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John Clevenger, Diane Beck; Refining The Resource Model: Cortical Competition Could Explain Hemifield Independence. Journal of Vision 2015;15(12):16. doi: 10.1167/15.12.16.
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© ARVO (1962-2015); The Authors (2016-present)
Recent studies have shown performance advantages in visual tasks when task-relevant stimuli are presented in different visual hemifields as opposed to a single hemifield. One way to interpret these findings is to posit that each cortical hemisphere has independent attentional resources. In contrast to this view, we suggest that competition between representations in visual cortex might explain this hemifield independence. When stimuli fall into separate hemifields, they project to different cortical hemispheres, reducing the local competitive interactions that occur when stimuli are presented in adjacent areas of a single hemisphere. To test whether local competitive interactions underlie hemifield independence, we had subjects search displays in which the target was placed such that it either shared a hemifield with non-targets or was alone in the hemifield. Set size was constant across all conditions. Critically, we also varied the overall display density (distance between objects). The resource account predicts the task should be harder when the target shares a hemifield with non-targets but predicts no difference when density is manipulated. Alternatively, the competition account predicts that sharing a hemifield should only make the task harder if the objects are close enough to strongly compete with one another (suppressing each others’ representations). We found that subjects were faster to find a target when the target was alone in the hemifield than when it shared the hemifield with non-targets, but only when overall display density was high (when the target was cortically near non-targets). These data suggest that hemifield independence might be caused by a lessening of local competitive interactions in visual cortex. When stimuli are cortically distant, either by being placed in separate hemifields or by being spread out, they are less likely to suppress each other’s representations in visual cortex and are thus easier to detect.
Meeting abstract presented at VSS 2015
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