Perception of objects that are translating and rotating

The motion of objects that are both translating and rotating can be decomposed into an infinite number of translational and rotational combinations. How, then, do such stimuli routinely elicit specific percepts and behavioral responses that are usually appropriate? A possible answer is that motion percepts are fully determined by the probability distributions of all the possible correspondences and differences in the stimulus sequence. To test the merits of this conceptual framework, we investigated the perceived motion elicited by a line that is both translating and rotating behind an aperture. When stimuli are presented such that a particular sequence of appearance and disappearance occurs at the aperture boundary, subjects report that the line is rotating only; furthermore, the perceived centers of rotation appear to describe a cycloidal trajectory, even when one aperture shape is replaced by another. These and other perceptual effects elicited by translating and rotating stimuli are all accurately predicted by the probability distribution of the possible sources of the physical movements, supporting the conclusion that motion perception is indeed generated by a wholly probabilistic strategy.     

Perceptual linkage of multiple objects rotating in depth

When multiple objects rotate in depth, they are frequently perceived to rotate in the same direction even when perspective information signals counterrotation. Three experiments are reported on this tendency to recover the rotation directions of multiple objects in a nonindependent fashion (termed rotational linkage). Rotational linkage was strongly affected by slant in depth of the objects, image perspective, and relative starting phase of the objects. Linkage was found not to vary as a function of the relative rotation speed of the objects or the relative alignment of their rotation axes. Rotational linkage is interpreted as a tendency of the visual system to assign signed depths to objects based on a communality of image point direction.     

Perceived depth of 3-D objects in 3-D scenes

Effects of information specifying the position of an object in a 3-D scene were investigated in two experiments with twelve observers. To separate the effects of the change in scene position from the changes in the projection that occur with increased distance from the observer, the same projections were produced by simulating (a) a constant object at different scene positions and (b) different objects at the same scene position. The simulated scene consisted of a ground plane, a ceiling plane, and a cylinder on a pole attached to both planes. Motion-parallax scenes were studied in one experiment; texture-gradient scenes were studied in the other. Observers adjusted a line to match the perceived internal depth of the cylinder. Judged depth for objects matched in simulated size decreased as simulated distance from the observer increased. Judged depth decreased at a faster rate for the same projections shown at a constant scene position. Adding object-centered depth information (object rotation) increased judged depth for the motion-parallax displays. These results demonstrate that the judged internal depth of an object is reduced by the change in projection that occurs with increased distance, but this effect is diminished if information for change in scene position accompanies the change in projection.     

A structural analysis of stability in the perceived form of objects rotating in depth

Summary The stability and form of the two different appearances of a simple rotating object were explained by considering both the geometric transformations interrelating these appearances and their degree of organization. The analysis was then used to guide the construction of two complex rotating objects each expected to have multiple appearances. The results of an experiment confirmed the predicted form of the objects' initial appearances (illusory), the relative stability in time of these appearances and the form of the subsequent appearances (also illusory). The veridical appearances were never seen despite continued observation during two 10 min periods.We wish to thank P. Hamilton, A. Pearsall, A. Vadum, and H. Vadum for their help with this research. Requests for reprints should be sent to the first author at 1 Howatson Way, Worcester, Massachusetts, 01609, USA     

Kinetic contours in rotating objects

Kinetic contours seen in rotating objects provide evidence about contour function in a kinetic condition. It was observed that (i) when an object with an arc-shaped edge in its outline is rotated, a kinetic contour arises from the rotating arc and bounds a 'figure'; (ii) the kinetic contour not only protects the enclosed area of this figure from the destruction caused by motion, but also interrupts the continuity of the surroundings; (iii) kinetic contours are generally perceived to be organized into discs which appear as amodally completed forms in such a way that one object is hidden behind the other. The fact that oval or outline figures rarely produce kinetic contours is assumed to be due to figural self-sufficiency, which does not require perceptual completion through motion.     

Explicit and implicit memory for rotating objects

Although both the object and the observer often move in natural environments, the effect of motion on visual object recognition ha not been well documented. The authors examined the effect of a reversal in the direction of rotation on both explicit and implicit memory for novel, 3-dimensional objects. Participants viewed a series of continuously rotating objects and later made either an old-new recognition judgment or a symmetric-asymmetric decision. For both tasks, memory for rotating objects was impaired when the direction of rotation was reversed at test. These results demonstrate that dynamic information can play a role in visual object recognition and suggest that object representations can encode spatiotemporal information.     

Perceived orientation in depth from line-of-sight movement

Twelve college students viewed computer-generated displays of a cross comprised of two orthogonal dotted lines, and judged the apparent in-depth orientation of the horizontal arm by positioning a horizontal bar mounted on a rotary potentiometer. The vertical arm of the simulated cross was always in the observer’s frontal plane, but the randomly textured horizontal arm was in one of nine orientations relative to the line of sight. Each observer viewed displays in which the simulated cross was, alternately, (a) stationary, (b) approaching the viewer, and (c) stationary but expanding in size. The static texture density gradient in the horizontal arm of the simulated stationary cross mediated perceived orientation in depth. Further, when motion perspective was added to the detail perspective, the impression of depth was enhanced, with the greatest enhancement obtaining at the near viewing distance. When dynamic magnification was added to the detail perspective, the impression of depth was attenuated; this effect was interpreted as an illusory case of motion perspective.     

Preference for rotating objects in 5-month-old infants

Five-month-olds were habituated to several objects undergoing a variety of rotations or nonrotations. The test trials presented a new object undergoing examples of the old and new motions. Without exception, infants preferred the rotating object on the test trials, regardless of their previous experience.     

Visual inertia of rotating 3-D objects

Five experiments were designed to determine whether a rotating, transparent 3-D cloud of dots (simulated sphere) could influence the perceived direction of rotation of a subsequent sphere. Experiment 1 established conditions under which the direction of rotation of a virtual sphere was perceived unambiguously. When a near-far luminance difference and perspective depth cues were present, observers consistently saw the sphere rotate in the intended direction. In Experiment 2, a near-far luminance difference was used to create an unambiguous rotation sequence that was followed by a directionally ambiguous rotation sequence that lacked both the near-far luminance cue and the perspective cue. Observers consistently saw the second sequence as rotating in the same direction as the first, indicating the presence of 3-D visual inertia. Experiment 3 showed that 3-D visual inertia was sufficiently powerful to bias the perceived direction of a rotation sequence made unambiguous by a near-far luminance cue. Experiment 5 showed that 3-D visual inertia could be obtained using an occlusion depth cue to create an unambiguous inertia-inducing sequence. Finally, Experiments 2, 4, and 5 all revealed a fast-decay phase of inertia that lasted for approximately 800 msec, followed by an asymptotic phase that lasted for periods as long as 1,600 msec. The implications of these findings are examined with respect to motion mechanisms of 3-D visual inertia.     

Perceived depth in the 'sieve effect' and exclusive binocular rivalry

An impression of a surface seen through holes is created when one fuses dichoptic pairs of discs, with one member of each pair black and the other member white. This is referred to as the 'sieve effect'. The stimulus contains no positional disparities. Howard (1995, Perception 24 67-74) noted qualitatively that the sieve effect occurs when the rivalrous regions are within the range of sizes, contrasts, and relative sizes where exclusive rivalry occurs, rather than binocular lustre, stimulus combination, or dominant rivalry. This suggests that perceived depth in the sieve effect should be at a maximum when exclusive rivalry is most prominent. We used a disparity depth probe to measure the magnitude of perceived depth in the sieve effect as a function of the sizes, contrasts, and relative sizes of the rivalrous regions. We also measured the rate of exclusive rivalry of the same stimuli under the same conditions. Perceived depth and the rate of exclusive rivalry were affected in the same way by each of the three variables. Furthermore, perceived depth and the rate of exclusive rivalry were affected in the same way by changes in vergence angle, although the configuration of the stimulus surface was held constant. These findings confirm the hypothesis that the sieve effect is correlated with the incidence of exclusive rivalry.     

Perceived depth scales with disparity gradient.

Perceived difference in depth between two adjacent stimuli decreases with increasing disparity gradient even if the disparity stays constant, ie when the stimuli approach each other along paths within fronto-parallel planes. This depth scaling effect is more pronounced with line stimuli than with two isolated points or two small symbols and is insignificant for easily discriminable symbols. The decrease in perceived depth is more pronounced for horizontal orientation than for oblique or vertical orientation. The ratio of perceived depth difference to displayed disparity difference also decreases when the distance between the stimuli increases at a constant gradient in depth. This is to say that we are more correct in our depth estimates for steep gradients in depth when the euclidean distance between the stimuli is short.     

The visual representation of three-dimensional, rotating objects.

Depth rotations can reveal new object parts and result in poor recognition of "static" objects (Biederman & Gerhardstein, 1993). Recent studies have suggested that multiple object views can be associated through temporal contiguity and similarity (Edelman & Weinshall, 1991; Lawson, Humphreys & Watson, 1994; Wallis, 1996). Motion may also play an important role in object recognition since observers recognize novel views of objects rotating in the picture plane more readily than novel views of statically re-oriented objects (Kourtzi & Shiffrar, 1997). The series of experiments presented here investigated how different views of a depth-rotated object might be linked together even when these views do not share the same parts. The results suggest that depth rotated object views can be linked more readily with motion than with temporal sequence alone to yield priming of novel views of 3D objects that fall in between "known" views. Motion can also enhance path specific view linkage when visible object parts differ across views. Such results suggest that object representations depend on motion processes.     

Perceived depth vs. structural relevance in the object-superiority effect

When subjects must identify a barely visible line in a briefly flashed display, their accuracy depends on the configuration of the context in which the target line appears. Weisstein and Harris (1974) found that accuracy is highest when the target is part of a pattern that resembles a unified, three-dimensional object, and lowest in a flat-looking pattern composed of disconnected lines; they labeled this phenomenon the object-superiority effect. In the three experiments reported here, identification accuracy was found to correlate highly and significantly (r =.78) with the judged depth of the patterns. Judged structural relevance of the target line to the pattern (McClelland & Miller, 1979) was uncorrelated with accuracy (r=?.28). Even when the target line appeared as an isolated fragment within the context pattern, a pattern perceived as three-dimensional yielded higher identification accuracy than one perceived as flat.     

Perceived size of familiar objects and the theory of off-sized perceptions

In three experiments, I examined the claim (Gogel, 1969; Gogel & Newton 1969)that familiar objects viewed under reduced stimulus conditions frequently appear to be off-sized (i.e., larger or smaller.than normal). In Experiments 1 and 2, I presented images ofdifferent familiar objects, one at a time, at distances of .1. and 2 m from the observers. The images were normal-, large-, or small-sized versions of familiar objects, and the observers judged the perceived size of each object rela.tive to its familiar normal size. In Experiment 3, I presented normal-, large-, and small-sized versions of thesame familiar object at physical distances of 1 and 2 m. The pattern of size results was similar across the three experiments. In general, normal-sized objects appeared normal to small-sized at the 1-mdistance and small-sized at the 2-mdistance; small-sized objects appeared small-sized at the 1-m distance and even smaller at the 2-m distance; and large-sized objects appeared normal- to large-sized at the 1-m distance and normal- to small-sized at the 2-m distance. The distance results of Experiment 3 indicated that familiar size was an effective determinant of reported distance. These results are consistent with Gogel’s theory of off-sized perceptions and, more generally, with the claim that familiar size is not an important determinant of perceived size.