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Woon Ju Park, Duje Tadin; Background subtraction as a mechanism for efficient motion segregation. Journal of Vision 2015;15(12):334. doi: https://doi.org/10.1167/15.12.334.
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© ARVO (1962-2015); The Authors (2016-present)
Segregation of objects from backgrounds is essential to everyday visual tasks. Computational and neurophysiological evidence suggests that segregation can be achieved by suppressing background motion signals. Behavioral evidence for this hypothesis, however, is lacking. Here, we hypothesized that spatial suppression (i.e., perceptual insensitivity to large, background motion; Tadin et al., 2003) enables rapid segregation of moving objects by suppressing motion signals belonging to the background, thereby effectively implementing background subtraction. Thus, efficient motion segregation should only occur for stimulus conditions linked with strong spatial suppression (e.g., high contrast stimuli and fast motion speeds). METHODS: We measured participants’ ability to segregate a small moving object (0.75° radius) presented on a large background (12° radius) that was either moving or stationary. Participants reported the target object location in a 4-AFC task. Duration thresholds were measured for both low and high contrast stimuli (3% and 99%) across different speed levels (1-16°/sec). RESULTS: At high contrast, participants were substantially better at object segregation when the background was moving than when it was stationary. For fast speeds (≥8°/sec), this advantage persisted even after we corrected for differences in relative motion between the two conditions. For slower speeds (≤4°/sec), the results were equivalent for moving and stationary backgrounds when corrected for relative motion differences. These results indicate that the presence of a moving background can strongly facilitate motion segregation—especially for fast, high-contrast stimuli. At low contrast, on the contrary, the benefits of the moving background largely disappeared. When the data were corrected for relative motion differences, stationary backgrounds elicited significantly better performance. CONCLUSIONS: These findings reveal highly efficient background subtraction under stimulus conditions that support strong spatial suppression. Evidently, perceptual insensitivity to large, background-like moving stimuli effectively implements background subtraction, which, in turn, enhances the relative visibility of moving objects.
Meeting abstract presented at VSS 2015
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