Abstract
Crowding is an inability to accurately perceive objects surrounded by visual clutter and is arguably the most fundamental limit on conscious object recognition throughout most of the visual field. The stage of visual processing at which crowding occurs is still debated. Previous research has shown crowding strength can be altered by pop-out effects. For example, crowding is decreased when binocular disparity is used to manipulate the perceived depth of targets and flankers [Felisbert et al, 2005]. Another possible depth cue is shape from shading, which produces not only a perception of depth, but also pop-out effects that reveal an inherent lighting from above assumption [Kleffner and Ramachandran, 1992]. To determine if crowding occurs after the inference of lighting direction, we tested whether pop-out caused by lighting interpretation reduces crowding. We presented oriented Gabors superimposed on shaded disks (e.g., shaded "bumps" or "dimples" with implied lighting from above). The central target Gabor was surrounded by a circular array of Gabor flankers superimposed on disks shaded in the opposite direction of the target disk. We also tested disks shaded from the side, as opposed to the top or bottom, which do not appear to have a strong depth difference. We found that target identification is improved in scenes consistent with a lighting from above interpretation, in which the target appears to differ from the flankers in depth (e.g., a "bump" among "dimples), when compared to scenes lit from the left or the right. This result is evidence that crowding of orientation occurs at a relatively late stage of processing, after lightness interpretations are completed.
Meeting abstract presented at VSS 2012