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Laura Cacciamani, Paige E. Scalf, Mary A. Peterson; Competition-based ground suppression in extrastriate cortex and the role of attention. Journal of Vision 2014;14(10):45. doi: https://doi.org/10.1167/14.10.45.
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© ARVO (1962-2015); The Authors (2016-present)
Theories of object perception posit that regions sharing a border compete for object status. The winner is perceived as the object, the loser as a shapeless ground. Previous research showed that neural representations of the ground are suppressed. Experiment 1 used fMRI to search for evidence that the amount of ground suppression varies with the amount of competition. Participants performed an RSVP task at fixation while task-irrelevant, novel silhouettes appeared in the upper left (LVF) or right visual field (RVF). Unbeknownst to participants, the silhouettes differed in whether well-known or novel objects were suggested on the groundsides of their borders (high- and low-competition silhouettes, respectively). We expect more suppression on the groundsides of the former than the latter. Results showed significantly less activation on the groundsides of high- vs. low-competition silhouettes in V4 and V2 (p<.05), which we interpret as greater ground suppression under conditions of greater competition. This effect was only observed for RVF/left hemisphere (LH) presentation. One explanation of this laterality effect is that more attention is captured by RVF than LVF stimuli. Experiment 2 tested this hypothesis by assessing whether conflict stimuli in the RVF draw more attention away from the RSVP task. A high- or low-competition silhouette appeared (RVF or LVF) on each trial while participants performed an RSVP task at fixation. RSVP performance was reduced when high- vs. low-competition silhouettes appeared in the RVF but not in the LVF (p<.05), suggesting that attention is indeed captured more by stimuli in the RVF than LVF. Experiment 1 provides neural evidence for competition-based ground suppression. Given our large displays (4o high), the V2 suppression is likely mediated by feedback from higher levels with larger receptive fields. Experiment 2 suggests that attention may be needed to resolve this competition. The precise role of attention remains to be elucidated.
Meeting abstract presented at VSS 2014
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