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Chris L.E. Paffen, Ignace T.C. Hooge, Jeroen S. Benjamins, Hinze Hoogendoorn; Pop-out for interocular conflict. Journal of Vision 2008;8(6):1076. doi: 10.1167/8.6.1076.
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Wolfe and Franzel (1988) concluded that an element containing interocular conflict does not ‘pop out’ during visual search. Here we show that this absence of pop out was mainly due to the specific setup used in their experiments and that a target with interocular conflict does pop out during search.
Observers performed a search task on elements either containing interocular conflict (horizontal and vertical orientations) or not. Elements were placed in a circular arrangement centered around the fixation point. Two basic conditions were tested: (1) a conflict target among non-conflict distractors and (2) a non-conflict target among conflict distractors. For each condition we varied set size. A target was present on 50% of the trials. Observers pressed a button indicating that a target was present or absent.
Results The absence of ‘pop-out’ in the Wolfe and Franzel study (1988) was found while presenting left- and right-eye images in alternating sequence at 30 Hz using a shutter arrangement. Using mirrors, we show that ‘pop out’ of interocular conflict does occur when the images are presented simultaneously. Search was faster for a conflict target among non-conflict distractors than for a non-conflict target among conflict distractors. Moreover, search times increased with increasing set-size when searching for the non-conflict target (slope: 120 ms), but were constant when searching for the conflict target (slope: 15 ms). This search asymmetry was not evident when the same stimulus was fused and presented to both eyes without conflict, eliminating the possibility that a feature in the fused percept was responsible for pop-out. In addition, search times did not depend on the alternation rate of the individual (conflict) elements. We conclude that interocular conflict is a pop out feature during visual search.
Wolfe, J.M., & Franzel, S.L. (1988). Binocularity and visual search. Perception & Psychophysics, 44, 81-93.
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