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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↗
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↗
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↗
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↗
PubMed1991

Does primate motion perception depend on the magnocellular pathway?

This study examined the importance of the primate magnocellular retinocortical pathway in the perception of moving stimuli. A portion of the magnocellular pathway was permanently and selectively interrupted by ibotenic acid injections in the LGN of macaque monkeys. We then tested contrast sensitivity for detecting moving stimuli, as well as two indices of motion perception, contrast sensitivity for opposite direction discrimination and speed difference thresholds, in the affected portion of the visual field. Magnocellular lesions greatly reduced detection contrast sensitivity at high temporal and low spatial frequencies and had a similar effect on contrast sensitivity for opposite direction discrimination under these same stimulus conditions. Consequently, opposite direction discriminations could be made at contrast threshold, suggesting that magnocellular lesions reduced the visibility of stimuli used to test direction perception, but did not act directly on direction perception. Magnocellular lesions also elevated speed difference thresholds under some stimulus conditions. However, this deficit was reduced or eliminated by raising the contrast of the test stimulus. Together, these findings suggest that magnocellular lesions reduce the visibility of stimuli used to test motion perception but that they do not appear to alter motion perception otherwise.

Animals↗
PubMed1990

Assimilation and contrast in motion perception: explorations in cooperativity.

Motions within one region of the field influence motion seen elsewhere. To explore this phenomenon we used cinematograms comprised of alternating strips within which dots (i) tended to move in one direction, or (ii) moved in random directions (dynamic noise). When alternating strips were narrow, motion in one direction induced a similar direction of illusory motion in the adjoining dynamic noise (assimilation); when alternating strips were wide, motion tended to induce an illusory opposed motion in the dynamic noise (contrast). Since this illusory motion exhibits hysteresis, it probably results from spatially distributed, cooperative processes. The shift from assimilation to contrast, as the cinematogram's strips increase in size, suggests that facilitatory and inhibitory influences of the network extend over different distances.

Contrast Sensitivity↗
PubMed1990

Consequences of spatial sampling for human motion perception.

This paper describes evidence for spatial aliasing in human motion perception. For a certain range of spatial frequencies, interference fringes drifting across the extrafoveal retina resemble two-dimensional spatial noise drifting in the opposite direction. For retinal locations within 10 deg of the fovea, the perceived direction of motion is veridical up to spatial frequencies near the cone Nyquist frequency, reverses between one and two times the cone Nyquist frequency, and sometimes reverses back to the correct direction at still higher frequencies. Thus two "motion nulls", or spatial frequencies at which the direction of motion is ambiguous, are typically observed at each retinal eccentricity. A computational model is described in which sinusoidal gratings are sampled by a cone mosaic and the direction of motion of the filtered output is computed. The model predicts that the second motion null, but not the first, should be relatively immune to postreceptoral processing and should roughly equal twice the cone Nyquist frequency. This prediction is confirmed by psychophysical experiments, providing a new technique to estimate cone spacing in the living human eye.

Discrimination, Psychological↗
PubMedDate not supplied

A comparison of the latencies of visually induced postural change and self-motion perception.

This study compared the latencies of visually induced postural change and self-motion perception under identical visual conditions. The results showed that a visual roll stimulus elicits postural tilt in the direction of scene motion and an increase in postural instability several seconds before the subject begins to perceive illusory self-motion (vection) in the opposite direction. Postural and vection latencies correlate highly with one another, but bear little relationship with the magnitude of either sway or vection.

Adolescent↗
PubMed1992

Interaction of vestibular and proprioceptive inputs for human self-motion perception.

Human perception of horizontal self(body)-motion in space was studied during various combinations of vestibular and leg-proprioceptive stimuli in the dark. During sinusoidal rotations of the trunk relative to the stationary feet (functionally synergistic combination) the perception was almost veridical over the frequency range tested (0.025-0.4 Hz). This finding suggested a dominance of the proprioceptive over the vestibular input, since the quantitative aspects of the perception (gain, phase, and detection threshold): (a) closely resembled those of the proprioceptive foot-to-trunk perception, and (b) clearly differed from those of the vestibular self-motion perception. However, when using other combinations, the self-motion perception changed in a monotonous way as a function of the two inputs, indicating that the two inputs do interact in a linear way. In a model of these findings the interaction occurs in two stages: (1) summation of a vestibular trunk-in-space signal and a (dynamically matched) proprioceptive foot-to-trunk signal yields an internal representation of foot support motion in space; (2) superposition of the latter by an almost ideal proprioceptive trunk-to-foot signal results in a representation of trunk-in-space motion (essentially proprioception-dependent and ideal when the feet are stationary).

Foot↗
PubMed1992

Computational aspects of motion perception in natural and artificial vision systems.

In this paper a computational scheme for motion perception in artificial and natural vision systems is described. The scheme is motivated by a mathematical analysis in which first-order spatial properties of optical flow, such as singular points and elementary components of optical flow, are shown to be salient features for the computation and analysis of visual motion. The fact that different methods for the computation of optical flow produce similar results is explained in terms of the simple spatial structure of the image motion of rigid bodies. Singular points and elementary flow components are used to compute motion parameters, such as time-to-collision and angular velocity, and also to segment the visual field into areas which correspond to different motions. Then a number of biological implications are discussed. Electrophysiological findings suggest that the brain perceives visual motion by detecting and analysing optical flow components. However, the cortical neurons, which seem to detect elementary flow components, are not able to extract these components from more complex flows. A simple model for the organization of the receptive field of these cells, which is consistent with anatomical and electrophysiological data, is described at the end of the paper.

Artificial Intelligence↗
PubMed1992

Insect motion perception.

The first step in this work of reconstruction of a theory of insect vision was to demonstrate that visual behaviour relies on scanning by self-motion and apparently involves measurement of angular velocities of contrasts moving across the eye. The next step was to demonstrate that parallax is also significant as a way of segmenting the visual scene into separate objects. There followed a series of experiments to rule out the existing theory that motion perception depends on autocorrelation, and at the same time an alternative theory was developed. The new theory assumes that at the level of the optic medulla there are numerous parallel channels on each visual axis, representing different neurons, all looking out for their specific combination of signals. The combinations are formed by positive, negative or no-change temporal contrasts at two adjacent visual axes at two successive times, forming 3(4) = 81 possible templates. Simulation of this highly parallel system shows that it can represent the moving image in a compact form that would be adequate to explain what is known for motion and form vision (but not colour vision) in insects. Form, like colour, would be seen as the ratio of numbers of responses of particular templates, in the same way that colours are seen as ratios of responses of receptors for different wavelengths.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1991

Visual motion perception from stimulation of the human medial parieto-occipital cortex.

Visual phenomena evoked by direct electrical stimulation of extrastriate cortex were observed in 30 epileptic patients as part of a presurgical investigation. An incremental sequence of low-level bipolar stimulation trains was delivered at medial and lateral pairs of contacts of stereotaxically-implanted multilead intracerebral electrodes in parietal, occipital and posterior temporal regions. Diffusion of stimulus afterdischarges was monitored by electrodes in temporal and frontal lobes and by the non-stimulated contacts of the stimulated electrode. Localized stimulations evoked few visual phenomena. The strongest anatomo-perceptual correlation was found for stimulation in the medial parieto-occipital fissure which evoked visual motion phenomena in all three patients stimulated in that region. The evoked motion perceptions were not associated with eye movements or any particular localization of the epileptic focus. These perceptions were only evoked once outside of the medial PO region at the 61 sites examined. The results suggest that the medial parieto-occipital region is closely linked to the human visual motion processing system.

Brain Mapping↗
PubMed1991

Two carriers for motion perception: color and luminance.

Starting with the experiments of Ramachandran and Gregory (Nature, 275, 55-56, 1978), several psychophysical studies in apparent motion (AM) have established that the perception of motion is significantly impaired at equiluminance. Still debated, however, is whether color alone can resolve ambiguities in AM. We report here on several psychophysical experiments, the quantitative results of which indicate that color does play a substantial role in AM. These findings seem to support recently proposed neurophysiological frameworks according to which there exist significant interactions among the neuronal pathways mediating the perception of basic visual attributes such as color, motion, form and depth.

Color Perception↗
PubMed1991

Using metamers to explore motion perception.

We examined conditions under which two quite different types of random-dot cinematograms were perceptually matched. In one stimulus type, directions of motion were defined by a uniform distribution; in the other, directions were drawn from a discrete set of just a few, widely separated directions. Cinematograms whose range of uniformly distributed directions lay between 180 and 270 deg could be matched by cinematograms containing just 6-10 discrete directions. The number of discrete directions required for a match was a nonmonotonic function of the range of directions present in the other cinematogram. The results are consistent with a line-element model in which the outputs of 12 direction-selective mechanisms, each with a half-amplitude half-bandwidth of 30 deg, are combined nonlinearly to produce the percept of motion.

Humans↗
PubMed1992

Attention-based motion perception.

Two "attentive" tracking tasks reveal the existence of an attention-based motion process. In the first task, oppositely rotating luminance and color gratings were superimposed. Because of masking from the color grating, the bars of the luminance grating were not visible; nevertheless, their motion was visible and it determined the perceived direction of the stimulus rotation. On the other hand, the bars of the color grating were visible but they could only be seen to move (in the opposite direction to the overall stimulus rotation) when they were tracked with attention. In a second task, the perceived velocity of a color grating, typically slow at equiluminance, speeded up when individual bars were attentively tracked. These findings demonstrate two independent motion processes: one that is "low-level" or automatic in that it signals motion even in the absence of attention to the stimulus, and one that is mediated by attention to visible features and provides accurate velocity judgments independently of the features being tracked.

Attention↗
PubMed1990

Transparency and coherence in human motion perception.

When confronted with moving images, the visual system often must decide whether the motion signals arise from a single object or from multiple objects. A special case of this problem arises when two independently moving gratings are superimposed. The gratings tend to cohere and move unambiguously in a single direction (pattern motion) instead of moving independently (component motion). Here we report that the tendency to see pattern motion depends very strongly on the luminance of the intersections (that is, to regions where the gratings overlap) relative to that of the gratings in a way that closely parallels the physics of transparency. When the luminance of these regions is chosen appropriately, pattern motion is destroyed and replaced by the appearance of two transparent gratings moving independently. The observations imply that motion detecting mechanisms in the visual system must have access to tacit 'knowledge' of the physics of transparency and that this knowledge can be used to segment the scene into different objects. The same knowledge could, in principle, be used to avoid confusing shadows with real object boundaries.

Humans↗
PubMed1989

The effects of dichoptic and binocular viewing on bistable motion percepts.

Two competitive percepts are produced from a bistable stroboscopic motion display. In this display two frames, each containing three horizontally arrayed elements are presented alternately for several cycles. At short interstimulus intervals (ISIs) element or end-to-end motion responses are obtained when the two inner, spatially overlapping elements are seen as stationary and the third element moves back and forth from one end to the other end. Group motion responses are obtained at longer ISIs when the three elements are seen to move back and forth as a group. The dominance of these two percepts across ISIs was controlled by the manipulation of (1) element size, (2) frame duration, and (3) viewing conditions. Under both binocular and dichoptic viewing, element motion responses increase as element size and frame duration decrease. By maximizing pattern persistence substantial element motion responses were obtained dichoptically as well as binocularly. Instead of supporting the existence of two separate, low-level and high-level, motion systems, our data suggest that there is a single, high-level mechanism for motion whose output can be modulated by pattern persistence.

Afterimage↗