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Wesley Kinerk, Michael Martorana, Erwin Wong; Dichoptic Collinear Lateral Masking at Long Stimulus Onset Asynchronies Produces Surprising Suppression of Contrast Detection. Journal of Vision 2012;12(9):99. doi: https://doi.org/10.1167/12.9.99.
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© ARVO (1962-2015); The Authors (2016-present)
At VSS 2010 we reported the results of a pilot study that investigated the effect of varying interstimulus interval (ISI) and flank duration on contrast detection threshold (CDT) of a sinusoid target under monoptic and dichoptic viewing. We now report on the completed study including half-binocular viewing, longer stimulus onset asynchronies (SOA), and a supplemental experiment using orthogonal flanks. 11 observers with normal vision participated for a mean of 25 hours each. In the main experiment, target and flanks were 3 cpd vertical sinusoids with 6 lambda (sigma = 1.5 lambda) center-to-center vertical separation. Flank contrast was normalized to 3X flank CDT. Flanks were presented at 4 durations (67-500ms) and ISIs at 7 durations (0-2500ms) resulting in SOAs from 0-3000ms. Target presentations were 250ms to the dominant eye via mirror haploscope and septum. Flanks were presented to dominant (monoptic and half-binocular) and non-dominant eyes (dichoptic and half-binocular). Forward masking was used with a 1-FC detection paradigm and 7-level MOCS. Each threshold was calculated from approximately 700 trials. As expected, simultaneous presentation resulted in CDT facilitation (monoptic = 18.9±3.86% (SE), dichoptic = 13.9±4.00%, half-binocular = 18.0±4.20%). For all viewing conditions, relative facilitation decreased as SOA increased up to 1000ms. Surprisingly, dichoptic and half-binocular viewing showed CDT suppression at long SOAs beginning at 400-500ms, with maximal suppression (9.9±5.1% and 5.3±4.7%, respectively) occurring at 1000ms. All viewing conditions approached no effect at the longest SOAs (1500-3000ms). Flank duration had a significantly greater contribution to the overall effect than ISI for dichoptic and half-binocular viewing. We found no significant difference in contribution under dichoptic viewing. Dichoptic, orthogonal flanks did not produce CDT suppression. We speculate that the CDT suppression observed at long SOAs under dichoptic and half-binocular viewing is due to one-way, contrast adaptation from lateral propagation that produced the effect of a collinear, illusory contour.
Meeting abstract presented at VSS 2012
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