Shape and depth perception from parallel projections of three-dimensional motion.

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Interpolation across orientation discontinuities in simulated three-dimensional (3-D) surfaces was studied in three experiments with the use of structure-from-motion (SFM) displays. The displays depicted dots on two slanted planes with a region devoid of dots (a gap) between them. If extended through the gap at constant slope, the planes would meet at a dihedral edge. Subjects were required to place an SFM probe dot, located within the gap, on the perceived surface. Probe dot placements indicated that subjects perceived a smooth surface connecting the planes rather than a surface with a discontinuity. Probe dot placements varied with slope of the planes, density of the dots, and gap size, but not with orientation (horizontal or vertical) of the dihedral edge or of the axis of rotation. Smoothing was consistent with models of 2-D interpolation proposed by Ullman (1976) and Kellman and Shipley (1991) and with a model of 3-D interpolation proposed by Grimson (1981). Wallach and O'Connell (1953) demonstrated that if subjects are shown the two-dimensional (2-D) shadow cast by a clear glass sphere that has small opaque dots on its surface and rotates about a vertical axis, then subjects perceive a spherical surface. A similar perception is commonly reported for computer-generated displays in which dots move about on a computer screen in a manner consistent with their being projections of dots on a rotating sphere (see, e.g., Braunstein, 1966;Braunstein & Andersen, 1984). Apparently human vision is adept at inferring 3-D structure from the 2-D motions of projected features. This process of inferring 3-D structure from 2-D motions, referred to as structure from motion (SFM) after Ullman (1979), has been studied extensively since the advent of computer-generated displays. (For reviews, see Braunstein, 1978Braunstein, , 1983Braunstein, , 1988 In many displays of SFM in which dots alone are projected on the computer screen, observers report seeing more than just a 3-D structure for the dots. They report, in addition, that they perceive a continuous surface in 3-D passing through, or near, the dots. Such perceptions of "subjective surfaces" on the basis of sparse collections of dots are not limited to SFM displays. Subjective surfaces have also been reported,

mentioning

confidence: 68%

Interpolation across surface discontinuities in structure from motion Asad Satdpour

Saidpour

Braunstein

Hoffman

1994

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“…The organization of texture elements along meridian lines does reduce the heterogeneity of velocities. Such reductions have been found to reduce the perceived depth in kinetic depth effect displays (Braunstein & Andersen, 1984). However, all observers reported perceiving the stimuli as spheres in the y-axis conditions (some perceived the z-axis stimuli as disks).…”

Section: Notementioning

confidence: 90%

Factors influencing perceived angular velocity

Kaiser

Calderone

1991

The assumption that humans are able to perceive and process angular kinematics is critical to many structure-from-motion and optical flow models. The current studies investigate this sensitivity, and examine several factors likely to influence angular velocity perception. In particular, three factors are considered: (1)the extent to which perceived angular velocity is determined by edge transitions of surface elements, (2) the extent to which angular velocity estimates are influenced by instantaneous linear velocities of surface elements, and (3)whether element-velocity effects are related to three-dimensional (3-D) tangential velocities or to two-dimensional (2-D) image velocities. Edge-transition rate biased angular velocity estimates only when edges were highly salient. Element velocities influenced perceived angular velocity; this bias was related to 2-D image velocity rather than 3-D tangential velocity. Despite these biases, however, judgments were most strongly determined by the true angular velocity. Sensitivity to this higher order motion parameter was surprisingly good, for rotations both in depth (y-axis) and parallel to the line of sight (z-axis).

“…Sperling et al (1989) used a fInite set of 53 different 3-D shapes in a shape identifIcation task, but did not report quantitative differences in performance for different 3-D shapes. Braunstein and Andersen (1984) noted that spheres, for example, might have certain heuristic topological characteristics that would make them special objects, not suitable for a generalization to other 3-D objects. It has to be examined yet what exactly these "heuristic" properties are.…”

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confidence: 99%

Discrimination of 3-D shape and 3-D curvature from motion in active vision

Damme

Oosterhoff

Grind

1994

We examined the ability of human observers to discriminate between different 3-D quadratic surfaces defined by motion, and with head position fed back to the stimulus to provide an up-todate dynamical perspective view. We tested whether 3-D shape or 3-D curvature would affect discrimination performance. It appeared that discrimination of 3-D quadratic shape clearly depended on shape but not on the amount of curvature. Even when the amount of curvature was randomized, subjects' performance was not altered. On the other hand, the discrimination of 3-D curvature clearly depended linearly on curvature with Weber fractions of 20% on the average and, to a small degree, on 3-D shape. The experiment shows that observers can easily separate 3-D shape and 3-D curvature, and that Koenderink's shape index and curvedness provide a convenient way to specify shape. These results warn us against using just any arbitrary 3-D shape in 3-D shape perception tasks and indicate, for example, that emphasizing 3-D shape in computer displays by exaggerating curvature does not have any effect.Since Wallach and O'Connell (1953) demonstrated that three-dimensional (3-D) shape could be extracted from orthographic projections of rotating objects, there have been numerous studies of this phenomenon, which is commonly known as the kinetic depth effect. Such psychophysical studies include, for example, those on object rigidity (Todd, 1984), perceived depth or curvature (Dosher, Landy, & Sperling, 1989;Norman & Lappin, 1992;Saidpour, Braunstein, & Hoffman, 1992), minimal conditions for the perception of 3-D shape from motion in multidot displays (Sperling, Landy, Dosher, & Perkins, 1989;Todd & Norman, 1991;Treue, Husain, & Andersen, 1991), projection methods (Todd, 1984), and token dependency (Landy, Dosher, Sperling, & Perkins, 1991).The most common way to study the phenomenon of 3-D shape from motion is to use random dot cinematograms of moving 3-D objects. The objects under study are mostly cylinders, planes, or spheres. There is no reason to assume that the results of these studies hold for all kinds of 3-D shapes, but most studies have not included a wide range of shapes or curvature values. On the other hand, the importance of a multiobject study has been pointed out by several authors. Norman and Lappin (1992) reported differences in discriminability between cylinders and spheres, spheres and planes, and cylinders and planes. for example, might have certain heuristic topological characteristics that would make them special objects, not suitable for a generalization to other 3-D objects. It has to be examined yet what exactly these "heuristic" properties are. It is well possible that a certain systematic 3-D shape dependency in structure from motion is responsible for this effect. A quantitative examination of 3-D shape perception obviously requires a mathematical defInition on-D shape. On the other hand, if we want to study 3-D shape perception in psychophysical experiments, this definition must be in some way ecologically valid so that ...