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要旨:
Recent theoretical work (Anderson, VSS 2001) has shown that occlusion geometry introduces an asymmetry in the depth relationships that can be inferred from near versus far contrast signals. Here, we show how this analysis predicts that the figure-ground relationships of a contour can be resolved by manipulating the depth of a few 3D dots.
Methods: We used two paradigms to assess the encoding of contours in ambiguous figure-ground displays. In Experiment 1, subjects were presented with a rectangle divided into light and dark halves by an irregular contour. Their task was to recall the shape of the dividing contour. A second screen contained either the left or the right half of the rectangle. Subjects indicated whether the irregular contour of the second shape was the same as in the first screen. Perceived border ownership in the 1st screen was manipulated with a few (2 or 6) dots; disparity either placed the dots behind, or in front of, the other half of the display. In Experiment 2 subjects observed similar displays and reported which side appeared as figure, and which as ground.
Results: When the dots were in front of the dividing contour, there was little effect on subjective judgments of figure-ground in Experiment 2, or the reaction times of Experiment 1. This implies that relatively near features (dots) do not uniquely specify the border ownership of further edges. However, when subjects were tested with the half that had contained dots more distant than the contour, reaction times were slowed. In this configuration, the far dots “capture” the regions surrounding the dots to a depth behind the contour, which resolves the border ownership of the contour.
Conclusions: There is an inherent asymmetry in the ability of relatively near and far depth signals to resolve border ownership. We will discuss how the failure to appreciate this difference between near and far depth signals on border ownership has led to erroneous claims about figure-ground perception.
