1 Introduction
The Gestalt laws of perception have long recognized figural closure as one of the primary perceptual phenomena exploited by the human visual system. The detection of closure is fast, automatic, and seemingly effortless, and its role in building intermediate level descriptions is well-recognized [5], [7], [8], [10], [13]. The conventional explanation for why a visual system should seek closed or nearly closed contours is that coherent objects tend to be spatially compact and relatively uniform in surface appearance with respect to the surrounding background. Closure is thus viewed as a key cue for figure/ground segmentation. Abstracting away from cues about interior and exterior region properties, the typical psychophysical demonstration of figural closure employs straight or curved lines defining a region's bounding contour.