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Nour Malek, Julio Martinez-Trujillo; Binocular rivalry between spiral space stimuli in human observers: Expanding stimuli dominates over contraction and rotation. Journal of Vision 2011;11(11):309. doi: 10.1167/11.11.309.
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© ARVO (1962-2015); The Authors (2016-present)
During binocular rivalry, monocular stimuli compete for perceptual dominance. It is thought that rivalry arises from competitive interactions at different levels in the visual system between groups of neurons holding monocular representations of visual stimuli (Blake & Logothetis, 2002). It has been shown that increasing the strength of a visual representation by attending to it or increasing its contrast prolongs the corresponding rivalry period (Chong & Blake, 2002). We hypothesize that existing biases in the representation strength of expanding spiral stimuli in area MSTd shall prolong their corresponding rivalry periods (predominate) compared to other spiral motion types. In MSTd, expansion neurons outnumber contraction neurons by a ratio of ∼2:1, and rotation neurons by a ratio of ∼3:1 (Duffy & Wurtz, 1991; Graziano et al., 1994; Saito et al., 1986; Tanaka & Saito, 1989). We tested this hypothesis by measuring rivalry periods for combinations of expanding, contracting, and rotating random dot patterns (RDPs) in seven human observers. The RDPs were presented monocularly through a stereoscope and were matched for contrast and speed. We found that: a) expansion generally predominated over contraction (Wilcoxon Signed-Rank test, Left Eye (LE): p = 0.0156; Right Eye (RE): p = 0.0781), and rotation (LE: p = 0.02345; RE: p = 0.02345), b) contraction generally predominated over rotation although it did not reach statistical significance (LE: p = 0.1485; RE: p = 0.1953), and c) clockwise vs. counterclockwise rotations showed non-significant differences (LE: p = 0.8125; RE: p = 1.000). In a control experiment we measured rivalry periods for linearly moving RDPs in the four cardinal directions and found no differences in durations amongst these motion types. However, when comparing the rivalry periods between linear and complex motion types, periods were longer for spiral stimuli (p < 0.01). Our results suggest that biases in the representation of different spiral types by MSTd neurons can influence the competitive interactions underlying visual motion binocular rivalry.
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