Other recent work focuses on understanding how the visual system decomposes images into distinct surfaces along extracted edges, or decomposes image regions into multiple layers when viewing objects through transparent or semi-transparent media. In addition to this segmentation problem there is a corresponding problem of integration or interpolation that occurs when the occluding and/or the occluded surface is incompletely specified. This is often the case in natural cluttered scenes where object contours can be fragmented because of noise or occlusion by another object. Our understanding of how these disconnected elements are organised into percepts of unitary objects is still relatively incomplete, although in recent years interest in completion phenomena has escalated along with efforts to understand the mechanisms underlying contour and surface interpolation. In this project I have been investigating the grouping of segments in configurations containing illusory, partially closed and occluded contours, with special emphasis on the role of the contrast polarity of the elements to be grouped. The effect of contrast polarity has featured prominently in investigations of perceptual grouping and, in this research, I revisit and challenge some widely held assumptions on the sensitivity of a particular grouping process to variations in the contrast polarity of the elements to be grouped. My results indicate that the effect of contrast polarity reversals on the perception of occluded, occluding, and partially closed surfaces depends crucially on the spatial distribution of such reversals within the inducing configurations. These results suggest the previously unsuspected importance of image properties related to ecologically relevant constraints in the perception of illusory contours and occlusion.
Spehar B 2002 "The role of contrast polarity in perceptual closure" Vision Research 42 343-50 PDF
Spehar B Gillam B 2002 "Modal completion in the poggendorff illusion: support for the depth-processing theory" Psychological Science 13 306-12 PDF
Spehar B 2000 "Degraded illusory contour formation with non-uniform inducers in Kanizsa configurations: the role of contrast polarity" Vision Research 40 2653-9 PDF
ARC Small Grant Scheme in 1999 and 2000.
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