The movement of motion-defined contours can bias perceived position

Department of Psychology, Royal Holloway, University of London, Egham TW20 0EX, UK.
Biology letters (Impact Factor: 3.25). 02/2009; 5(2):270-3. DOI: 10.1098/rsbl.2008.0622
Source: PubMed


Illusory position shifts induced by motion suggest that motion processing can interfere with perceived position. This may be because accurate position representation is lost during successive visual processing steps. We found that complex motion patterns, which can only be extracted at a global level by pooling and segmenting local motion signals and integrating over time, can influence perceived position. We used motion-defined Gabor patterns containing motion-defined boundaries, which themselves moved over time. This 'motion-defined motion' induced position biases of up to 0.5 degrees , much larger than has been found with luminance-defined motion. The size of the shift correlated with how detectable the motion-defined motion direction was, suggesting that the amount of bias increased with the magnitude of this complex directional signal. However, positional shifts did occur even when participants were not aware of the direction of the motion-defined motion. The size of the perceptual position shift was greatly reduced when the position judgement was made relative to the location of a static luminance-defined square, but not eliminated. These results suggest that motion-induced position shifts are a result of general mechanisms matching dynamic object properties with spatial location.

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Available from: Szonya Durant
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    • "Further evidence points to the role of MT/V5 in the etiology of the motion signal that modulates perceived position in both motion-induced position shifts and motion drag. Motion-defined contours that can only be seen at a global level, by pooling and segregating local motion signals and integrating over time, also appear shifted in position (Durant & Zanker, 2009). Position shifts in luminance modulated drifting random dot fields increase with motion coherence (Mussap & Prins, 2002). "
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    ABSTRACT: The perceived position of stationary objects can appear shifted in space due to the presence of motion in another part of the visual field (motion drag). We investigated this phenomenon with global motion Gabor arrays. These arrays consist of randomly oriented Gabors (Gaussian windowed sinusoidal luminance modulations) whose speed is set such that the normal component of the individual Gabor's motion is consistent with a single 2D global velocity. Global motion arrays were shown to alter the perceived position of nearby stationary objects. The size of this shift was the same as that induced by arrays of Gabors uniformly oriented in the direction of global motion and drifting at the global motion speed. Both types of array were found to be robust to large changes in array density and exhibited the same time course of effect. The motion drag induced by the global motion arrays was consistent with the estimated 2D global velocity, rather than by the component of the local velocities in the global motion direction. This suggests that the motion signal that induces motion drag originates at or after a stage at which local motion signals have been integrated to produce a global motion estimate.
    Full-text · Article · Aug 2010 · Journal of Vision
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    • "This role for grouping processes is supported by evidence that the interpretation of bistable motion can alter perceived motion drag (Shim & Cavanagh, 2004). Position shifts are also found in second-order stimuli such as contrastdefined or motion-defined contours (Bressler & Whitney, 2006; Durant & Zanker, 2009) and global motion random dot displays (Mussap & Prins, 2002). In addition, Edwards and Badcock (2003) reported a perceptual shift in perceived depth for expanding and contracting motion fields consistent with the conclusion that the objects appear shifted in the direction of motion in 3D space. "
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    ABSTRACT: Objects in motion appear shifted in space. For global motion stimuli we can ask whether the shift depends on the local or global motion. We constructed arrays of randomly oriented Gaussian enveloped drifting sine gratings (dynamic Gabors) whose speed was set such that the normal component of motion was consistent with a single global velocity. The array appears shifted in space in the direction of the global motion. The size of the shift is the same as for arrays of uniformly oriented dynamic Gabors that are moving in the same direction at the same global speed. Arrays made up of vertically oriented gratings whose speeds were set to the horizontal component of the random array elements were shifted less far. This shows that motion-induced position shifts of coherently moving surface patches are generated after the completion of the global motion computation.
    Full-text · Article · Dec 2009 · Journal of Vision
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    ABSTRACT: The position of a visual pattern moving within a static aperture appears to be displaced in the direction of motion. This illusory position shift can be induced by luminance-defined as well as contrast-defined motion. The present study used a random-dot binocular correlogram in which a moving square-wave grating was solely defined by binocular correlations. This cyclopean motion was found to induce illusory position shift. Consistent with previous reports on position shift induced by second-order motion, the illusion was smaller than that found in the case of the first-order motion. This pattern of results unequivocally demonstrates the existence of a binocular mechanism mediating this illusion.
    Full-text · Article · Jun 2009 · Vision research
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