Abstract
Purpose: Two-dimensional (2D) drawings of scenes that depict strong perspective depth appear to stretch and shear as a viewer moves in front of them. Likewise, when such drawings are rotated away from a frontoparallel orientation, a stationary viewer perceives similar stretches and shears. Our goal is to characterize these deformations quantitatively and to examine whether prolonged viewing of a rotated scene causes adaptation that makes the scene to appear deformed when presented on the frontoparallel plane after adaptation. Methods: We used two types of scenes, containing polyhedral surfaces, with either (a) a convex object, or (b) a concave space. These scenes were shown monocularly to observers either on the frontoparallel plane, or in oblique orientations of various tilts. The observers' task was to adjust the location of a critical edge in the scene, to compensate for the perceived deformation, until they perceived two test planar surfaces to be of equal width on the plane of the drawing. The magnitude of the edge displacement served as a measure of the deformation. Results: When the adjusted critical edge was the apex of a convex dihedral angle formed by the two test planes in the perceived three-dimensional (3D) space, then, upon rotation of the image, the plane nearer to the observer appeared to be significantly narrower than the far plane. In contrast, when the critical edge was the apex of a concave angle formed by the test planes in 3D space, then the near plane appeared to be significantly wider than the far plane. The magnitude of the effect was a monotonic function of the tilt angle in both cases. Adaptation to a rotated view of an image caused the test image, subsequently presented on the frontoparallel plane, to appear deformed in the direction opposite to that perceived in the adapting image. Conclusion: Monocular 3D cues that are present in a 2D image strongly affect how the shape of the image is perceived from different viewing directions.
This work was supported by NIH/NEI grant R01 EY 013758-01