Phenomenal Slant as a Function of Ambiguity of Contour Perspective 1

Abstract

Os judged the slants of a rectangle and three trapezoids, with complete and broken outlines, exposed under reduced viewing conditions at slants of 10°, 25°, 40°. All forms were of the same height and area. The smallest projective angular convergence of the sides of the frontal-parallel trapezoids was larger than that of the rectangle at its greatest slant. The slant estimates of the monocular and binocular groups for the trapezoids differed significantly; those for the rectangle did not. Os distinguished effectively between the rectangle and the trapezoids but not among the trapezoids. Estimates for particular forms with complete and broken outlines did not differ significantly. The data were interpreted as limiting the contour perspective theory of slant perception and as demonstrating a subjective shape influence in accordance with either the Helmholtzian or the Gestaltist type of explanation.

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