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PubMed1998

Deficits and recovery of first- and second-order motion perception in patients with unilateral cortical lesions.

Unilateral lesions in the posterior parietal cortex can degrade motion perception in the contralesional visual hemifield. Our aim was to investigate whether deficits caused by cortical lesions may be different for first- and second-order motion perception, and to study the time scale of any potential recovery. In nine patients with circumscribed lesions mainly in the parietal and fronto-parietal cortex, thresholds for direction discrimination were measured for stimuli presented peripherally in their ipsi- and contralesional hemifield. Subjects had to identify the direction of a vertically moving object embedded in a background of dynamic random dot noise. The object consisted of various proportions of signal and noise dots. Signal dots were either (a) coherently moving in the same direction as the object (first-order), (b) stationary (second-order: drift-balanced), or (c) coherently moving in the opposite direction (second-order: theta). Noise dots were flickering. Two patients showed significant threshold elevations for all three types of motion stimuli presented in their contralesional hemifield, while thresholds for ipsilesional targets were unaffected. Neither showed any selective deficit of first- versus second-order motion perception, but second-order motion was more impaired. Their lesions probably included the motion area V5-MT, which was spared in the other seven patients. One of the patients, who was retested several times during a 27-month postlesional period, showed complete recovery for first- and second-order motion direction discrimination, as well as for the detection of speed differences.

Adult↗
PubMed1989

Some additional predictions and further tests of the Marr-Ullman model of motion perception.

The Marr-Ullman model for motion detection in the human visual system functions by means of the dual input of polarity-specific edge detectors and luminance change detectors. Moulden and Begg (1986) found a polarity-specific motion aftereffect which they claimed provided support for this dual input model. The logic of their experiment is examined, and it is shown that several additional predictions arise from the Marr-Ullman model, which were not supported by Moulden and Begg's study. A more powerful experiment was carried out and these additional predictions were disconfirmed, although the polarity-specific effect did emerge. A consideration of alternative explanations of this effect led to a second experiment in which an attempt was made to discover the actual determinants of the effect. This revealed that polarity-specific units are unlikely to play any part in the phenomenon. It was concluded, in the light of this and other evidence, that one of a class of alternative models is more likely to be the actual mechanism for motion perception. However, careful consideration of the Marr-Ullman model indicated that it may be untestable in principle if various differentially weighted levels of neural integration are envisaged.

Attention↗
PubMed1995

Motion perception deficits from midline cerebellar lesions in human.

Although visual motion processing is commonly thought to be mediated solely by visual cortical areas, this human lesion study suggests that the cerebellum also has a role. We found motion direction discrimination deficits in a group of patients with acute midline cerebellar lesions. Unlike normals and patients with hemispheric cerebellar lesions, these patients with midline lesions were unable to discern a global motion vector in a local stochastic motion display. This resembles the perceptual defect reported following cortical area MT lesions in primates. This motion perception deficit may result from damage to a cerebellar mechanism involved in perceptual stabilization. Disruption of this comparator mechanism is sufficient to produce a severe motion perception deficit even though cortical visual processing mechanisms are still intact.

Adult↗
PubMed1990

[An experiment on the theory of visual motion perception].

Two classes of theories of motion perception were studied: correlation and gradient models (in the sense of D. Marr). Random-dot kinematograms with a shifted square were presented to subjects, and the 80% threshold for detection of correct direction of movement was determined. Correlation models predict scale invariance, that is, a constant shift measured in units of texture elements of the translated pattern in spite of a geometric magnification. This was refuted for all subjects. The increase of the recognizable translation with the area of the translated form was verified except for the patterns with the largest texture elements (8 minutes of arc). This prediction, however, is not very specific for competing theories. Gradient models are not yet fully specified, and they contain some free parameters. They cannot be tested strictly, but there exist reasonable numerical parameter values by which our data can be satisfactorily explained.

Adult↗
PubMed1986

Object-motion detection affected by concurrent self-motion perception: psychophysics of a new phenomenon.

Thresholds for object-motion detection are significantly raised when concurrent self-motion perception is induced by either vestibular, or visual, or cervico-somatosensory stimulation. Active sinusoidal horizontal head oscillations with compensatory vestibulo-ocular reflex (VOR) and foveal or eccentrical target presentation; 'passive' head movements with fixation suppression of the VOR; pure body oscillations with the head fixed in space (cervical stimulation); optokinetically induced apparent self-motion (circularvection). This new visual phenomenon of a physiological 'inhibitory interaction' between object- and self-motion perception seems to have a somatosensory motor analogue. It may reflect the disadventageous side effect due to unspecificness of an otherwise beneficial space constancy mechanism, which provides us with the image of a stable world during locomotion.

Adolescent↗
PubMed1989

Monocular motion sensing, binocular motion perception.

The two-process account of motion perception and its binocular organization were addressed in experiments on apparent movement (AM) with three types of grating: sinusoidal; random bar width; and square-wave with missing fundamental (MF). Monocular MF gratings sampled four times per cycle of drift always appeared to move backwards. Here AM was unrelated to the spatial appearance of the pattern, and followed the motion of the dominant spatial frequency component (the third harmonic). We take this reversed AM to be characteristic of "short-range" motion sensors. It did not occur dichoptically, implying that the direction-selective mechanism of motion sensors is purely monocular. AM was seen with dichoptic presentation for all three types of grating. Performance improved with the length of the stimulus sequence, as predicted by probability summation. This result reconciles previous positive and negative findings on dichoptic AM. The perceived direction of dichoptic AM was consistent with polarity-selective matching of features over time (the "long-range process"). The most telling effect supporting feature-matching in dichoptic motion was that dichoptic MF motion reversed direction with a change in the visible features of the pattern (induced by changes in contrast and pulse duration); monocular apparent motion did not. Two routes from spatial frequency channels to the perception of object motion are discussed.

Contrast Sensitivity↗
PubMed2000

Attention mechanisms for multi-location first- and second-order motion perception.

We applied the external noise plus attention paradigm to study attention mechanisms involved in concurrent first-order and second-order motion perception at two spatial locations. Cued to attend to one of the locations, the observer was instructed to independently judge direction of motion of either first-order (Experiment 1) or second-order (Experiment 2) motion stimuli at both locations in every trial. Across trials, systematically controlled amounts of external noise were added to the motion displays. We measured motion threshold at three performance criteria in every attention x external noise condition. We find that observers could, without any loss, simultaneously compute first-order motion direction at two widely separated spatial locations across a broad range of external noise conditions. However, considerable loss occurred at the unattended location in processing second-order motion direction at two separated spatial locations. We conclude that, under the conditions investigated in the current study, (1) in first-order motion perception, the visual system could simultaneously process motion direction at two widely separated locations without any capacity limitation; (2) in second-order motion perception, attending to a spatial location enhances stimulus contrast at that location by a factor of about 1.37 (or equivalently, reduces the internal additive noise by a factor of about 0.73).

Attention↗
PubMed1992

Absence of smooth motion perception in color vision.

We have tested the behavioral evidence for a separation of the processing of color contrast from motion in the human visual system. Two different aspects of motion perception are examined; the identification of the direction of movement of a chromatic grating and the perception of smooth motion. The results show that color vision is at no great disadvantage in the identification of direction of movement, since this can be done at color contrasts quite close to detection threshold over a wide range of spatial and temporal frequencies. However, we find that subjects can identify direction without having the genuine perception of smooth motion. Smooth motion perception is revealed to be highly impaired since it is detected only at very high color contrasts and over a narrow range of spatial temporal conditions.

Color Perception↗
PubMed1997

Second-order motion perception in peripheral vision: limits of early filtering.

Spatial and temporal analysis of contrast-modulated sine-wave gratings reveals that the second-order motion stimulus contains two sidebands, with equal energy but moving in opposite directions, flanking a stationary carrier. Any early linear spatial filtering process in the visual system that attenuates one sideband more than the other will be detrimental to the balance between the two sidebands, so that the perceived direction of the carrier might be opposite to that of the envelope motion. We tested this hypothesis by using contrast-modulated gratings presented centrally or at 20 deg in the horizontal nasal field with a two-alternative forced-choice staircase paradigm. We found that when the envelope frequency was close to that of the carrier, a second-order stimulus whose envelope motion direction was correctly identified in the fovea appeared to drift in the opposite direction in the periphery. Further increasing the envelope spatial frequency resulted in a reversed motion percept in both central and peripheral viewing conditions. For subjects to identify correctly the direction of motion of the envelope, the spatial frequency ratio of the carrier to the envelope had to be more than 2 in the fovea and more than 6 in the periphery. These phenomena in second-order motion perception can be explained by a linear model of motion detection with an early spatial filtering process. Further experiments and computer simulation show that undersampling of the carrier has little effect on second-order motion perception in the periphery, as long as the carrier is detectable.

Adult↗
PubMed1995

The consequences of inactivating areas V1 and V5 on visual motion perception.

We studied the capacity of normal humans to discriminate the direction of motion of visual stimuli when areas V1 or V5 were reversibly inactivated with transcranial magnetic stimulation. We found that (i) magnetic stimulation of V5 at intervals of -20 to +10 ms before or after the onset of visual stimulation was effective in abolishing motion perception--other delays were not; (ii) magnetic stimulation of V1 abolished motion perception only marginally and at delays which were significantly different from those obtained with V5, the stimulation now being effective only at delays of 60-70 ms after the onset of visual stimulation. We conclude (i) that stimulation of V5 is a much more potent way of inducing akinetopsia (motion imperception) than stimulation of V1; (ii) that perceptually effective visual motion signals reach V5 at or before 30 ms and reach V1 at or before 60 ms--consequently, perceptually effective motion signals reach V5 before they reach V1; (iii) that, given the time course of arrival of signals in V1 and V5, it takes about 30-50 ms for signals from V1 to reach V5. We conclude further that there are probably two components reaching V5 from the retina, a fast one which bypasses V1 and a slow one which reaches it through V1.

Brain Mapping↗
PubMed1998

Anisotropies in visual motion perception: a fresh look.

We measured motion-detection and motion-discrimination performance for different directions of motion, using stochastic motion sequences. Random-dot cinematograms containing 200 dots in a circular aperture were used as stimuli in a two-interval forced-choice procedure. In the motion-detection experiment, observers judged which of two intervals contained weak coherent motion, the other internal containing random motion only. In the direction-discrimination experiment, observers viewed a standard direction of motion followed by comparison motion in a slightly different direction. Observers indicated whether the comparison was clockwise or counterclockwise, relative to the standard. Twelve directions of motion were tested in the detection task and five standard directions (three cardinal directions and two oblique directions) in the discrimination task. Detection thresholds were invariant with direction of motion, but direction-discrimination thresholds were significantly higher for motion in oblique directions, even at low-coherence levels. Results from control conditions ruled out monitor artifacts and indicate that the oblique effect is relative to retinal coordinates. These results have broad implications for computational and physiological models of motion perception.

Anisotropy↗
PubMed1997

Visually induced motion perception and visual control of postural sway in congenital nystagmus.

In congenital nystagmus (CN) the threshold for detecting motion of visual objects is increased. To determine whether this increase is due to a deterioration of visual motion signals or whether visual-vestibular interactions (which are necessary to judge object-motion in space) are also involved we examined how CN patients use visual motion signals to evaluate self-motion in perceptual and behavioral tasks. Using an optokinetic drum we measured the minimum optokinetic acceleration necessary to induced motion perception of the visual environment in CN patients. This threshold was significantly elevated in the CN patients compared with normals (20.1 deg/s2 to 3.25 deg/s2). We further addressed the question whether the elevation of this threshold is due to a deficiency in evaluating visual motion in general or to a specific modification affecting the percept of visual object-motion with respect to the inertial reference only. We thus measured the latency of visually induced self-motion perception, which was found to be very similar or even slightly smaller (1.7 +/- 0.7 s) compared with normals (2.2 +/- 1.7 s). Moreover, subjects with CN were found to use vision quite efficiently for the visual stabilization of posture (Romberg quotient 2.0 +/- 1.16), even if they did not reach the level of normals (Romberg quotient 3.7 +/- 1.1). The results indicate that CN affects the estimate of object-motion in a specific and much more severe way than the estimate of self-motion. The minimal effect of CN on self-motion perception can be explained by the low pass characteristics of the optokinetic input to self-motion perception. The specific deficiency in detecting object-motion indicates that adaptation to CN occurs on the level of visual--vestibular interactions for the perception of visual object-motion and not on the level of visual motion signals.

Adolescent↗
PubMed1996

Biases of motion perception revealed by reversing gratings in humans who had infantile-onset strabismus.

Motion perception was tested by requiring adult subjects to view gratings that remained stationary but reversed in contrast several times per second. Subjects viewed monocularly and judged whether the gratings were stationary, or moving in one direction, in successive 3s trials. Subjects who had early-onset strabismus most frequently perceived vertically oriented gratings to be moving nasalward, and horizontally oriented gratings to be moving up or down. Normal subjects and subjects who had late-onset strabismus most frequently perceived the gratings to be stationary. The asymmetries of motion perception in early-onset strabismus imply that the visual motion neurons of cerebral cortex develop properly only if they receive normal binocular input during infancy.

Adolescent↗
PubMed1994

Psychophysical evidence of differential latencies of colour inputs to motion perception.

A novel psychophysical observation allows the determination of the relative latencies with which long, middle, and short cone signals provide input to motion perception. It is known that when two spatially displaced isoluminant stimuli in spectrally different colours are simultaneously presented, any temporal lag between the perception of the two will, due to the spatial displacement, cause the perception of apparent motion. The illusion reported here occurs through the inadvertent production of spatial displacement; peripheral observation of the boundary between two differently-coloured neighbouring areas which alternately interchange colours leads, due to transverse chromatic aberration caused by the eye's optics, to the formation of a double boundary on the retina, the serial perceptions of which create the sensation of motion. By offsetting the relative temporal phases of any two colours we have determined the relative magnitude of the latencies with which they provide input to motion perception. In all subjects motion of blue is perceived after that of red, and green is perceived after that of blue. The origins of these latencies are unclear.

Color Perception↗
PubMed2000

Orientation specificity in biological motion perception.

We addressed the issue of how display orientation affects the perception of biological motion. In Experiment 1, spontaneous recognition of a point-light walker improved abruptly with image-plane display rotation from inverted to upright orientation. Within a range of orientations from 180 degrees to 90 degrees, it was dramatically impeded. Using ROC analysis, we showed (Experiments 2 and 3) that despite prior familiarization with a point-light figure at all orientations, its detectability within a mask decreased with a change in orientation from upright to a range of 90 degrees-180 degrees. In Experiment 4, a priming effect in biological motion was observed only if a prime corresponded to a range of deviations from upright orientation within which the display was spontaneously recognizable. The findings indicate that display orientation nonmonotonically affects the perception of biological motion. Moreover, top-down influence on the perception of biological motion is limited by display orientation.

Adolescent↗
PubMed1992

Motion perception and aging.

The authors used a correlated motion paradigm to investigate the effects of aging and gender on motion sensitivity. In 2 experiments with a total of 50 elderly and 50 young subjects, motion thresholds were significantly higher for elderly women. The correlated motion signal, which was embedded in random motion, may have been coherent to subjects in much the same way a form is in Witkin's Embedded Figures Test (EFT). In Experiment 2, EFT scores were obtained. A significant positive relationship between motion thresholds and EFT performance was found within each age group. Although gender-related perceptual style differences may contribute to motion perception effects, the authors argue that a common neural factor contributes to performance on both the EFT and the correlated motion task.

Adult↗
PubMed1990

Intact "biological motion" and "structure from motion" perception in a patient with impaired motion mechanisms: a case study.

A series of psychophysical tests examining early and later aspects of image-motion processing were conducted in a patient with bilateral lesions involving the posterior visual pathways, affecting the lateral parietal-temporal-occipital cortex and the underlying white matter (as shown by magnetic resonance imaging studies and confirmed by neuro-ophthalmological and neuropsychological examinations). Visual acuity, form discrimination, color, and contrast-sensitivity discrimination were normal whereas spatial localization, line bisection, depth, and binocular stereopsis were severely impaired. Performance on early motion tasks was very poor. These include seeing coherent motion in random noise (Newsome & Paré, 1988), speed discrimination, and seeing two-dimensional form from relative speed of motion. However, on higher-order motion tasks the patient was able to identify actions from the evolving pattern of dots placed at the joints of a human actor (Johansson, 1973) as well as discriminating three-dimensional structure of a cylinder from motion in a dynamic random-dot field. The pattern of these results is at odds with the hypothesis that precise metrical comparison of early motion measurements is necessary for higher-order "structure from motion" tasks.

Cerebral Cortex↗
PubMed1993

Spatio-temporal characteristics of human motion perception.

A bi-local detector array model was assumed to describe the functional performance of monocular motion perception. Distributions of model parameters were measured in human vision at several positions in the visual field. The stimulus paradigm was designed to measure directional motion perception thresholds for individual combinations of spatial displacement and temporal delay in random dot apparent motion stimuli. The resulting data support previous results on perceivable spatial displacement limits in human vision but also indicate that both minimum and maximum perceivable spatial displacement thresholds in human observers have a similar dependence on temporal delay. This dependence changes with eccentricity in the visual field in a qualitatively similar manner but by quantitatively different factors. A description of possible biological properties of the bi-local detector population is presented that may explain how detection of spatio-temporal pattern displacements can be performed by a single system. Such a system also predicts that minimum and maximum perceivable spatial displacement thresholds should scale with visual field eccentricity in a manner consistent with our results.

Humans↗