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PubMed1997

The perception of motion and structure in structure-from-motion: comparisons of affine and Euclidean formulations.

I investigated the discrimination of rigid from nonrigid structure and the perception of affine stretches along the line of sight [Norman & Todd (1993). Perception and Psychophysics, 53, pp. 279-291]. Investigations of performance at discriminating rigid from nonrigid structure showed that performance improved when number of views and amount of simulated three-dimensional nonrigidity increased. Investigations of rotations about the vertical which include affine stretches along the line of sight compared Euclidean interpretations of affine-stretching stimuli to human perception. These Euclidean interpretations were obtained from a simple algorithm which recovered structure and motion from this limited class of stimuli under the assumption that distances to the axis of rotation did not change. The algorithm predicted that stretches along the line of sight would be perceived as nearly rigid and have variable angular velocity. These predictions were supported by subjects' reports of occurrences of nonrigidity and minima of angular velocity. The Euclidean algorithm also provided measures of nonrigidity and motion coherence, and experimental results were consistent with a prediction of when perception of nonrigidity would be independent of perception of coherence. The results are discussed relative to the advantages and shortcomings of both the affine and Euclidean approaches to structure-from-motion.

Algorithms↗
PubMed1992

Interactions between colour and luminance contrast in the perception of motion.

It has been demonstrated widely that at isoluminance moving chromatic stimuli are seen to be stationary or moving more slowly than their luminance counterparts. We have examined the effect on perceived velocity of adding luminance contrast to an isoluminant chromatic stimulus. We show that moving luminance contrast 'captures' colour so that a combined colour and luminance stimulus is seen moving as a unified percept. However, in the presence of colour contrast, significantly higher levels of luminance contrast are required to achieve a veridical velocity than for monochromatic stimuli with only luminance contrast. We show that this interactive effect between colour and luminance contrast cannot be fully explained by a threshold masking of luminance by colour contrast. The effect suggests that a breakdown in the veridical perception of velocity should be expected for colours with a wide range of associated luminance contrasts and not just for those at the point of isoluminance.

Color Perception↗
PubMed2005

Motion processing specialization in Williams syndrome.

Williams syndrome (WS) is a rare genetic disorder characterized by severe spatial deficits and relatively spared language. Although initial research suggested that WS entails a generalized motion processing deficit, later work demonstrated intact biological motion perception in people with WS, reflecting a sparing of a specific motion perception system. The present study examined whether this sparing is unique to biological motion, or extends to other motion tasks as well. WS children and adults and normal controls were tested to examine developmental changes across a variety of motion tasks. Results indicated that WS individuals performed at normal levels for motion coherence and biological motion tasks but had elevated thresholds for the 2-D form-from-motion task, a profile that extended into adulthood. These findings provide evidence that a genetic impairment can lead to a selective motion processing deficit and argue against characterizing WS as including a general motion processing impairment. The nature of the motion deficit is considered, including the implications for WS dorsal/ventral processing.

Adolescent↗
PubMed1996

Perception of motion smear in normal observers and in persons with congenital nystagmus.

PURPOSE: Despite incessant motion of the retinal image, persons with congenital nystagmus (CN) usually do not report that targets are smeared. The authors investigated whether the brief stationary glimpses of a target that occur during foveation periods in the CN waveform contribute to the alleviation of perceived smear. METHODS: Retinal image motion simulating that in jerk nystagmus was produced in normal observers (N = 10) who monocularly viewed either a 5-minute or a 1 degree luminous disk reflected from a horizontally oscillating mirror. Contrast sensitivities to detect each target and to perceive the presence of motion smear were determined for two simulated CN waveforms; observers also estimated the length and brightness of perceived smear for several suprathreshold target luminances. One waveform was a 7 degrees, 4-Hz ramp that included 120 msec zero-velocity intervals, simulating the foveation periods in the CN waveform. The second waveform lacked the zero-velocity simulated foveation periods. For comparison, estimates of perceived smear for physically stationary targets were obtained from three observers with CN. RESULTS: Normal observers' contrast sensitivities for perceiving smear were nearly identical for the simulated CN waveforms with and without a 120-msec foveation period. Estimated length and brightness of perceived smear for suprathreshold targets increased similarly with luminance for both waveforms. Observers with CN reported substantially less smear than did normal observers. CONCLUSIONS: Glimpses of a stationary retinal image during simulated foveation periods do not attenuate the perception of motion-induced smear in normal observers. In persons with CN, the perception of smear may be reduced by the extraretinal signals that accompany their eye movements.

Contrast Sensitivity↗
PubMed2001

Evolutionary internalized regularities.

Roger Shepard's proposals and supporting experiments concerning evolutionary internalized regularities have been very influential in the study of vision and in other areas of psychology and cognitive science. This paper examines issues concerning the need, nature, explanatory role, and justification for postulating such internalized constraints. In particular, I seek further clarification from Shepard on how best to understand his claim that principles of kinematic geometry underlie phenomena of motion perception. My primary focus is on the ecological validity of Shepard's kinematic constraint in the context of ordinary motion perception. First, I explore the analogy Shepard draws between internalized circadian rhythms and the supposed internalization of kinematic geometry. Next, questions are raised about how to interpret and justify applying results from his own and others' experimental studies of apparent motion to more everyday cases of motion perception in richer environments. Finally, some difficulties with Shepard's account of the evolutionary development of his kinematic constraint are considered.

Biological Evolution↗
PubMed2005

Time course and magnitude of illusory translation perception during off-vertical axis rotation.

Human spatial orientation relies on vision, somatosensory cues, and signals from the semicircular canals and the otoliths. The canals measure rotation, whereas the otoliths are linear accelerometers, sensitive to tilt and translation. To disambiguate the otolith signal, two main hypotheses have been proposed: frequency segregation and canal-otolith interaction. So far these models were based mainly on oculomotor behavior. In this study we investigated their applicability to human self-motion perception. Six subjects were rotated in yaw about an off-vertical axis (OVAR) at various speeds and tilt angles, in darkness. During the rotation, subjects indicated at regular intervals whether a briefly presented dot moved faster or slower than their perceived self-motion. Based on such responses, we determined the time course of the self-motion percept and characterized its steady state by a psychometric function. The psychophysical results were consistent with anecdotal reports. All subjects initially sensed rotation, but then gradually developed a percept of being translated along a cone. The rotation percept could be described by a decaying exponential with a time constant of about 20 s. Translation percept magnitude typically followed a delayed increasing exponential with delays up to 50 s and a time constant of about 15 s. The asymptotic magnitude of perceived translation increased with rotation speed and tilt angle, but never exceeded 14 cm/s. These results were most consistent with predictions of the canal-otolith-interaction model, but required parameter values that differed from the original proposal. We conclude that canal-otolith interaction is an important governing principle for self-motion perception that can be deployed flexibly, dependent on stimulus conditions.

Adaptation, Physiological↗
PubMed1979

Object perception and motion in infants.

Male and female infants 10 weeks of age (N = 24) were presented with two distinctively patterned objects in either moving or stationary form. Measures of visual regard indicated the infants were able to discriminate between the objects whether the objects were stationary or in motion. The results are contrasted to T. G. R. Bower's assessment of infants' utilization of features in perceiving moving objects. The results are also compared to those of an earlier study which employed an operant rather than a preference technique to investigate this same problem.

Discrimination, Psychological↗
PubMed1989

Max Wertheimer on seen motion: theory and evidence.

Max Wertheimer, the chief founder of an experimentally based Gestalt psychology, conducted his pioneering studies in motion perception on new theoretical grounds. Since the influence of this approach may be greater in today's cognitive psychology than it has ever been during the half-century of introspectionism and radical behaviorism, it is appropriate to review the actual roots of Wertheimer's (1912) seminal publication and his continuing research on apparent and real motion perception in the light of past and recent work. Illustrative examples, especially of Wertheimer's early research, are provided in this paper. The implications of his experimentation and biopsychological theorizing are still of major interest for present psychological inquiry. Nevertheless, the need for more future systematic comparative research on motion perception must be emphasized. The Epilogue of this paper examines why important parts of Wertheimer's experimental contributions to psychology may have been underrated or neglected by many contemporary psychologists.

Germany↗
PubMed1992

On the perception of shape from shading.

The extraction of three-dimensional shape from shading is one of the most perceptually compelling, yet poorly understood, aspects of visual perception. In this paper, we report several new experiments on the manner in which the perception of shape from shading interacts with other visual processes such as perceptual grouping, preattentive search ("pop-out"), and motion perception. Our specific findings are as follows: (1) The extraction of shape from shading information incorporates at least two "assumptions" or constraints--first, that there is a single light source illuminating the whole scene, and second, that the light is shining from "above" in relation to retinal coordinates. (2) Tokens defined by shading can serve as a basis for perceptual grouping and segregation. (3) Reaction time for detecting a single convex shape does not increase with the number of items in the display. This "pop-out" effect must be based on shading rather than on differences in luminance polarity, since neither left-right differences nor step changes in luminance resulted in pop-out. (4) When the subjects were experienced, there were no search asymmetries for convex as opposed to concave tokens, but when the subjects were naive, cavities were much easier to detect than convex shapes. (5) The extraction of shape from shading can also provide an input to motion perception. And finally, (6) the assumption of "overhead illumination" that leads to perceptual grouping depends primarily on retinal rather than on "phenomenal" or gravitational coordinates. Taken collectively, these findings imply that the extraction of shape from shading is an "early" visual process that occurs prior to perceptual grouping, motion perception, and vestibular (as well as "cognitive") correction for head tilt. Hence, there may be neural elements very early in visual processing that are specialized for the extraction of shape from shading.

Attention↗
PubMed2005

The perception of motion in chromatic stimuli.

The issue of whether there is a motion mechanism sensitive to purely chromatic stimuli has been pertinent for the past 30 or more years. The aim of this review is to examine why such different conclusions have been drawn in the literature and to reach some reconciliation. The review critically examines the behavioral evidence and concludes that there is a purely chromatic motion mechanism but that it is limited to the fovea. Examination of motion performance for chromatic and luminance stimuli provides convincing evidence that there are at least two different mechanisms for the two kinds of stimuli. The authors further argue that the chromatic mechanism may be at a particular disadvantage when the integration of multiple local motion signals is required. Finally, the authors present a descriptive model that may go some way toward explaining the reasons for the differences in collected data outlined in this article.

Color Perception↗
PubMed2004

Is precise discrimination of low level motion needed for heading discrimination?

Normal observers judge heading well both when moving in a straight line and when moving along a curved path. Judgments of curved path motion require depth variations in the scene while judgments of straight line heading (pure translation) do not. Here we show that a stroke patient who is impaired in low level 2D motion discrimination tasks and cannot accurately judge 3D structure from motion can accurately judge heading for straight line self-motion. This patient is impaired in judgments of curved path self-motion. This suggests that accurate heading judgments for observer translation do not require accurate 2D motion perception or 3D reconstruction of the scene. Judgments of curved path motion appear more dependent on accurate 2D motion perception.

Aged↗
PubMed1975

The relation between discrimination and sensitivity in the perception of motion in depth.

1. Binocular discrimination of the direction of a target's motion in depth was measured in terms of the smallest angular difference in direction that could be detected with a probability 50% better than chance. Directional discrimination was measured for targets moving along 16 different trajectories directed to the left and right of the nose. 2. The relative velocities of the retinal images in the left and right eyes gave a sensitive cue to the direction of the target's motion in depth. 3. The direction of motion was bets discriminated when the target moved along a line directed close to the nose. A change in direction of only 0.2 degrees from this direction of motion could be detected. Discrimination showed two other maxima, one on each side of the central maximum. Discrimination fell to about 0.6-0.8 degrees when the target's direction was changed by only 6 degrees to either side of the nose. 4. The curve of sensitivity to movement in depth had a generally inverse shape to the directional discrimination curve: sensitivity was minimal for trajectories directed near the nose and increased for trajectories directed so as to miss the head. 5. The directional discrimination curve can be related to the sensitivity curves of the four postulated neural mechanisms tuned to different directions of motion in depth; there are three discrimination maxima and, correspondingly, three trajectories for which the slopes of adjacent sensitivity curves differ maximally. This suggests that binocular psychophysical judgements of the direction along which a target moves in depth are to some extent mediated by neural mechanisms that compare (e.g. subtract) the outputs of directionally tuned movement detectors. One function of such neural comparators might be to enhance psychophysical sensitivity to the direction along which a target moves in depth, and thus to provide a physiological basis for precisely judging whether or not an object will hit the head. 6. We suggest that the neural basis for judging the direction of moving objects has an analogy in colour vision where opponent-colour mechanisms enhance sensitivity to wave-length differences in such a way that wave-lengths are more easily discriminated in those parts of the spectrum where the slopes of the pigment action spectra differ maximally.

Adaptation, Ocular↗
PubMed1995

Retinotopic and directional defects in motion discrimination in humans with cerebral lesions.

We investigated the discrimination of motion direction in peripheral and central vision in 23 patients with unilateral cerebral hemispheric lesions on computed tomography or magnetic resonance imaging. We used random dot cinematograms that determined a percent coherence motion threshold for 16 points in the peripheral field and for four directions separately in central vision. We measured asymmetry of right- versus left-field peripheral discrimination (retinotopic defects) and asymmetry of central discrimination for rightward versus leftward motion (directional defects), compared with normal subjects. Five patients had directional asymmetries of foveal motion perception, all worse for motion toward the side of their lesions. One patient had a bidirectional defect for the perception of horizontal motion. For 3 of these 6, the average of all horizontal and vertical motion discrimination thresholds was also elevated. Two had contralateral retinotopic defects. One of these also had an ipsidirectional foveal defect, but the other did not. The remaining 5 patients with ipsidirectional foveal defects had hemianopias that precluded testing for coexistent retinotopic defects. The lesions of the 6 patients with ipsidirectional defects overlapped in white matter underlying the lateral temporo-occipital cortex, at the junction of Brodmann areas 19 and 37. In contrast, lesions of patients without directional defects spared this region.

Adult↗
PubMed1999

Bayesian inference in populations of cortical neurons: a model of motion integration and segmentation in area MT.

A major issue in cortical physiology and computational neuroscience is understanding the interaction between extrinsic signals from feedforward connections and intracortical signals from lateral connections. We propose here a computational model for motion perception based on the assumption that the local cortical circuits in the medio-temporal area (area MT) implement a Bayesian inference principle. This approach establishes a functional balance between feedforward and lateral, excitatory and inhibitory, inputs. The model reproduces most of the known properties of the neurons in area MT in response to moving stimuli. It accounts for important motion perception phenomena including motion transparency, spatial and temporal integration/segmentation. While integrating several properties of previously proposed models, it makes specific testable predictions concerning, in particular, temporal properties of neurons and the architecture of lateral connections in area MT. In addition, the proposed mechanism is consistent with the known properties of local cortical circuits in area V1. This suggests that Bayesian inference may be a general feature of information processing in cortical neuron populations.

Animals↗
PubMed2006

Perceptual interaction between real and synesthetic colors.

People with color-graphemic synesthesia experience vivid, reliable color upon viewing achromatic alphanumeric characters. Recent evidence indicates that synesthetic color experiences are as perceptually real as actual colors are for non-synesthetic observers. To investigate possible interactions between real and synesthetic colors, we tested two adult color-graphemic synesthetes on a pair of perceptual grouping tasks. In Experiment 1, we employed a well-known phenomenon of motion perception, bistable apparent motion, to explore whether synesthetic colors interact with real colors in grouping over time. Two-frame apparent motion sequences were presented with both path lengths and colors systematically manipulated. Results showed that synesthetic colors of motion tokens interacted with matching real colors of the corresponding motion tokens, which could subsequently bias perceived direction of motion. In Experiment 2, we exploited binocular rivalry, a condition under which two dissimilar monocular images compete with each other and result in perceptual switches, to explore whether synesthetic colors interact with real colors in grouping over space. Pairs of rival images with two different characters were presented dichoptically with colors of characters manipulated. Results showed that synesthetic and real colors of characters tended to group together, which, in turn, promoted the perceived global dominance during binocular rivalry. Therefore, the present results identify substantial interaction between synesthetic colors and real colors in perceptual grouping.

Adult↗
PubMed2002

An oscillatory correlation model of visual motion analysis.

We describe and evaluate a model of motion perception based on the integration of information from two parallel pathways: a motion pathway and a luminance pathway. The motion pathway has two stages. The first stage measures and pools local motion across the input animation sequence and assigns reliability indices to these pooled measurements. The second stage groups locations on the basis of these measurements. In the luminance pathway, the input scene is segmented into regions on the basis of similarities in luminance. In a subsequent integration stage, motion and luminance segments are combined to obtain the final estimates of object motion. The neural network architecture we employ is based on LEGION (locally excitatory globally inhibitory oscillator networks), a scheme for feature binding and region labeling based on oscillatory correlation. Many aspects of the model are implemented at the neural network level, whereas others are implemented at a more abstract level. We apply this model to the computation of moving, uniformly illuminated, two-dimensional surfaces that are either opaque or transparent. Model performance replicates a number of distinctive features of human motion perception.

Humans↗
PubMed1986

The role of visual pattern persistence in bistable stroboscopic motion.

Two alternating frames, each consisting of three square elements, were used to study bistable stroboscopic motion percepts. Bistable percepts were obtained which depend on the interstimulus interval (ISI) between the alternating frames. At short ISIs only end-to-end element motion was observed; and at higher ISIs only group motion was perceived. It was found that the progressive ISI-dependent transitions from element to group motion depended on element size and frame duration. These dependencies are predictable from the systematic influence which these variables are known also to exert on visual pattern persistence, indicating that such persistence contributes to determining which precept dominates during bistable stroboscopic motion sequences. These findings bear relevantly on recent attempts to conceptually relate bistable motion percepts to short-range stroboscopic motion processes.

Form Perception↗