; Figure 1D) to quantify the overall fraction of exclusive, piecemeal, and superimposition mixed percepts. At the beginning of each session, participants were shown images on a document that illustrated the differences between the left-oriented, right-oriented, and superimposition versus piecemeal mixed percepts.…”

“…Although binocular rivalry is often characterized as a series of perceptual alternations between two competing images, the actual visual experience is more extensive and can be separated into three categories: (a) exclusive visibility, when one eye's signal is entirely suppressed by the other eye's image; (b) piecemeal mixed visibility in which information from both eyes is simultaneously visible in smaller spatially segregated areas, sometimes described as local rivalry (Skerswetat, Formankiewicz, & Waugh, 2017); and (c) superimposition mixed visibility in which information from both eyes is visible and combined to constitute a fused binocular percept (Brascamp, van Ee, Noest, Jacobs, & van den Berg, 2006;Liu, Tyler, & Schor, 1992). Importantly, mixed visibility highlights instances when complete interocular suppression fails, allowing binocular combination to occur.…”

“…Experiment 2 was a follow up to Experiment 1 to determine whether piecemeal or superimposition percepts were specifically targeted by the effects of deprivation. To investigate this, we used a task adapted from Skerswetat et al (2017) that allowed us to simultaneously measure patching-induced changes in perceptual eye dominance as well as the relative predominance of superimposition and piecemeal percepts.…”