Article

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: 3.43). 02/2009; 5(2):270-3. DOI: 10.1098/rsbl.2008.0622
Source: PubMed

ABSTRACT 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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    • "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.
    Journal of Vision 08/2010; 10(5):14. DOI:10.1167/10.5.14 · 2.73 Impact Factor
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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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