Abstract
When dissimilar images are presented one to each eye, we do not see both images; rather, we see one at a time, alternating unpredictably. This is called binocular rivalry, and it has recently been used to study brain processes that correlate with visual consciousness, because perception changes without any change in the sensory input. Such studies have used various types of images, but the most popular have been gratings: sets of bright and dark lines of orthogonal orientations presented one to each eye. We studied whether using cardinal rival gratings (vertical, 0°, and horizontal, 90°) versus oblique rival gratings (left-oblique, –45°, and right-oblique, 45°) influences early neural correlates of visual consciousness, because of the oblique effect: the tendency for visual performance to be greater for cardinal gratings than for oblique gratings. Participants viewed rival gratings and pressed keys indicating which of the two gratings they perceived, was dominant. Next, we changed one of the gratings to match the grating shown to the other eye, yielding binocular fusion. Participants perceived the rivalry-to-fusion change to the dominant grating and not to the other, suppressed grating. Using event-related potentials (ERPs), we found neural correlates of visual consciousness at the P1 for both sets of gratings, as well as at the P1-N1 for oblique gratings, and we found a neural correlate of the oblique effect at the N1, but only for perceived changes. These results show that the P1 is the earliest neural activity associated with visual consciousness and that visual consciousness might be necessary to elicit the oblique effect.
Highlights
One part of the neuroscience of consciousness is the quest to identify neural processes that correlate with phenomenal consciousness [1]
Mean (SD) binocular rivalry dominance duration was 2.02 (0.67) seconds for cardinal gratings and 1.95 (0.65) seconds for oblique gratings; according to a one-way ANOVA on log-transformed data, these times were not significantly different, F(1, 14) = 2.12, p = .168, ηp2 = .13. This result suggests that our rival gratings produced the hallmarks of binocular rivalry—exclusivity, inevitability, and randomness [2,4,6] —and that our participants’ experiences of binocular rivalry did not differ between cardinal and oblique gratings, meaning that we did not find any evidence for the oblique effect
We set out to determine whether the results of Kaernbach et al [40] apply to experiments that use cardinal gratings, and to determine whether the oblique effect influences early neural correlates of visual consciousness
Summary
One part of the neuroscience of consciousness is the quest to identify neural processes that correlate with phenomenal consciousness [1]. Takacs et al [91] found that infrequent and unpredictable changes in the orientation of task-irrelevant gratings elicited a bigger visual mismatch negativity (vMMN), an ERP component thought to index preattentive visual change detection [92,93,94], from cardinal gratings than from oblique gratings. They concluded that the oblique effect does not require attention. We used an ERP paradigm similar to that of Kaernbach et al [40], and we compared ERPs from cardinal gratings with ERPs from oblique gratings, and ERPs from perceived changes with ERPs from not-perceived changes
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