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PubMed2005

The perception of motion transparency: a signal-to-noise limit.

A number of studies were conducted to determine how many transparent motion signals observers could simultaneously perceive. It was found that that the limit was two. However, observers required a signal intensity of about 42% in order to perceive a bi-directional transparent stimulus. This signal level was about three times that required to detect a uni-directional motion signal, and higher than was physically possible to achieve in a tri-directional stimulus (in a stimulus in which the different transparent signals are defined only by direction). These results indicate that signal intensity plays an important role in establishing the transparency limit and, as a consequence, implicates the global-motion area (V5/MT) in this process.

Discrimination, Psychological↗
PubMed1996

A general model for the perception of space and motion.

The perception of space and motion involves successive transformations of signals with respect to different reference systems. The visual input is coded in terms of retinal coordinates. The retinocentric values from each eye require to be unified, and to be combined with signals for eye position and movement. This egocentric reference provides a signal for the angular size, motion, or orientation of the stimulus with respect to the observer. The egocentric signals are transformed to a coordinate system that is three-dimensional-the geocentric frame of reference. Further transformations can occur at earlier levels owing to patterncentric interactions within the visual field. When the geocentric signal corresponds to the physical dimensions of space and motion, this is referred to as perceptual constancy.

Acceleration↗
PubMed2005

Visual areas involved in the perception of human movement from dynamic form analysis.

The perception of biological motion combines the analysis of form and motion. However, patient observations by Vaina et al. and psychophysical experiments by Beintema and Lappe showed that humans could perceive human movements (a walker) without local image motion information. Here, we examine the specificity of brain regions responsive to a biological motion stimulus without local image motion, using functional magnetic resonance imaging. We used the stimulus from Beintema and Lappe and compared the brain activity with a point-light display that does contain local motion information and was often used in previous studies. Recent imaging studies have identified areas sensitive to biological motion in both the motion-processing and the form-processing pathways of the visual system. We find a similar neuronal network engaged in biological motion perception, but more strongly manifested in form-processing than in motion-processing areas, namely, fusiform-/occipital face area and extrastriate body area.

Adult↗
PubMed1994

Perception of motion in depth from luminous rotating spirals: directional asymmetries during and after rotation.

Motion aftereffect (MAE) following spiral rotation is often asymmetrical: centrifugal MAE exceeds centripetal MAE. Pronounced MAE asymmetry has been reported for conditions--especially with a minimal background pattern--promoting perception of motion in depth. Such conditions are predicted to elicit motion asymmetry during adaptation. In the present study observers viewed luminous spirals monocularly in the dark; they timed, and scaled for convincingness, motion in depth during and after rotation. Motion in depth during rotation was often almost continuous, but recession was more convincing than was approach. Approaching MAE lasted longer and was more convincing than was receding MAE: the duration difference was more pronounced than has been found in other MAE studies, corroborating the link between MAE asymmetry and motion in depth. A possible line of explanation resides in comparing spiral motion in depth with real motion in depth of objects: in particular, the rapid visual change and collision with the observer that characterises real approach of an object is lacking in spiral approach. Interspecies differences for 'looming' and MAE are discussed.

Adult↗
PubMed1990

Electrophysiological evidence for visual-vestibular interaction in man.

The aim of the experiments reported here was to confirm electrophysiologically the results of psychophysical experiments, which demonstrated that thresholds for object-motion detection are significantly raised during both concurrent active or passive sinusoidal head oscillations and during visually induced self-motion perception (circularvection, CV). This intersensory inhibition could now be demonstrated electrophysiologically by recording visual motion evoked potentials both during concurrent sinusoidal head oscillations and during visually induced apparent self-motion of the objectively stationary subject. Recordings of visual contrast reversal evoked potentials failed to reveal such an interaction. Perceptual phenomena with multisensory stimulation are well described in the literature. Berthoz et al. demonstrated the dominant influence of the visual channel on vestibular thresholds such that the detection of a suprathreshold vestibular stimulation was clearly impaired by a simultaneously moving visual pattern inducing linearvection and vice versa. Comparable results are reported for circularvection. Evidence for inhibitory interaction between object-motion and simultaneous self-motion perception also exists. Electrophysiological data on intersensory interaction in humans have only been reported between electrical stimulation of a limb and its concurrent movement by means of scalp-recorded somatosensory-evoked potentials (SSEPs) (e.g. refs. 3, 5). Electrophysiological evidence for the interaction of visual object-motion and vestibular self-motion perception in humans has never been reported in the literature thus far, though Hood and Kayan demonstrated that retinal image motion makes a contribution to the vestibularly evoked bioelectric response.

Adult↗
PubMed1997

[Binocular functions in amblyopia and strabismus].

Regarding the changing trends in the concept, definition, etiological classification, and criteria for diagnosis of amblyopia, we reviewed a total of 4,693 cases of amblyopia seen during the past 37 years. The amblyopia was divided into four types: strabismic, anisometropic, ametropic, and form vision deprivative. There was a definite trend for the incidence to decrease and for the diagnosis to be made during earlier age in recent years. Although favorable recovery of visual acuity is obtained after treatment of amblyopia and strabismus, there are difficulties in obtaining good binocular functions in early-onset amblyopia and strabismus. This feature was evaluated in regard to motion perception asymmetry (MPA) and binocular depth from motion (DFM). Many cases of early-onset amblyopia and strabismus showed no disparity stereopsis, or position stereopsis, in spite of the presence of DFM. The MPA appeared to be closely related to early-onset esotropia regardless of age, while it disappeared and motion perception became symmetric 4 to 5 months after birth in normal infants. The DFM seemed to play an important role in maintaining good motor alignment for several years after surgery. I developed a checkerboard pattern stimulator in 1978. This method proved to be useful in developing binocular functions and motor alignment by applying simultaneous bifoveolar stimulation and anti-suppression. Extensive exposure to the stimulation was essential for therapeutic success.

Adolescent↗
PubMed2005

Perception of motion trajectory of object from the moving cast shadow in infants.

A moving cast shadow of the object affects the perception of the object's trajectory in adults [Kersten, D., Mamassian, P., & Knill, D. C. (1997). Moving cast shadow induce apparent motion in depth. Perception, 26, 171-192]. In the present study, we investigated by using a habituation-dishabituation procedure whether infants at 4- to 7-months old discriminate the motion trajectory of a ball from the moving shadow it casts. In Experiment 1, 4- to 5-month-old and 6- to 7-month-old were tested for ability to discriminate between a "depth" display containing a ball and a cast shadow with a diagonal trajectory and an "up" display containing a ball with a diagonal trajectory and a cast shadow with a horizontal trajectory. Six- and 7-month-old, but not 4- and 5-month-old, infants looked significantly longer at the "up" display than at the "depth" display. In Experiment 2, we tested whether 4- to 5-month-old and 6- to 7-month-old infants would perceive "up" motion as categorically different from "depth" depending on the object's 3-D trajectory. We used displays containing a ball and a cast shadow with the same trajectories as those in Experiment 1 except that the cast shadows appeared above the ball. These displays did not produce 3-D impressions in adults. Neither age group of infants exhibited significant differences between "up" and "depth" displays. When the results from the two experiments are considered, 6- and 7-month-old infants discriminated the motion trajectory of the ball from the moving cast shadows. This developmental emergence of depth perception from a moving cast shadow at 6 months of age is consistent with that of other pictorial depth cues.

Aging↗
PubMed1993

Complete interocular transfer of motion adaptation effects on motion coherence thresholds.

The binocularity of visual mechanisms in humans can be investigated by measuring the interocular transfer (IOT) of visual aftereffects. Cells in extrastriate visual areas of macaque, e.g. the middle temporal (MT) area, are uniformly binocular, whereas cells in striate area V1 vary in their degree of binocularity. Therefore, IOT of aftereffects mediated by extrastriate cortex should be nearly complete compared to the partial transfer (about 70%) found for aftereffects thought to be mediated by V1. If MT and other extrastriate areas play a significant role in motion perception, then IOT of motion adaptation aftereffects on the perception of moving stimuli should be nearly complete. After motion adaptation, the perception of global movement direction in partially coherent random dot kinematograms (RDKs) is temporarily impaired if the predominant direction of dots in the test stimulus matches that of the adaptation stimulus. I measured the IOT of this motion incoherence aftereffect in four observers. Post-adaptation motion coherence thresholds were elevated equally for interocular and intraocular adaptation, indicating complete transfer of the aftereffect. Measurement of the classical motion aftereffect using the same stimuli and conditions showed partial or absent transfer. These data support the idea that extrastriate areas play a key role in motion perception and suggest that the motion incoherence aftereffect and the classical motion aftereffect may involve different mechanisms.

Adaptation, Ocular↗
PubMed1993

Organizational factors and the perception of motion in depth.

When two stationary, stereoscopically separated targets are viewed in a completely dark surround, and no cues concerning their egocentric distances from the observer are salient, the farther target tends to be seen at the same distance it would have assumed if it were by itself. The nearer target is seen as being closer than it would have been if seen alone. The present studies extend this previous finding (now termed the far-anchor effect) into the domain of targets that move in stereoscopic space. Observers viewed two small illuminated targets, which began at either the same or different stereoscopic distances. One of the targets was moved in depth and the observers identified the target that appeared to move. Conditions varied according to the initial depth location of the moving target. Significantly more correct responses were reported when the nearer target moved than when the farther one moved, consistent with the hypothesis that the perception of motion in depth is affected by the aforementioned perceptual anchoring effect of the farther target.

Acceleration↗
PubMed1984

Optokinetic and vection responses to apparent motion in man.

Apparent motion was investigated as a stimulus for optokinetic nystagmus (OKN) and self-motion perception (vection). Apparent motion was stimulated by stroboscopically illuminating vertical stripes on the interior of a large drum that rotated about the observer at 20, 40 and 60 deg/sec. We determined threshold stroboscopic frequencies (f) for the appearance of smooth continuous apparent motion and measured responses of pursuit, OKN, optokinetic after nystagmus (OKAN) and vection, to stroboscopic frequencies at, above and below f. Pursuit occurred for all of these stimuli. However OKN, OKAN and vection only occurred for frequencies equal to or greater than the threshold for continuous apparent motion. Our results suggest that pursuit can occur as a response to apparent motion generated by both small and large image displacements, while OKN and vection are responses to apparent motion generated by small image displacements only. These results suggest that different afferent sources are utilized for the control of pursuit and of the slow phase of OKN.

Afterimage↗
PubMed2003

Neuronal mechanisms for detection of motion in the field of view.

The visual system cannot rely only upon information from the retina to perceive object motion because identical retinal stimulations can be evoked by the movement of objects in the field of view as well as by the movements of retinal images self-evoked by eye movements. We clearly distinguish the two situations, perceiving object motion in the first case and stationarity in the second. The present work deals with the neuronal mechanisms that are likely involved in the detection of real motion. In monkeys, cells that are able to distinguish real from self-induced motion (real-motion cells) are distributed in several cortical areas of the dorsal visual stream. We suggest that the activity of these cells is responsible for motion perception, and hypothesize that these cells are the elements of a cortical network representing an internal map of a stable visual world. Supporting this view are the facts that: (i) the same cortical regions in humans are activated in brain imaging studies during perception of object motion; and (ii) lesions of these same regions produce selective impairments in motion detection, so that patients interpret any retinal image motion as object motion, even when they result from her/his eye movements. Among the areas of the dorsal visual stream rich in real-motion cells, V3A and V6, likely involved in the fast form and motion analyses needed for visual guidance of action, could use real-motion signals to orient the animal's attention towards moving objects, and/or to help grasping them. Areas MT/V5, MST and 7a, known to be involved in the control of pursuit eye movements and in the analysis of visual signals evoked by slow ocular movements, could use real-motion signals to give a proper evaluation of motion during pursuits.

Animals↗
PubMed2000

Motion energy versus position tracking: spatial, temporal, and chromatic parameters.

The fundamental question in motion perception is whether motion is an interpretation imposed on an object or feature perceived at separate positions at sequential instants, or whether it is the response of direction-sensitive detectors that can extract the motion-energy in the stimulus, i.e. the orientation of spatio-temporal energy. To answer this question we constructed stimuli whose position changed in one direction while the motion energy contained in the same spatial frequency moved in the same or the opposite direction (by superimposing moving sinusoidal gratings on stationary gratings of the same spatial frequency and orientation). In every case tested (0.25-25 Hz temporal frequency; 0.25-1.0 cyc/deg spatial frequency; achromatic and equiluminant contrast), the perceived direction of motion was in the direction of motion energy, indicating the existence of neurons which compute motion direction without explicitly computing spatial position. The measurements also confirmed that motion-energy computations can be modeled as separable in spatial and temporal frequency.

Adult↗
PubMed1998

Cortical fMRI activation produced by attentive tracking of moving targets.

Attention can be used to keep track of moving items, particularly when there are multiple targets of interest that cannot all be followed with eye movements. Functional magnetic resonance imaging (fMRI) was used to investigate cortical regions involved in attentive tracking. Cortical flattening techniques facilitated within-subject comparisons of activation produced by attentive tracking, visual motion, discrete attention shifts, and eye movements. In the main task, subjects viewed a display of nine green "bouncing balls" and used attention to mentally track a subset of them while fixating. At the start of each attentive-tracking condition, several target balls (e.g., 3/9) turned red for 2 s and then reverted to green. Subjects then used attention to keep track of the previously indicated targets, which were otherwise indistinguishable from the nontargets. Attentive-tracking conditions alternated with passive viewing of the same display when no targets had been indicated. Subjects were pretested with an eye-movement monitor to ensure they could perform the task accurately while fixating. For seven subjects, functional activation was superimposed on each individual's cortically unfolded surface. Comparisons between attentive tracking and passive viewing revealed bilateral activation in parietal cortex (intraparietal sulcus, postcentral sulcus, superior parietal lobule, and precuneus), frontal cortex (frontal eye fields and precentral sulcus), and the MT complex (including motion-selective areas MT and MST). Attentional enhancement was absent in early visual areas and weak in the MT complex. However, in parietal and frontal areas, the signal change produced by the moving stimuli was more than doubled when items were tracked attentively. Comparisons between attentive tracking and attention shifting revealed essentially identical activation patterns that differed only in the magnitude of activation. This suggests that parietal cortex is involved not only in discrete shifts of attention between objects at different spatial locations but also in continuous "attentional pursuit" of moving objects. Attentive-tracking activation patterns were also similar, though not identical, to those produced by eye movements. Taken together, these results suggest that attentive tracking is mediated by a network of areas that includes parietal and frontal regions responsible for attention shifts and eye movements and the MT complex, thought to be responsible for motion perception. These results are consistent with theoretical models of attentive tracking as an attentional process that assigns spatial tags to targets and registers changes in their position, generating a high-level percept of apparent motion.

Adult↗
PubMed1999

Vestibular and vestibulo-proprioceptive perception of motion in the horizontal plane in blindfolded man--II. Estimations of rotations about the earth-vertical axis.

Perception of angular displacement in the horizontal plane was studied in blindfolded human subjects. Subjects sitting on a rotating chair were turned and turned themselves about the earth-vertical axis. Magnitudes of left- and rightward directed rotations were in steps of 30 degrees and overlapped an entire circle. The averaged relative angular error in estimation of passive turns was 0.19 +/- 0.014 (M +/- m), that of active turns 0.16 +/- 0.011. Passively rotated subjects tended to overestimate turns with an increase in the rotation magnitude. Estimations of passive turns were linearly related to the turn magnitude (Y= -0.357+1.065X; R2=0.864). When turning themselves, subjects tended to overestimate rotations of lower magnitudes and underestimate those of higher magnitudes. Linearity was observed between estimations of active turns and their magnitude (Y=26.456+0.862X; R2=0.857). Turn estimation is regarded as a geometrical task, which associates subjectively defined angular and linear parameters of circular motion. It is proposed that during rotation blindfolded subjects perceive the horizontal plane as a heterometric space, the extent of which depends on the estimation of a turn.

Adult↗
PubMed2004

Jitter and size effects on vection are immune to experimental instructions and demands.

Both coherent perspective jitter and explicit changing-size cues have been shown to improve the vection induced by radially expanding optic flow. We examined whether these stimulus-based vection advantages could be modified by altering cognitions and/or expectations about both the likelihood of self-motion perception and the purpose of the experiment. In the main experiment, participants were randomly assigned into two groups-one where the cognitive conditions biased participants towards self-motion perception and another where the cognitive conditions biased them towards object-motion perception. Contrary to earlier findings by Lepecq et al (1995 Perception 24 435-449), we found that identical visual displays were less likely to induce vection in 'object-motion-bias' conditions than in 'self-motion bias' conditions. However, significant jitter and size advantages for vection were still found in both cognitive conditions (cognitive bias effects were greatest for non-jittering same-size control displays). The current results suggest that if a sufficiently large vection advantage can be produced when participants are expecting to experience self-motion, it is likely to persist in object-motion-bias conditions.

Adult↗