Psychophysical Hypothesis for Stationary Edge Perception
J. J. Gibson, Cornell University
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1. An occluding edge will tend to appear on the inside of a closed contour but not on the outside (Rubin’s principle of figure on ground. It can be extended to state that the more a contour tends to be closed(concave, or an acute angle) the more it will tend to appear as an occluding edge).
Exception: when the interior of a closed contour is textureless and the exterior is textured, an occluding edge tends to appear on the outside of the contour if the form is large enough. This follows from the general principle that any large enough sample of textureless light appears insubstantial. (Results of experiments on apertures, holes or windows, and with Metzger’s homogeneous field.)
2. When there is optical texture on one side of a contour but not on the other an occluding edge will tend to appear on the side with the texture.
Exception: when the contour is closed and the area enclosed is small the texture may be outside but the superposed edge will be on the inside (Katz). Likewise when the contour is shrunken to a spot it will appear in front.
Question: How are these principles interrelated?
Note that from this psychophysical point of view, Wertheimer’s “laws of grouping” do not refer to organization of sensory elements in the brain but to conditions for the perception of surfaces, to optical texture; and that the figure-ground phenomenon of Rubin is not an expression of a general tendency to experience objects (“forms”) but only of the optical information for the perception of an occluding edge.