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Duje Tadin, Chris L. E. Paffen, Frans A. J. Verstraten, Randolph Blake, Joseph S. Lappin; Perceived 3D surface layout modulates center-surround interactions in motion. Journal of Vision 2004;4(8):107. doi: 10.1167/4.8.107.
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Increasing the size of high-contrast moving patterns reduces both direction discrimination and motion aftereffect (MAE). Tadin et al. (2003, Nature, 424: 312) suggested that this counterintuitive effect results from surround suppression, perhaps in area MT. Surround suppression might occur because vision tends to suppress motion signals arising from background motion. We explored this hypothesis by examining how surround suppression is affected by figure/ground manipulations that alter the perceived visual extent of motion. We measured MAE strength following adaptation to a high-contrast, center-surround pattern. Consistent with our prior finding, adapting to the center alone yielded a stronger MAE than did adapting to the center and surround. But when the surround was stereoscopically presented at a different depth plane (either in front or behind the center), MAE strength increased. This finding accords with MT data indicating that surround suppression diminishes when center and surround regions are stimulated by motions at different disparities (Bradley & Andersen, 1998, J Neurosci, 18: 7552). In a second study, we used occlusion to change figure/ground appearance. The occluder (a Celtic cross with a central hole) was stereoscopically placed either in front of or behind a large moving grating. With the occluder behind, the grating was perceived as five detached small objects. This condition yielded a strong MAE. With the occluder in front, the same grating was perceived as a large object moving behind the occluder. This condition yielded a weak MAE. Our results show that surround suppression of motion signals is affected by cues other than motion. Evidently, suppression occurs when the visual context suggests a large moving surface. If the context suggests multiple moving surfaces, suppression is greatly reduced (even when local motion signals stay unchanged). This property highlights a possible functional role of surround suppression in figure-ground segregation.
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