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Joy J. Geng, Jon Driver; Competition between stimuli in opposite visual fields. Journal of Vision 2005;5(8):999. doi: 10.1167/5.8.999.
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© ARVO (1962-2015); The Authors (2016-present)
We investigated the effect of unilateral and bilateral displays on visual processing of a spatially lateralized target using fMRI. Stimuli consisted of a high contrast visual target appearing either alone or with a visually similar distractor in the opposite visual field. The location of the target was randomly assigned on each trial to either the left or right visual field. No spatial cue was available prior to the onset of the display, resulting in spatial uncertainty that precluded anticipatory attentional enhancement of visual areas associated with an expected target location. Target-side specific contrasts of the two display conditions produced symmetrical and focal activations in the superior occipital gyrus contralateral to the target; Visual stimuli in unilateral displays produced stronger activation in these occipital sites than the same stimuli in bilateral displays, suggesting that distractor competition reduced associated BOLD activation in sensory cortex. Moreover, within bilateral displays, activations associated with target and distractor stimuli displays did not differ significantly from each other. Consistent with the existing literature on attentional control structures, we also found extensive frontal and parietal activations associated with processing of bilateral compared to unilateral displays, particularly in left and right intraparietal sulcus (IPS). Additionally, activation in both of these IPS sites was more correlated with activation in the left middle frontal gyrus in the bilateral than the unilateral condition reinforcing the notion of a frontal-parietal network in selective attentional processing. Furthermore, within attentional control structures, the right angular gyrus showed a specific interaction pattern such that there was repetition suppression for spatially repeated targets in bilateral but not unilateral displays suggesting a special role in spatial selection.
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