How does the brain decide in a visual scene which item is the figure and which are part of the ground? This perceptual decision can be based on many cues, all of which are of a probabilistic nature. For instance, size helps us distinguish between the figure and the ground, since smaller regions are often (but not always) figures. Object shape can help us distinguish figure from ground, because figures tend to be convex. Movement also helps; the figure may be moving against a static environment. Color is also a cue, because the background tends to continue as one color behind potentially multiple foreground figures, whose colors may vary. Edge assignment also helps; if the edge belongs to the figure, it defines the shape while the background exists behind the shape. But it's at times difficult to distinguish between the two because the edge that would separate figure from ground is really part of neither, it equally defines both the figure and the background.[6]
Evidently, the process of distinguishing figure from ground (sometimes called figure–ground segmentation) is inherently probabilistic, and the best that the brain can do is to take all relevant cues into account in order to generate a probabilistic best-guess. In this light, Bayesian figure–ground segmentation models have been proposed to simulate the probabilistic inference by which the brain may distinguish figure from ground.[7]