process of segregating a scene into objects is fundamental to visual
perception, but it is not yet understood. The traditional view holds that
convexity is a powerful predictor of where objects lie in a scene. This view
derives from the Gestalt theoretical perspective and was supported by
demonstrations with multi-region (n = 8 regions) displays. We systematically
varied the number of alternating convex and concave regions in a display from 2
to 8 and found that convexity is a weak object cue in 2 region displays. Convex
regions are increasingly likely to be perceived as objects as the number of
alternating convex and concave regions increases, provided that (a) the concave
regions are homogeneously colored and (b) the scene affords a 3D, rather than a
2D, interpretation. These "context effects" take time to emerge.
Symmetry also operates probabilistically and increases in effectiveness as an
object cue with increasing numbers of alternating symmetric and asymmetric
regions when the two conditions above are satisfied, although context effects
are weaker for symmetry.