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Paige Scalf, Diane Beck; The effects of dividing attention on target enhancement and distractor inhibition. Journal of Vision 2011;11(11):104. doi: 10.1167/11.11.104.
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Visual attention is less effective at enhancing signal in extrastriate cortex when it is directed to multiple items rather a single item (McMains & Somers, 2005) and this limit is due in part to suppressive interactions in visual cortex (Scalf and Beck, 2010).
Attention also plays an important role in inhibiting extrastriate signal evoked by task-irrelevant distractor items (e.g. Pinsk et al., 2004). Consequently, the same extrastriate interactions that constrain the attentional enhancement of task-relevant material may also have consequences for the inhibition of task-irrelevant material. In the current experiment, we examine whether directing attention to multiple items rather than a single item alters the ability of attention to inhibit evoked extrastriate signal to task-irrelevant items. We also examine whether such an effect is dependent on the presence of suppressive interactions among attended items. Participants underwent high resolution (1.3 × 1.3 × 1.8 mm) EPI scanning. They viewed eight-element displays and covertly monitored these for a color/shape/texture conjunction. We manipulated the number of attended items by asking participants to alternate between attending to one or three locations. We manipulated the likelihood of suppressive interactions among attended items by shifting the location of the attended items from a midline position (at which items are projected to different hemispheres and thus are less likely to interact) to a position in the upper right visual field (at which items are projected to the same hemisphere and thus are subject to local suppressive interactions). Preliminary data from V2 indicate that both target enhancement and distractor inhibition are compromised when attention is directed towards multiple items, but only when those attended items are subject to local suppressive interactions.
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