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Mary K. L. Baldwin, Izabela Trolka, Amanda R. Carson, Andrew F. Rossi; The effect of perceived depth on object substitution masking. Journal of Vision 2006;6(6):296. doi: 10.1167/6.6.296.
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Object substitution masking (OSM) is a type of backward masking that occurs during visual search (Enns & Di Lollo, 1997). OSM requires attention to the mask, which persists after the search array has been extinguished. Di Lollo et al. (2000) proposed that OSM occurs when there is a conflict between a reentrant target signal and subsequent lower level representation of the mask, resulting in a perceptual substitution of the mask for the target. Implicit in this hypothesis is that OSM operates on object-level representations. In our study, we tested whether a difference in depth between the target and mask disambiguates their representations, thereby eliminating OSM. Subjects viewed an array containing 8 objects positioned equidistant from central fixation. The display was viewed through a stereoscope and the perceived depth of the target and/or mask was defined by disparity relative to the fixation plane. Subjects reported whether or not a triangle had been presented in the location cued by the mask. Masking was observed in all conditions in which the mask and target were presented at different depth planes. The magnitude of the masking effect was between 75–100% of that observed in conditions in which the mask and target shared the same depth plane. In addition, masking was robust regardless of whether the target was perceived as in front, or behind the mask. Our findings suggest that OSM may operate at the level of object representation prior to the integration of disparity information.
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