Necessity of spatial pooling for the perception of heading in nonrigid environments.

This study examined whether the perception of heading is determined by spatially pooling velocity information. Observers were presented displays simulating observer motion through a volume of 3-D objects. To test the importance of spatial pooling, the authors systematically varied the nonrigidity of the flow field using two types of object motion: adding a unique rotation or translation to each object. Calculations of the signal-to-noise (observer velocity-to-object motion) ratio indicated no decrements in performance when the ratio was .39 for object rotation and .45 for object translation. Performance also increased with the number of objects in the scene. These results suggest that heading is determined by mechanisms that use spatial pooling over large regions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rotational object discrimination by pigeons.

Four experiments examined the discrimination of directional object motion by pigeons. Four pigeons were tested in a go/no-go procedure with video stimuli of geons rotating right or left around their central y-axis. This directional discrimination was learned in 7 to 12 sessions and was not affected by changes in object starting orientation, but did require the coherent ordering of the videos’ successive frames. Subsequent experiments found no or little transfer of this motion discrimination to novel objects. Experiments varying the speed of rotation and degrees of apparent motion per frame revealed that both factors strongly affected the discrimination. Finally, tests with partial occlusion of different portions of a rotating object suggested that the majority of the object was likely involved in determining rotational direction. These experiments indicate that pigeons can exclusively use motion cues to judge relative object motion. They also suggest the pigeons may have used a specific representation of the motion sequences of each object to make the discrimination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The perception of depth through motion.

Motion perspective is the phenomenon that as an object moves, the projections of its surface features and of its contours undergo certain regular transformations. The retinal image undergoes similar transformations. This aspect of depth perception has received comparatively little attention. Theory has been primarily based on gestalt formulations, and, more recently, an empirical approach has been suggested which is based on the use of high speed computers. The latter approach appears quite promising. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aging and the Perception of Depth and 3-D Shape From Motion Parallax.

The ability of younger and older observers to perceive 3-D shape and depth from motion parallax was investigated. In Experiment 1, the observers discriminated among differently curved 3-dimensional (3-D) surfaces in the presence of noise. In Experiment 2, the surfaces' shape was held constant and the amount of front-to-back depth was varied; the observers estimated the amount of depth they perceived. The effects of age were strongly task dependent. The younger observers' performance in Experiment 1 was almost 60% higher than that of the older observers. In contrast, no age effect was obtained in Experiment 2. Older observers can effectively perceive variations in depth from patterns of motion parallax, but their ability to discriminate 3-D shape is significantly compromised. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Object manipulation and motion perception: Evidence of an influence of action planning on visual processing.

In 3 experiments, the authors investigated the bidirectional coupling of perception and action in the context of object manipulations and motion perception. Participants prepared to grasp an X-shaped object along one of its 2 diagonals and to rotate it in a clockwise- or a counterclockwise direction. Action execution had to be delayed until the appearance of a visual go signal, which induced an apparent rotational motion in either a clockwise- or a counterclockwise direction. Stimulus detection was faster when the direction of the induced apparent motion was consistent with the direction of the concurrently intended manual object rotation. Responses to action-consistent motions were also faster when the participants prepared the manipulation actions but signaled their stimulus detections with another motor effector (i.e., with a foot response). Taken together, the present study demonstrates a motor-visual priming effect of prepared object manipulations on visual motion perception, indicating a bidirectional functional link between action and perception beyond object-related visuomotor associations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A theory of dynamic occluded and illusory object perception.

Humans see whole objects from input fragmented in space and time, yet spatiotemporal object perception is poorly understood. The authors propose the theory of spatiotemporal relatability (STR), which describes the visual information and processes that allow visible fragments revealed at different times and places, due to motion and occlusion, to be assembled into unitary perceived objects. They present a formalization of STR that specifies spatial and temporal relations for object formation. Predictions from the theory regarding conditions that lead to unit formation were tested and confirmed in experiments with dynamic and static, occluded and illusory objects. Moreover, the results support the identity hypothesis of a common process for amodal and modal contour interpolation and provide new evidence regarding the relative efficiency of static and dynamic object formation. STR postulates a mental representation, the dynamic visual icon, that briefly maintains shapes and updates positions of occluded fragments to connect them with visible regions. The theory offers a unified account of interpolation processes for static, dynamic, occluded, and illusory objects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Accuracy and precision of binocular 3-D motion perception.

In principle, information for 3-D motion perception is provided by the differences in position and motion between left- and right-eye images of the world. It is known that observers can precisely judge between different 3-D motion trajectories, but the accuracy of binocular 3-D motion perception has not been studied. The authors measured the accuracy of 3-D motion perception. In 4 different tasks, observers were inaccurate, overestimating trajectory angle, despite consistently choosing similar angles (high precision). Errors did not vary consistently with target distance, as would be expected had inaccuracy been due to misestimates of viewing distance. Observers appeared to rely strongly on the lateral position of the target, almost to the exclusion of the use of depth information. For the present tasks, these data suggest that neither an accurate estimate of 3-D motion direction nor one of passing distance can be obtained using only binocular cues to motion in depth. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

When the target becomes the mask: Using apparent motion to isolate the object-level component of object substitution masking.

J. T. Enns and V. Di Lollo (1997) discovered a new form of visual masking that they labeled object substitution masking (OSM). OSM occurs when 4 dots, presented around a target, trail in the display after target offset. The present study showed that the physical presence of the masking dots after target offset is not necessary for OSM. Instead, the continued presence of a changing high-level representation associated with the target suffices to yield OSM. Apparent motion was used to define such representation. In these experiments, the initial display offset and was followed by a 2nd display where masks appeared at new locations. Only when the spatiotemporal properties of the stimuli on the 2nd display supported the perception of the target moving and turning into the mask was OSM observed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Introduction to the special issue on object perception and scene analysis.

Work in psychophysics, neuroscience, and visual perception has led to significant recent advances in our understanding of the human visual system. The articles in this special issue represent diverse approaches to the study of visual perception and highlight some of these recent advances, as applied to issues involved in understanding object perception and scene analysis. The special issue grew out of a workshop on object and scene perception held in September 1990 at the University of Leuven. The intent of the original workshop and of the collection of articles in this issue is to bring together the work of researchers using widely differing techniques and theoretical frameworks, and to apply recent results to the issues surrounding object and scene perception. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Edge-region grouping in figure-ground organization and depth perception.

Edge-region grouping (ERG) is proposed as a unifying and previously unrecognized class of relational information that influences figure-ground organization and perceived depth across an edge. ERG occurs when the edge between two regions is differentially grouped with one region based on classic principles of similarity grouping. The ERG hypothesis predicts that the grouped side will tend to be perceived as the closer, figural region. Six experiments are reported that test the predictions of the ERG hypothesis for 6 similarity-based factors: common fate, blur similarity, color similarity, orientation similarity, proximity, and flicker synchrony. All 6 factors produce the predicted effects, although to different degrees. In a 7th experiment, the strengths of these figural/depth effects were found to correlate highly with the strength of explicit grouping ratings of the same visual displays. The relations of ERG to prior results in the literature are discussed, and possible reasons for ERG-based figural/depth effects are considered. We argue that grouping processes mediate at least some of the effects we report here, although ecological explanations are also likely to be relevant in the majority of cases. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Counter-changing luminance: A non-Fourier, nonattentional basis for the perception of single-element apparent motion.

Motion perception was studied for generalized apparent motion stimuli composed of 2 simultaneously visible elements whose luminance alternated between 2 values (only 1 element is visible at a time for standard apparent motion). It was demonstrated that 1st-order motion energy is neither necessary nor sufficient for the perception of apparent motion. Instead, it was found that counter-changing luminance--simultaneous luminance changes at 2 element locations--is the informational basis for perceiving luminance-defined apparent motion: Motion starts where luminance changes toward the background luminance value and ends where luminance changes away from the background luminance. The results were not attributable to either 2nd-order motion mechanisms (for which rectification precedes the computation of motion energy) or attention-based, 3rd-order motion mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Is binocular correspondence and disparity still a dominant factor in binocular depth perception?

Laws of binocular correspondence and disparity are regarded as bases for explanation of most of the phenomena of binocular depth perception in the near field of vision. Abnormal phenomena such as differences in astigmatism of the 2 eyes, differences in acuity, cases of natural aniseikonia, investigated by the author, confirm the validity of the laws of correspondence and disparity and also of the law of intersection of visual directional lines. The inadequacies of other theories of binocular depth perception are pointed out and the author concludes that they cannot supplant the laws of binocular correspondence and disparity for the great majority of cases of binocular perception of depth in the near field of vision. (46 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Orientation effects in visual object perception: Recent results that will make your mind spin!

The time needed to identify objects from two-dimensional depictions can be affected sharply by the orientation of the depicted object. Although it is suspected that the magnitude of orientation effects on identification from drawings ought to depend on various characteristics of the objects and of the depictions, almost nothing is known about these relationships. Work in progress in my laboratory is designed to discover which characteristics of objects and depictions lead to large or small effects of orientation and which lead to peaked functions versus dipped functions. The results are summarized in this article. Overall, the results suggest that orientation effects take place at a perceptual stage of processing that is distinct from subsequent stages involved in retrieving a name and producing a response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanical invariants are implicated in dynamic touch as a function of their salience in the stimulus flow.

The authors investigated the mechanical basis of length perception through dynamic touch using specially designed rods in which the various moments of mass distribution (mass, static moment, and rotational inertia) were varied independently. In a series of 4 experiments, exploration style and rod orientation were manipulated such that the relative salience of moments of mass distribution varied markedly. Results showed that perceived length was based on the most salient moments. The authors concluded that the notion of salience is crucial for understanding the implication of moments of mass distribution in length perception and that it should play a pivotal role in developing an encompassing theory of dynamic touch. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The figure ground problem in motion perception.

Perceiving motion in an object involves discriminating the object from its background, judging the motion contrast between figure and ground and then attributing the motion to the appropriate entity. The present paper discusses psychophysical data on Induced Motion (IM) which supports the view that object/motion perception is constructed relatively late in the system by combining the output of several different motion analysers. Results from two experiments suggest that solution of the figure ground problem in motion perception may occur late in processing, be mediated by the parvocelluar stream and involve combining the output of at least two types of motion analysers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Processing of biological motion point-light displays by baboons (Papio papio).

Humans apply complex conceptual judgments to point-light displays (PLDs) representing biological motion (BM), but how animals process this kind of display remains uncertain. Four baboons (Papio papio) were trained to discriminate BM from nonbiological motion PLDs using an operant computerized test system. Transfer tests were given after training with novel BM stimuli representing humans or baboons (Experiment 1), with inverted PLDs (Experiment 2), and with BM stimuli in which body parts had been spatially disorganized (Experiment 3). Very limited transfer was obtained with the novel and inverted displays in Experiments 1 and 2, but transfer was much higher after spatial disorganization in Experiment 3. It is suggested that the baboons did not retrieve and interpret the articulated shape of the human or monkey body from the BM PLD stimuli, but rather focused their attention on the configural properties of subparts of the stimuli. Limits in perceptual grouping and restricted abilities in picture-object equivalence might explain why the baboons did not map BM PLD displays onto what they represent. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceiving motion while moving: How pairwise nominal invariants make optical flow cohere.

Computer-generated sequences simulated observer movement toward 10 randomly placed poles, 1 moving and 9 stationary. When observers judged their direction of movement, or heading, they used 3 related invariants: The (a) convergence and (b) decelerating divergence of any 2 poles specified that heading was to the outside of the nearer pole, and the (c) crossover of 2 poles specified that heading was to the outside of the farther pole. With all poles stationary, the field of 45 pairwise movements yielded a coherent specification of heading. With 1 pole moving with respect to the others, however, the field a could yield an incoherent heading solution. Such incoherence was readily detectable; similar pole motion leading to coherent flow, however, was less readily detectable. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What does visual agnosia tell us about perceptual organization and its relationship to object perception?

The authors studied 2 patients, S.M. and R.N., to examine perceptual organization and its relationship to object recognition. Both patients had normal, low-level vision and performed simple grouping operations normally but were unable to apprehend a multielement stimulus as a whole. R.N. failed to derive global structure even under optimal stimulus conditions, was less sensitive to grouping by closure, and was more impaired in object recognition than S.M. These findings suggest that perceptual organization involves a multiplicity of processes, some of which are simpler and are instantiated in lower order areas of visual cortex (e.g., collinearity). Other processes are more complex and rely on higher order visual areas (e.g., closure and shape formation). The failure to exploit these latter configural processes adversely affects object recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The bicycle illusion: Sidewalk science informs the integration of motion and shape perception.

The authors describe a new visual illusion first discovered in a natural setting. A cyclist riding beside a pair of sagging chains that connect fence posts appears to move up and down with the chains. In this illusion, a static shape (the chains) affects the perception of a moving shape (the bicycle), and this influence involves assimilation (averaging) rather than opposition (differentiation). These features distinguish the illusion from illusions of motion capture and induced motion. The authors take this bicycle illusion into the laboratory and report 4 findings: Na?ve viewers experience the illusion when discriminating horizontal from sinusoidal motion of a disc in the context of stationary curved lines; the illusion shifts from motion assimilation to motion opposition as the visual size of the display is increased; the assimilation and opposition illusions are dissociated by variations in luminance contrast of the stationary lines and the moving disc; and the illusion does not occur when simply comparing two stationary objects at different locations along the curved lines. The bicycle illusion provides a unique opportunity for studying the interactions between shape and motion perception. (PsycINFO Database Record (c) 2010 APA, all rights reserved)