Academic journal article Psychonomic Bulletin & Review

Grounding the Figure: Surface Attachment Influences Figure-Ground Organization

Academic journal article Psychonomic Bulletin & Review

Grounding the Figure: Surface Attachment Influences Figure-Ground Organization

Article excerpt

We investigated whether the lower region effect on figure-ground organization (Vecera, Vogel, & Woodman, 2002) would generalize to contextual depth planes in vertical orientations, as is predicted by a theoretical analysis based on the ecological statistics of edges arising from objects that are attached to surfaces of support. Observers viewed left/right ambiguous figure-ground displays that occluded middle sections of four types of contextual inducers: two types of attached, receding, vertical planes (walls) that used linear perspective and/or texture gradients to induce perceived depth and two types of similar trapezoidal control figures that used either uniform color or random texture to reduce or eliminate perceived depth. The results showed a reliable bias toward seeing as "figure" the side of the figure-ground display that was attached to the receding depth plane, but no such bias for the corresponding side in either of the control conditions. The results are interpreted as being consistent with the attachment hypothesis that the lower region cue to figure-ground organization results from ecological biases in edge interpretation that arise when objects are attached to supporting surfaces in the terrestrial gravitational field.

In optical projections of multiobject visual scenes, objects often partially occlude other objects, producing adjacent image regions that share a contour. To determine the shapes and relative distances of corresponding environmental objects, the visual system must determine which regions correspond to occluding foreground surfaces and which to occluded background surfaces. Figure-ground processes are assumed to be responsible for labeling regions as occluding figures or occluded grounds-in part, to determine which regions should be attended and recognized from the shape of the contour on that side.

Gestalt psychologists approached figure-ground organization by identifying perceptual cues that influence which region(s) are likely to appear as figure versus ground (for reviews, see Palmer, 1999, 2002). Rubin (1915/1958) first identified and studied several basic figural cues, such as the fact that a smaller region tends to be perceived as figure and a larger region as ground. Similarly, symmetric regions (Bahnsen, 1928), convex regions (Kanizsa & Gerbino, 1976), familiar regions (Peterson, 1994, 1999), and regions with wide bases (Hulleman & Humphreys, 2004) are more likely to be perceived as figure than are asymmetric, concave, unfamiliar, and narrow-based regions, respectively. Of most relevance to the present article, a region appearing below a common edge in the visual field is more likely to be perceived as figure than is a region appearing above this edge (Vecera, Vogel, & Woodman, 2002), as is illustrated in Figure 1A.

Although certain aspects of figure-ground cues are well understood, their origin is not. Some writers have suggested that perceptual organization processes might be innate (e.g., Koffka, 1935; Zuckerman & Rock, 1957), whereas others have argued that they are learned through experience with the visual environment (Ross-Sheehy, Oakes, & Vecera, 2003). In either case, environmental regularities are crucial, because statistical differences in the projected properties of closer versus farther objects are presumed to underlie the utility of such cues. Symmetric regions, for example, are more likely to be perceived as figures because symmetric regions in images are more likely due to the projection of a symmetric object (figure) than to two asymmetric objects accidentally creating a symmetric space between them (ground). Recent studies of the statistics of natural scenes document the ecological validity of certain locally defined figure-ground cues, including smaller size, convexity, and, of particular relevance to the present article, lower region (Fowlkes, Martin, &Malik, 2001).

One premise of the present research is that the statistical regularities of the environment that influence figure-ground organization are not restricted to intrinsic properties of individual objects. …

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