Abstract
Objects tend to be convex rather than concave, but convexity is not a strong figural cue in two-dimensional displays unless (1) multiple convex regions alternate with multiple concave regions, and (2) the concave regions are the same color (Peterson & Salvagio, 2008). To explain these effects, we hypothesized that the interpretation of a single large surface pre-empts that of multiple same-color concave shapes. Consequently, the competition from concave shapes at individual borders is reduced, and convex shapes dominate. On this surface pre-emption hypothesis, separated same-color concave regions in multi-region figure-ground displays would be perceived as portions of a single surface whereas separated same-color convex regions in the same displays would not. To test this hypothesis, we adapted a cued target discrimination paradigm Albrecht, et al. (2008) had used with three-dimensional displays for use with our 2-D figure-ground displays. We examined whether object-based attention benefits—shorter reaction times to a target appearing within the same object as a pre-cue rather than in a different object – are obtained for two same-color concave regions separated by a convex region but not for two same-color convex regions separated by a concave region. Consistent with the surface pre-emption hypothesis, object-based attention benefits were obtained for targets shown on same-color concave regions flanking a convex region but not for targets shown on same-color convex regions flanking a concave region (p <.05). This finding was apparent in both accuracy and inverse efficiency measures, but not in reaction times. Thus, results showed that separated same-color concave regions were perceived as portions of a single object (surface) completing behind the convex regions, which were perceived as different objects (figures). In addition, this experiment reveals that a particular pattern of object-based attention benefits in a cued target discrimination task can provide an indirect measure of figure-ground perception.