Rapid detection of salient regions: evidence from apparent motion.

Most studies that have used Kanizsa-type illusory figures to investigate perceptual completion have treated the crisp bounding illusory contours (ICs) and the enclosed region as nondissociable stimulus attributes. However, there is evidence that enclosed "salient regions" (SRs; Stanley & Rubin, 2003) are detected even in cases when bounding ICs are not perceptually completed. Here we used apparent motion (AM) to test whether SRs are detected in the absence of crisp bounding ICs. Kanizsa-type stimuli were modified in ways that eliminated the bounding ICs, but the clear impression of an enclosed region remained. SR stimuli were embedded in an array of like inducers. On successive frames, the inducers in the array rotated in a way that resulted in translation of the enclosed region. Four speeds of translation were tested. Observers performed a two-alternative forced-choice task on the direction of translation. Perceptually completed SRs produced robust AM whether they were bound by crisp ICs or not-observer performance was as good and, in certain cases, even better for SRs with no bounding ICs. We interpret these findings within a theoretical framework that makes a distinction between region-based and contour-based segmentation processes that operate in concert to achieve segmentation of the visual scene.