September 2015
Volume 15, Issue 12
Vision Sciences Society Annual Meeting Abstract  |   September 2015
Early, local motion signals generate directional preferences in depth ordering of transparent motion
Author Affiliations
  • Alexander Schütz
    Department of Psychology, Justus-Liebig-University Giessen, Germany
  • Pascal Mamassian
    CNRS & Ecole Normale Supérieure, Paris, France
Journal of Vision September 2015, Vol.15, 6. doi:
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      Alexander Schütz, Pascal Mamassian; Early, local motion signals generate directional preferences in depth ordering of transparent motion. Journal of Vision 2015;15(12):6.

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      © ARVO (1962-2015); The Authors (2016-present)

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Superposition of two dot clouds moving in different directions results in the perception of two transparent layers with ambiguous depth order. Intriguingly, the layer moving downwards or rightwards is preferentially seen in front (Mamassian & Wallace, 2010). Here we investigated which motion properties are causing these directional biases. In four experiments, we manipulated global properties of the dot clouds or local properties of individual dots to measure their influence on depth ordering. In all experiments, observers indicated the layer they saw in front. First, we found that the location in the visual field of the apertures within which the dots were presented did not affect depth ordering. This means that the directional biases were not related to the direction of optic flow induced by a translating observer (Gibson, 1950). Second, when the individual dots and the apertures were moving in different directions, only the motion direction of the dots determined the depth ordering. Third, when the moving elements were oriented lines rather than dots, the directional biases were strongly shifted towards the direction orthogonal to the lines rather than the motion direction of the lines. Perceived motion direction was also influenced by line orientation, but less so. This means that depth order was determined before the aperture problem was fully resolved (Pack & Born, 2001). Finally, varying the duration of the stimuli, we found that the time constant of the aperture problem was much lower for depth order than for perceived motion direction. Altogether, our results indicate that depth order is determined in one shot on the basis of an early motion signal, while perceived motion direction is continuously updated. Thus, depth ordering in transparent motion appears to be a surprisingly fast process, that relies on early, local motion signals (Qian et al., 1994) and that precedes high-level motion analysis.

Meeting abstract presented at VSS 2015


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