Segmentation; Shape and Object Perception
For each edge in the visual input, the visual system determines whether or not it is a shape boundary, and if it is, where the shape lies with respect to the edge (on the left or right side with respect to a vertical edge, for example). The processes resulting in this decision are shape segmentation processes.
Traditionally, it has been believed that shape segmentation is based on low-level stimulus properties only and is (at least initially) immune to high-level properties such as past experience and attention. In contrast, we argue that shape segmentation entails interactions between both low-level stimulus cues and high-level factors such as attention and past experience with particular shapes/objects.
In a series of experiments, we have shown that edges are more likely to be seen as boundaries of regions that portray familiar shapes when the shapes (such as sea horses, lamps, etc.) are depicted in the orientation in which they are typically seen, rather than in some other orientation. These effects are not obtained if the parts of the familiar object are spatially rearranged (scrambled), indicating that these effects are not solely dependent on the parts. (For review, see Peterson and Skow-Grant, 2003).
Currently, we are trying to uncover the mechanisms of shape segmentation by testing predictions arising from competitive models (Peterson & Enns, 2005; Peterson & Lampignano, 2003; see also Kim & Peterson, VSS 2005). In particular, we are testing a framework proposed by Peterson et al. (2000) that entails competition between, and mutual suppression of, shape properties on opposite sides of an edge (Peterson, et al., 2000; Peterson and Kim, 2001; Peterson and Skow, submitted). We are searching for evidence of this competition and suppression in both behavioral and brain imaging experiments.
Where is the shaped entity? You are likely to see the black region as the shaped entity first. But can you see the white region as such? We can measure competition from past experience with seahorse shapes even when the black region is consciously perceived to be the shaped entity.
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· segmentation; shape and object perception
· interactions between depth cues and shape cues
· grouping