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Matthew Hayes, Khena Swallow, Yuhong V. Jiang; Competitive interaction for visual representation between and within hemifields. Journal of Vision 2008;8(6):465. doi: 10.1167/8.6.465.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies have shown that when multiple objects are presented, performance is sometimes enhanced, and sometimes impaired, when the objects fall unilaterally within one visual hemifield rather than bilaterally in two hemifields. In detecting repetition of letters, for instance, a bilateral advantage is observed when the repeated letters are semantically identical but visually different (e.g., “A” and “a”), while a unilateral advantage is observed when repeated letters are visually identical (e.g., “A” and “A”). This study aims to elucidate conditions under which unilateral objects cooperate rather than compete for processing resources. We presented four items, one in each visual quadrant, and asked observers to judge whether all four objects were different, or whether two of them were the same along an instructed dimension. The “same” objects could fall in the same hemifield, in two separate hemifields, or in diagonal positions. They could be visually identical or different in features irrelevant to the task. Results showed that when detecting the repetition of objects, a unilateral advantage was observed even when the objects differed in size or viewing angle, suggesting that a unilateral advantage is not restricted to the detection of identical objects. The unilateral advantage, however, depends on the complexity of visual objects. It was observed with repetition detection of colors, letters, and simple objects, where simple distinctive features can be used to identify the repetition. No hemifield effects were observed when detecting the repetition of complex scenes and novel objects that lacked distinctive features, and a bilateral advantage was seen when detecting the repetition of faces. We conclude that objects within a hemifield cooperate in tasks that rely significantly on perceptual grouping (Butcher & Cavanagh, 2004 VSS) along a task-relevant visual dimension.
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