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Thomas Wallis, Derek Arnold; Staying Focussed: The function of suppression during binocular rivalry?. Journal of Vision 2007;7(9):62. doi: https://doi.org/10.1167/7.9.62.
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© ARVO (1962-2015); The Authors (2016-present)
A central issue in contemporary binocular rivalry literature concerns whether suppression is driven by selections of a particular stimulus or by information from a specific eye. We propose an alternative - that suppression is controlled by an independent process which facilitates visibility near the point of fixation. This predicts that suppression should be governed by cues signalling distance from fixation, even when suppression is unambiguously related to a particular stimulus rather than to a specific eye. To explore this possibility, we used two presentation styles: classical rivalry, in which different images were shown to either eye for a period of 30 seconds, and stimulus rivalry, in which images were flickered (20 Hz) and swapped between the eyes (2 Hz). During stimulus rivalry suppression is evidently related to stimulus selections as average periods of exclusive perceptual dominance exceed the durations for which images are shown to either eye. We manipulated image blur across trials, such that as one image became progressively blurred the other became better focussed. For both classical and stimulus rivalry, focused images were persistently experienced whereas relatively blurred images were suppressed. Alternating dominance, for approximately equal periods, tended only to occur when images were equally focussed (e.g. both focussed or both blurred). Our data showed a smooth transition from the near total suppression to the near complete perceptual dominance of an image as blur difference changed - suggesting that blur is influential even when there is little or no blur difference. Image blur was found to be a stronger suppression determinant than either luminance contrast or colour. Our findings suggest that optics can determine suppression selectivity, even during stimulus rivalry. This is consistent with our proposal that suppression, during binocular rivalry, is an evolutionary adaptation which facilitates visibility near the point of fixation.
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