The accuracy of depth judgments that are based on binocular disparity or structure from motion (motion parallax and object rotation) was studied in 3 experiments. In Experiment 1, depth judgments were recorded for computer simulations of cones specified by binocular disparity, motion parallax, or stereokinesis. In Experiment 2, judgments were recorded for real cones in a structured environment, with depth information from binocular disparity, motion parallax, or object rotation about the y-axis. In both of these experiments, judgments from binocular disparity information were quite accurate, but judgments on the basis of geometrically equivalent or more robust motion information reflected poor recovery of quantitative depth information. A 3rd experiment demonstrated stereoscopic depth constancy for distances of 1 to 3 m using real objects in a well-illuminated, structured viewing environment in which monocular depth cues (e.g., shading) were minimized. It has been pointed out that the geometric information supporting the perception of depth from binocular disparity is actually less determinate than that supporting the recovery of structure from object rotation or motion parallax

This paper addresses the computational role that the construction of a complete surface representation may play in the recovery of 3-D structure from motion. We first discuss the need to integrate surface reconstruction with the structure-from-motion process, both on computational and perceptual grounds. We then present a model that combines a feature-based structure-from-motion algorithm with a smooth surface interpolation mechanism. This model allows multiple surfaces to be represented in a given viewing direction, incorporates constraints on surface structure from object boundaries, and segregates image features onto multiple surfaces on the basis of their 2-D image motion. We present the results of computer simulations that relate the qualitative behavior of this model to psychophysical observations. In a companion paper, we discuss further perceptual observations regarding the possible role of surface reconstruction in the human recovery of 3-D structure from motion. Three-dimensional structure-from-motion perception Temporal integration Surface reconstruction Motion interpretation Motion

Sensitivity of 8-week-old infants to optical flow specifying the shape of a three-dimensional object was assessed. Infants viewed kinetic random-dot displays that specified three-dimensional cubes. The cubes were identical except for the presence or absence of an interior corner. Half of the infants viewed the full display. The other half viewed the central region of the displays, where the flow specifying the presence or absence of the corner differed. Infants in the full-view condition looked significantly longer to a novel cube than to the familiar cube following habituation. In contrast, infants in the partial-view condition looked equally to the novel and familiar cubes, ruling out the possibility that infants who viewed the full displays merely discriminated differences in motion in the central region of the two displays. These findings suggest that infants as young as 8 weeks perceive three-dimensional object shape from optic flow. Perception of the world based on motion has occupied perceptual psychologists for a number of decades (see Braunstein, 1962, for a review). Pioneering work by Helmholtz (1909/1924) suggested that the differential motion of objects located at different distances was an effective cue to depth, and informal experiments conducted

Perceived orientation of axis of rotation and accuracy in discriminating fixed-axis from nordixed-axis rotations were investigated for orthographic projections of three-dimensional rotating objects. The principal findings were (a) the slant of the axis of rotation was systematically misperceived; (b) in both two-view and multiview displays, the perceived slant of the axis of rotation was well-predicted by the ratio between the deformation (a property of the first-order optic flow) and the component parallel to the image plane of the global velocity vector; (c) if this ratio was kept constant in each frame transition of the stimulus sequence (or it was varied), then the stimuli tended to be judged as fixed-axis rotations (or as nonfixed-axis rotations), regardless of whether they simulated a fixed-axis rotation or not; and (d) the tilt of the axis of rotation was perceived in two-view displays with a very small error. A changing two-dimensional (2-D) projection of an object's motion gives rise to a compelling impression of a volumetric shape moving in three-dimensional (3-D) space. This phenomenon (called the kinetic depth effect [KDE] after Wallach & O'Cormell, 1953) represents an essential

Permission has been granted to: a) YORK UNIVER-SITY LIBRARIES to lend or sell copies of this dissertation in paper, microform or electronic formats, and b) LIBRARY AND ARCHIVES CANADA to reproduce, lend, distribute, or sell copies of this thesis anywhere in the world in microform, paper or electronic formats and to authorise or procure the reproduction, loan, distribution or sale of copies of this thesis anywhere in the world in microform, paper or electronic formats. The author reserves other publication rights, and neither the thesis nor extensive extracts for it may be printed or otherwise reproduced without the author’s written permission. MOTION MODEL: EXTENDING AND IMPROVING

Abstract-This paper otTers a quick review of the subject of “optic flow ” in its conceptual and computational aspects, The theory is evaluated in terms of possible applications in the neurophysiology and experimental psychology of spatial sensorymotor behaviour and perception. The problem of which kind of detector is suited to extract various aspects of optic tlow is given special attention. It is shown that the possibilities are actually much more various than is reflected in the current (even the frankly speculative) literature. It is argued that a system that is sensitive to the relative time changes of the orientation differences of image details is especially suited for an analysis of the optic flow with regard to the information concerning the three dimensional shape of objects such as is contained in the Ilow. Thus the orientation sensitive elements that are known to be abundantly present in the primary visual cortex of many vertebrates are hcrcby implicated as a quite likely substrate for the extraction of the solid shape ofenvironmental objects. In our opinion this possibility should be investigated with the same ardour as the usual interpretation, which holds this system responsible for the initial extraction of the contours of flat (i.e. defined in the image) shapes. A new, partial solution to the “structure from motion problem” is offered, that not only covers the usual case of shape extraction in the presence of rigid motions of the object, but also the much wider class of (non-rigid) bending deformations (such as occur in the non-rigid

Perceived orientation of axis of rotation and accuracy in discriminating fixed-axis from nordixed-axis rotations were investigated for orthographic projections of three-dimensional rotating objects. The principal findings were (a) the slant of the axis of rotation was systematically misperceived; (b) in both two-view and multiview displays, the perceived slant of the axis of rotation was well-predicted by the ratio between the deformation (a property of the first-order optic flow) and the component parallel to the image plane of the global velocity vector; (c) if this ratio was kept constant in each frame transition of the stimulus sequence (or it was varied), then the stimuli tended to be judged as fixed-axis rotations (or as nonfixed-axis rotations), regardless of whether they simulated a fixed-axis rotation or not; and (d) the tilt of the axis of rotation was perceived in two-view displays with a very small error. A changing two-dimensional (2-D) projection of an object's motion gives rise to a compelling impression of a volumetric shape moving in three-dimensional (3-D) space. This phenomenon (called the kinetic depth effect [KDE] after Wallach & O'Cormell, 1953) represents an essential

3 explanations of apparent reversals (oscillation) of rotary motion in depth attribute this effect to misjudgment of orientation. These explanations are based mainly on observations of a trapezoidal "window " in rotation. The experiments reported here show that perspective effects in a trapezoidal window do not increase reversal frequencies and that other shapes in addition to a trapezoid exhibit the effect with similar frequencies. The experiments also failed to confirm that misjudgments of orientation are a causal condition of apparent reversals. A general theory in terms of an identity of projected (retinal) motion characteristics for clockwise and anticlockwise motion is proposed with supporting evidence. Apparent orientation is held to be a consequence of rather than a necessary condition for apparent reversal. This theory is sufficiently general to explain apparent reversals ("fluctuations") in the orientation in depth of static figures and objects and to explain also the kinetic depth effect. All these phenomena are held to derive from an identity of retinal projections for 2 or more motions or orientations of an object in space. Objects rotating in depth relative to an observer are frequently judged, usually with monocular vision, as apparently reversing their directions of rotary motion. Recession of a point or edge is sometimes reported as approach and vice versa. This effect, as far as is known, was first reported by Kenyon (1898) in the following terms: A curious illusion connected with an ordinary two-winged pendant fan.., consists in the fan appearing to rotate in the opposite direction.... Two other illusions... may be noted. In one the vanes, instead of rotating, seem to flap together; in the other the two arms appear to be continually withdrawing into and pushing out from the hanging rod [p. 371]. The effect was later mentioned by Miles (1929) and, more recently, extensively investigated by Ames (1951) who explained it in terms of assumptions consequent upon past experience