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Serena J. Butcher, Patrick Cavanagh; Within-field advantage for detecting repetitions.. Journal of Vision 2004;4(8):450. doi: 10.1167/4.8.450.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Previous studies have found that a letter repetition (e.g. letter names, independently of case or font) is more rapidly detected when presented bilaterally (one letter in each visual field) than unilaterally (both in the same field). These results suggest that letter recognition may proceed independently in the left and right hemifields, but must proceed sequentially when both letters are in one field. We tested whether this advantage would be found when the repetition to be detected was based not on an identity match, but on a physical match. Methods: Subjects indicated if there was a repetition of any two of four presented items, one in each quadrant. The items were letters, squares, or disks. The letters varied in identity (always upper case), the squares varied in color, and the disks varied in size. A repetition was present on half the trials and was either unilateral (the two repeated items within one visual hemifield, right or left), or bilateral (one of the two repeated items in each field). A control experiment evaluated the contribution of horizontal and vertical repetition alignment, independently of visual field. Results: Contrary to previous results, subjects were significantly faster at detecting unilateral repetitions (92ms faster for letters, 58ms faster for colors and 30 ms faster for sizes, all significant at p< .05 or better). The control studies showed that horizontal vs. vertical alignment did not account for the effects. Conclusions: The effect found here is larger than and in the opposite direction to previous findings for detecting letter repetitions. In our experiment, the repeated items are physically identical, offering an opportunity for low-level grouping to signal the repetition. Our data suggest that grouping acts more efficiently within hemifields than across fields. Previous studies based on high-level identity matches would not be able to call on this grouping function and would have missed the within-field advantage.
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