May 2008
Volume 8, Issue 6
Free
Vision Sciences Society Annual Meeting Abstract  |   May 2008
Attentional capacity is limited by the functional architecture of visual cortex: competition for representation impedes attention to multiple items
Author Affiliations
  • Pige Scalf
    Beckman Institute, University of Illinois at Urbana Champaign
  • Diane Beck
    Beckman Institute, University of Illinois at Urbana Champaign, and Department of Psychology, University of Illinois at Urbana Champaign
Journal of Vision May 2008, Vol.8, 221. doi:10.1167/8.6.221
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      Pige Scalf, Diane Beck; Attentional capacity is limited by the functional architecture of visual cortex: competition for representation impedes attention to multiple items. Journal of Vision 2008;8(6):221. doi: 10.1167/8.6.221.

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Abstract

We investigated whether competition among stimuli for representation in visual cortex may explain, in part, attention's limited capacity to act on multiple items. When multiple neighboring visual stimuli appear simultaneously, their representations interact in a mutually suppressive manner. Focusing attention on one of these stimuli reduces these suppressive effects, suggesting that attention may bias the competition for representation in favor of the attended item. If attention is divided among nearby stimuli, however, then once again, multiple, now attended, stimuli should be competing for representation. According to the theory, then, three attended items should be more vulnerable to competition than is one attended item. In two fMRI experiments, we presented participants with five complex visual stimuli. We manipulated whether attention was focused or divided by asking participants to detect the target in either one or three of the five locations. In Experiment 1, we manipulated the degree of inter-item competition by presenting items either sequentially or simultaneously. Competition could take place only among simultaneously presented stimuli. We assessed activation in V4 in each condition, and found an interaction between attentional and presentation conditions. Activation was significantly reduced during the attend-three condition relative to the attend-one condition, but only during simultaneous presentation. In Experiment 2, we manipulated the degree of inter-item competition by placing all three attended items within a single visual quadrant or by dividing them between the hemifields. Because representations in V4 are confined to contralateral space, only items presented within a single hemifield should compete. Preliminary data indicate that activation is less for the attend-three condition than the attend-one condition only when all attended items fall within a single hemifield. Together, these data indicate that attention is indeed less able to modulate competition when it must be divided among multiple items.

Scalf, P. Beck, D. (2008). Attentional capacity is limited by the functional architecture of visual cortex: competition for representation impedes attention to multiple items [Abstract]. Journal of Vision, 8(6):221, 221a, http://journalofvision.org/8/6/221/, doi:10.1167/8.6.221. [CrossRef]
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