The relative accuracy of visual perception of motion during fixation and pursuit.
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Ergonomics↗
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Is global motion really based on spatial integration of local motion signals?
Previous studies have shown that a random-dot kinematogram (RDK) comprising dots, each of which takes a random walk in direction or speed over time, can appear to flow in a single direction. This has been interpreted as evidence for the existence of a co-operative network linking neurons sensitive to different directions/speeds and different spatial locations. We have investigated the possibility that global motion perception in such patterns might simply reflect motion energy detection at a coarse spatial scale (such that many dots fall in the receptive field of one energy detector) without the need to encode local dot motions on a fine spatial scale and then integrate their motions over space. We created random-walk RDKs and then spatially high-pass filtered them to remove low spatial frequencies. Perception of global motion was unimpaired for both direction and speed random walks, showing that the phenomenon is not reliant on low spatial frequencies and must, therefore, involve integration of local motion signals across space, as originally postulated.
Discrimination, Psychological↗
Vagaries of visual perception in autism.
Three classes of perceptual phenomena have repeatedly been associated with autism spectrum disorder (ASD): superior processing of fine detail (local structure), either inferior processing of overall/global structure or an ability to ignore disruptive global/contextual information, and impaired motion perception. This review evaluates the quality of the evidence bearing on these three phenomena. We argue that while superior local processing has been robustly demonstrated, conclusions about global processing cannot be definitively drawn from the experiments to date, which have generally not precluded observers using more local cues. Perception of moving stimuli is impaired in ASD, but explanations in terms of magnocellular/dorsal deficits do not appear to be sufficient. We suggest that abnormalities in the superior temporal sulcus (STS) may provide a neural basis for the range of motion-processing deficits observed in ASD, including biological motion perception. Such an explanation may also provide a link between perceptual abnormalities and specific deficits in social cognition associated with autism.
Autistic Disorder↗
Optokinetic eye movements elicited by an apparently moving visual pattern in guinea pigs.
Based on known anatomical and physiological properties, guinea pigs could be expected to show a lack of cortical impact on the basic properties of optokinetic nystagmus (OKN) such as eye movements elicited by a rotating striped drum. The present study aimed to clarify the question of whether the guinea pig's brainstem-mediated circuit is capable of generating horizontal OKN with the animal binocularly viewing a stationary stroboscopically illuminated striped pattern (apparent-motion OKN). A striped drum with a pattern periodicity of 2.37 degrees was rotated around the animal. The OKN buildup under real stimulation conditions was found to be largely devoid of a rapid initial rise in slow-phase eye velocity (direct OKN component). Only in a few recordings was a slight initially faster acceleration seen eliciting slow-phase eye velocities of 2 degrees/s at the most. The lack of a rapid initial rise proves that the optokinetic reflex loop does not possess a functionally significant cortically mediated component. To achieve apparent-motion OKN, initially in each recording real-motion OKN was elicited by the constantly illuminated rotating pattern. Then, 60 or 90 s later the drum was stopped and the illumination switched over from constant to flashing light. Following Grüsser and Behrens (1979), we calculated an apparent stimulus velocity (= flash frequency x 2.37 degrees) and an apparent OKN gain. We found that all animals continued in nystagmus under the flashing light condition. The slow-phase eye velocity was the same as under real pattern motion, with gain values of between 0.36 and 0.7. In two animals we produced an apparent gain close to unity by suddenly doubling the flash interval, i.e., halving the apparent drum velocity. This gain, however, did not remain at a high level: The slow-phase eye velocity decreased until the previous lower gain was reached again. The data indicate that cortical mechanisms are not necessary to produce nystagmus under apparent-motion stimulation and neither phi nor sigma phenomena of motion perception satisfactorily explain the apparent-motion OKN in the guinea pig. Our data provide evidence that the brainstem-located velocity storage mechanism plays a decisive role in keeping the eye in motion under apparent-motion stimulation.
Animals↗
Segmentation versus integration in visual motion processing.
Reliable motion perception requires processes that integrate visual motion signals from neighbouring locations in the visual field, which should have the effect of smoothing out spatial variations in velocity. However, we also require motion processing to be very sensitive to local velocity differences, so that moving objects appear sharply distinct from their background and specific differential properties of optic flow associated with the observer's motion can be detected. Perceptual experiments give evidence both for integrative processes, which lead to spreading of perceived motion, and for differential processes, which lead to motion contrast and segmentation. Current and future experiments might allow tests of theoretical schemes that employ adaptive networks and/or multiple representations in order to reconcile the conflicting demands of integration and segmentation.
Animals↗
No direction-specific bimodal facilitation for audiovisual motion detection.
After several decades of unimodal perceptual research, interest is turning increasingly to cross-modal interactions. At a physiological level, the existence of bimodal cells is well documented and it is known that correlated audiovisual input enhances localisation and orienting behaviours. Audiovisual perceptual interactions have also been demonstrated (e.g., the well-known McGurk effect). The present study explores motion perception and asks whether correlated audiovisual motion signals would be better detected than unimodal motions or bimodal motions in opposing directions. Using a dynamic random-dot field with variable motion coherence as a visual stimulus, together with an auditory motion defined by a stereo noise source smoothly translating along a horizontal trajectory, we find that correlated bimodal motion yields only a slight improvement (approximately a square root of two advantage) in detection threshold relative to unimodal detection. The size of this benefit is consistent with a statistical advantage rather than a bimodal facilitation account. Moreover, anticorrelated bimodal motion showed the same modest improvement, again speaking against linear summation but consistent with statistical combination of visual and auditory signals. These findings were replicated in peripheral as well as in central vision, and with translating visual objects as well as with spatially distributed visual motion. The superadditivity observed neurally (especially in deep-layer superior collicular cells), when weak unimodal signals are combined in bimodal cells does not apply to the detection of linear translational motion.
Acoustic Stimulation↗
The Leaning Tower of Pisa effect: an illusion mediated by colour, brightness, and motion.
We report a novel, easily observed, and extraordinarily striking optical illusion mediated by interactions of colour, brightness, form, and motion perception--the Leaning Tower of Pisa (LTOP) illusion. Under some circumstances, the perception of orientation of coloured forms is radically altered by rotary movement. We demonstrate that this kinetic effect--easily reproduced with a common record turntable--is optimised by particular colour and brightness differences between foreground and background with an illusory tilt of 8 degrees and more. The described illusions can be easily studied at home by downloading the colour figures from www.perceptionweb.com/perc1000/ditzinger, printing them on a common colour printer and placing them on a rotating record turntable.
Color Perception↗
Texture segregation by chromatic and achromatic visual pathways: an analogy with motion processing.
We present results to show that texture segregation can be obtained through the so-called coherent spatial grouping of local shape (orientation) and of local color under both nonequiluminant and equiluminant conditions. Color grouping entails texture segregation independent of orientation grouping, while the reverse is not true under equiluminant conditions. The experiments permit the isolation of chromatic- and luminance-oriented mechanisms, as well as of chromatic nonoriented mechanisms, all of which contribute to texture discrimination. As a general rule, the present results (including the asymmetry between color and orientation grouping) are similar to those obtained by us in a series of motion-perception experiments. This similarity suggests that the perceptual rules governing spatial grouping are analogous (if not identical) to those governing spatiotemporal grouping. As in the case of directional discrimination, texture-discrimination performances may be accounted for by the activation of higher-order units receiving inputs from subunits, all of which display similar tuning properties within a multidimensional space.
Color Perception↗
Observations on the adaptation of induced motion.
Induced motion (IM) was measured before and after a 10-min adaptation period during which subjects viewed the IM display without judging IM magnitude. The inducing stimulus was a rectangle, which contains both horizontal and vertical reference detail. The magnitude of IM was significantly lower following the adaptation period. This result is inconsistent with the hypothesis that adaptation of IM represents an instance of perceptual learning wherein the contribution of relative motion to motion perception is reduced. In a separate study, similar results were obtained when the inducing stimulus was a single vertical bar presented either to the left or to the right of the fixation stimulus. In addition, adaptation was obtained when the location of the inducing bar was changed during test measures, demonstrating that this effect is not specific to the retinal locus of the adaptation stimulus.
Adult↗
Computational modelling of optic flow selectivity in MSTd neurons.
In neurophysiological experiments examining the selectivity of MSTd neurons to visual motion components of optic flow stimuli in monkeys, Duffy and Wurtz (1991) reported cells with double-component (plano-radial and plano-circular) and triple-component (plano-radial-circular) selectivities, while Graziano et al (1994) reported neurons selective to a continuum of optic flow stimuli including spiral motion. Here, we address these reported findings under simulated experimental conditions by examining the development of optic flow selectivity in the hidden units of a two-layer back-propagation network. We also examine network motion sensitivity during simulated psychophysical tests via the addition of a competitive decision layer. Network analysis with neurophysiological stimuli identified a majority of hidden units whose position invariance and motion selectivity were consistent with MSTd responses to the visual motion components of optic flow stimuli reported by Duffy and Wurtz and Graziano et al. Furthermore, the hidden units developed a continuum of optic flow selectivities independent of the biases associated with the specification of the motion selectivity in the output layer. During psychophysical testing, network responses showed motion sensitivities which met or exceeded human performance. Within the limitations imposed by the learning algorithm, the psychophysical results were consistent with a model of global motion perception via local integration along complex motion trajectories.
Animals↗
[Energy-saving, effective and elegant. Awareness through motion. Body perception and relaxation technic, no. 2: Hightened self-awareness through bodily and spiritual training].
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Humans↗
Computer simulations of figure-ground discrimination in the visual system of the fly.
Figure-ground discrimination and pattern discrimination represent one of the most important problems in computer vision. Based on computational neuronal network model proposed by Reichardt et al. for figure-ground discrimination in the visual system of the fly, entire systematic computer simulations were carried out under nonstationary conditions. Results show that the model network and simulations have predictive power for behavioural experimental results. This paper proposes that motion perception and elementary pattern discrimination in human visual system may be mediated by some kind of figure-ground system with movement detectors as input layer.
Animals↗
On the similarities between the perception and production of elliptical trajectories.
In an earlier study, Viviani and Stucchi (J Exp Psychol Hum Percept Perform 18:603-623, 1992) have introduced a visual illusion, whereby it was shown that when subjects are asked to determine what movement of a light spot, when tracing an elliptical trajectory, appears to be most uniform, they tend to choose movements that are close to obeying the 2/3 power law (Lacquaniti et al. Acta Psychol 54:115-130, 1983) rather than constant speed movements, even though the actual changes in velocity could exceed 200%. Here we have extended the study of this illusion by directly testing the effect of the shape (eccentricity) and size (perimeter) of the elliptical trajectory, the duration of the tracing of the ellipse and the effect of fixation on the subjects' decision regarding movement uniformity. We found that the ellipse's eccentricity and tracing out speed of the elliptical trajectory significantly affect the subjects' decisions, although the effect of eccentricity seems to be stronger than that of speed. Our findings also indicated that fixation significantly affects the subject's decision for ellipses that are more eccentric. Surprisingly, the ellipse's perimeter had a much smaller effect on the subjects' decisions, although changes in the ellipse's perimeter should have the same effect on the average velocity as changes in the time it takes to trace out the ellipse. This suggested the possibility that the subjects based their decision regarding movement uniformity on other velocity variables in addition to tangential velocity. Computer simulations we have performed have led us to conclude that the subjects' perception of movement uniformity may also be based on assessing the variations in angular velocity and possibly also in affine velocity. Our behavioral and simulation studies thus suggest that the motion perception system is quite responsive to variations in the velocity along an elliptical trajectory but in a way that depends on the path's curvature. Furthermore, the movement is judged to be more uniform when there are minimal differences in angular, tangential and perhaps also in affine velocities, along the trajectory. Our results suggest the existence of similar underlying constraints that affect both the motion perception and production systems when the movements are associated with very large velocities or large changes in velocity along more curved portions of the trajectory. Our observations therefore provide further insight into the possibility that these constraints are either imposed by the underlying neuronal dynamics, the internal architecture of the cortical neural populations or the variables used in the coding of both sensory and motor information regarding movement.
Adolescent↗
Repetitive motion in perception of tactile sensation in the fingers of string players.
Little is known about the mechanisms that underlie the pathophysiology involved in the development of cumulative trauma disorders. Musicians, specifically string players, may be a useful model to examine the cumulative effects of repetitive motion given the highly attended movements of their left hands and the stereotypical grasp of their right hands. Musculoskeletal disorders related to playing are experienced by 39% to 87% of musicians, making musicians a potentially good model for the study of factors involved in development of cumulative trauma disorders. Sensory thresholds for two-point discrimination and light touch were measured in all phalanges of each digit, of each hand. Comparisons were made within and between a control group of 10 nonmusicians who did not engage in repetitive motion and 10 healthy musicians who did. There were 5 violinists, 2 violists, and 3 cellists. The Non-musician group perceived two-points and light touch at significantly lower thresholds in the proximal phalanges of the left hand than the right hand. Significant differences were not present between right and left hands for the means of distal, middle, and proximal phalanges of the Musician group. This lack of significant difference may be due to higher sensory thresholds associated with repetitive use of the left hand of the musicians.
Adult↗
Congruency effects between auditory and tactile motion: extending the phenomenon of cross-modal dynamic capture.
Behavioral studies of multisensory integration in motion perception have focused on the particular case of visual and auditory signals. Here, we addressed a new case: audition and touch. In Experiment 1, we tested the effects of an apparent motion stream presented in an irrelevant modality (audition or touch) on the perception of apparent motion streams in the other modality (touch or audition, respectively). We found significant congruency effects (lower performance when the direction of motion in the irrelevant modality was incongruent with the direction of the target) for the two possible modality combinations. This congruency effect was asymmetrical, with tactile motion distractors having a stronger influence on auditory motion perception than vice versa In Experiment 2, we used auditory motion targets and tactile motion distractors while participants adopted one of two possible postures: arms uncrossed or arms crossed. The effects of tactile motion on auditory motion judgments were replicated in the arms-uncrossed posture, but they dissipated in the arms-crossed posture. The implications of these results are discussed in light of current findings regarding the representation of tactile and auditory space.
Auditory Perception↗
Differential activation solution to the motion correspondence problem.
The correspondence problem arises in motion perception when more than one motion path is possible for discontinuously presented visual elements. Ullman's (1979) "minimal mapping" solution to the correspondence problem, for which costs are assigned to competing motion paths on the basis of element affinities (e.g., greater affinity for elements that are closer together), is distinguished from a solution based on the differential activation of directionally selective motion detectors. The differential activation account was supported by evidence that path length affects detector activation in a paradignm for which motion correspondence is not a factor. Effects on detector activation in this paradigm also were the basis for the successful prediction of path luminance effects on solutions to the motion correspondence problem. Finally, the differential activation account was distinguished from minimal mapping theory by an experiment showing that the perception of an element moving simultaneously in two directions does not depend on whether the two motions are matched in path-length determined affinity; it is sufficient that the activation of detectors responding to each of the two motion directions is above the threshold level required for the motions to be perceived. Implications of the differential activation solution are discussed for the stability of perceived motions once they are established, and the adaptation of perceived and unperceived motions.
Adult↗
Perception and production of biological movement in patients with early periventricular brain lesions.
Recent neuroimaging and psychophysical findings suggest that perception and production of human body motion share a common representational network. In the present study, we address the issue of whether early disorders in production of biological movement correspond to impairment in biological motion perception. By using the simultaneous masking paradigm, we examined visual sensitivity to biological motion in adolescents (aged 13-16 years) who were born very preterm (at 27-33 gestational weeks). In a confidence rating procedure, the presence of a point-light walking figure embedded in a moving mask was judged. The participants differed in their locomotion ability, ranging from normal to a complete walking disability exhibiting signs of leg-dominated bilateral spastic cerebral palsy (BS-CP) caused by periventricular leukomalacia (PVL). Irrespective of an ability to produce movement, patients with a similar extent of PVL in the parieto-occipital complex exhibit nearly the same sensitivity to biological motion. Sensitivity correlates negatively with the extent of PVL over the parieto-occipital complex, whereas neither the severity of motor disorder nor the severity of pyramidal tract affection relate significantly to the sensitivity index. The data suggest that perception of biological motion is not substantially affected by an observer's early restrictions in body movement. Instead, the findings favour the assumption that the common network for perception and production of biological motion might be inherent for the brain. Motor experience per se does not appear to be necessary for the visual analysis of human movement.
Adolescent↗
[Effects of the peripheral vision on visually induced vertigo].
Visually induced vertigo, or motion sickness, is thought to be mainly influenced by motion perception, not by shape perception. We examined this point by comparing the effect of the foveal vision on the visually induced vertigo with that of the peripheral vision. We set up three kinds of display conditions: Foveal vision (F), peripheral vision (P), and foveal + peripheral vision (F + P). Videotaped motion was presented on the display. The results showed that a drifting eye movement was larger after the experiment than before the experiment in the (P) and the (F + P) conditions, but not in the (F) condition. In addition, the mirror drawing was improved only in the (F) condition. Subjective ratings for the vertigo were higher in both the (P) and the (F + P) conditions than in the (F) condition. These results indicate that some visual units concerning low spatial frequencies participate in the visually induced vertigo.
Adult↗