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David Somers, Summer Sheremata; Cross-hemifield attention benefits for visual enumeration. Journal of Vision 2008;8(6):983. doi: 10.1167/8.6.983.
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© ARVO (1962-2015); The Authors (2016-present)
Visual enumeration, the ability to determine the number of objects presented visually, has been shown to consist of a subitizing range (∼3 or fewer objects) and a counting or estimating range ([[gt]]∼3). Subitizing occurs rapidly, accurately with minimal attentional demands, while counting or estimating is slower, more prone to errors and strongly dependent on spatial attentional effects. The Zoom Lens theory of spatial attention (Erikson & St. James, 1986) predicts that performance in an attentionally demanding task should decline as the spatial extent of visual attention is broadened. However, recent evidence has suggested performance benefits from splitting the spotlight of attention and in deploying attention to both visual hemifields (e.g., Awh & Pashler, 2000; McMains & Somers, 2004; Alvarez & Cavanagh, 2005). Previously Green & Bavelier (2006) investigated the effects of increased spatial spread of targets on enumeration ability. Consistent with the Zoom Lens model, performance declined as spatial extent increased. Here we have re-investigated this issue, specifically investigating the influence of spreading targets across single or multiple visual hemifields and/or quadrants. Contrary to the predictions of the zoom lens model, enumeration performance was better when targets were placed in opposing quadrants in the right and left hemifields than when targets were restricted to a single quadrant. Performance in the “split quadrant” condition closely matched the predictions of a simple model of hemispheric independence that was derived from the single quadrant performance data. Performance was further enhanced when targets were distributed across all four visual quadrants. These results demonstrate that enumeration benefits from recruiting attentional resources in both hemifields. One possible explanation is that subitizing might occur in parallel across multiple attentional foci.
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