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Yongna Li, Neill W. Trammell; When two objects are easier than one: effects of object occlusion. Journal of Vision 2010;10(7):181. doi: 10.1167/10.7.181.
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According to theories of ""object-based attention"", it should be easier to divide attention between two attributes of one object, than between two attributes of two different objects.However, some studies find that two attributes can be compared faster when on separate objects than when on the same object (e.g., Burnham & Neill, 2006; Cepeda & Kramer, 1999; Davis & Holmes, 2005).This effect appears to occur when the whole objects can be compared more easily than component parts (Neill, Li & Seror, 2009).The present experiments investigate whether between-object superiority (BOS) can occur for partially obscured objects, via amodal completion. In the first experiment, subjects judged small notches in the ends of one or two rectangular ""objects"" as same or different in shape (rectangular and/or triangular). The spatial separation between the notches was equal for within- and between-object presentations.A third perpendicular object appeared to partially occlude either (a) both target objects, (b) only one target object, or (c) neither target object.Reaction times showed BOS if neither object was occluded, and also a smaller but significant effect when only one object was occluded.Surprisingly, there was no within- vs. between-object difference when both objects were partially occluded.The results suggest that BOS can occur for partially occluded objects, but amodal completion may only occur for an occluded object if cued by a non-occluded object.Follow-up experiments investigate the effects of intra-list and intra-trial cueing of amodal completion on between-object superiority.Implications for theories of object-based attention will be discussed.
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