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Alexander C. Schütz; Interactions of depth order and numerosity in transparent motion. Journal of Vision 2012;12(9):151. doi: 10.1167/12.9.151.
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© ARVO (1962-2015); The Authors (2016-present)
In transparent motion the depth order of the two surfaces is ambiguous. However there are sustained biases to see certain directions in the back and others in the front (Mamassian & Wallace, Journal of Vision, 2010). Recently we showed that there are also biases to see the surface that contains more dots in the back (Schütz, Journal of Vision, in press). Here we investigated how motion direction, depth order and numerosity interact in transparent motion. We presented two overlapping random dot kinematograms (RDK) for one second within a circular aperture of 10 deg radius on a uniform gray background. The RDKs were moving along cardinal or oblique directions, with the two directions separated by 45 deg. The overall dot density was fixed at one dot/deg² and we manipulated the distribution of dots to the two RDKs in ratios from 0.2 to 0.8. In separate sessions observers were asked to indicate the direction of the surface containing more dots or the direction of the surface perceived in the back. We replicated the finding that the surface containing more dots tends to be seen in the back. Furthermore there were strong directional biases for numerosity judgments as well as for depth order judgments. These directional biases for numerosity and depth order judgments were highly correlated within observers. Thus directions that were more likely to be perceived in the back, were also more likely to be perceived as more numerous. These results indicate that there is either a bidirectional interaction of perceived depth order and perceived numerosity or that both perceptual aspects are influenced by a third, common factor. One such possibility would be that the visual system implicitly adjusts the perceived numerosity of the surface in the back, in order to compensate for the occlusion by the front surface.
Meeting abstract presented at VSS 2012
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