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PubMed2002

Are mechanisms for perception of biological motion different from mechanisms for perception of nonbiological motion?

We compared the integration of information over space and time for perceiving different configurations of moving dots: a walking person (biological motion), rigid three-dimensional shapes, and unidirectional coherent motion of all dots (translation). No performance differences in judging walking direction and coherent translation direction were obtained in conditions with constant presentation times and varying number of target dots (integration over space). Depending on the speed of the two-dimensional configurations judgments were either worse or better than the judgments of walking direction. The results for conditions with different presentation times (integration over time) show that information about biological motion is integrated over time that increases with increasing gait period, while two-dimensional unidirectional motion is integrated over constant time independent of speed. The effect is not due to the oscillatory nature of the biological motion since information about a rigid three-dimensional shape is summed over a constant time independent of the period of the motion cycle. This could be interpreted as different neural mechanisms mediating the temporal summation for walking direction compared to detecting the orientation of rigid structure, or the direction of two-dimensional unidirectional motion. Since biological motion is characterized by nonrigidity, it is possible that the form itself is integrated over time and not the motion pattern.

Algorithms↗
PubMed1999

Perceptual organization of apparent motion in the Ternus display.

A typical Ternus display has three sequentially presented frames, in which frame 1 consists of three motion tokens, frame 2 (blank) defines the interstimulus interval, and frame 3 has similar motion tokens with their relative positions shifted to the right. Interestingly, what appears to be a seemingly simple arrangement of stimuli can induce one of two distinct apparent-motion percepts in the observer. The first is an element-motion perception where the left-end token is seen to jump over its two neighboring tokens (inner tokens) to the right end of the display. The second is a group-motion perception where the entire display of the three tokens is seen to move to the right. How does the visual system choose between these two apparent-motion perceptions? It is hypothesized that the choice of motion perception is determined in part by the perceptual organization of the motion tokens. Specifically, a group-motion perception is experienced when a strong grouping tendency exists among the motion tokens belonging to the same frame. Conversely, an element-motion perception is experienced when a strong grouping tendency exists between the inner motion tokens in frames 1 and 3 (i.e. the two tokens that overlap in space between frames). We tested this hypothesis by varying the perceptual organization of the motion tokens. Both spatial (form similarity, 3-D proximity, common surface/common region, and occlusion) and temporal (motion priming) factors of perceptual organization were tested. We found that the apparent-motion perception of the Ternus display can be predictably affected, in a manner consistent with the perceptual organization hypothesis.

Analysis of Variance↗
PubMed2004

A comparison of auditory and visual apparent motion presented individually and with crossmodal moving distractors.

Unimodal auditory and visual apparent motion (AM) and bimodal audiovisual AM were investigated to determine the effects of crossmodal integration on motion perception and direction-of-motion discrimination in each modality. To determine the optimal stimulus onset asynchrony (SOA) ranges for motion perception and direction discrimination, we initially measured unimodal visual and auditory AMs using one of four durations (50, 100, 200, or 400 ms) and ten SOAs (40-450 ms). In the bimodal conditions, auditory and visual AM were measured in the presence of temporally synchronous, spatially displaced distractors that were either congruent (moving in the same direction) or conflicting (moving in the opposite direction) with respect to target motion. Participants reported whether continuous motion was perceived and its direction. With unimodal auditory and visual AM, motion perception was affected differently by stimulus duration and SOA in the two modalities, while the opposite was observed for direction of motion. In the bimodal audiovisual AM condition, discriminating the direction of motion was affected only in the case of an auditory target. The perceived direction of auditory but not visual AM was reduced to chance levels when the crossmodal distractor direction was conflicting. Conversely, motion perception was unaffected by the distractor direction and, in some cases, the mere presence of a distractor facilitated movement perception.

Acoustic Stimulation↗
PubMed1994

Dissociation between the detection and perception of motion in Alzheimer's disease.

To better understand the damage to the motion pathway that occurs in senile dementia of the Alzheimer type (SDAT), we developed a system to assess separately the conscious perception and unconscious detection of motion in patients with SDAT. Motion perception thresholds were significantly elevated in SDAT (n = 9) compared with controls (n = 12), but motion detection thresholds were normal. This dissociation between the perception and detection of motion in early SDAT parallels histologic evidence of a disconnection between primary and association visual cortices. This disconnection may underlie the severe visual perception deficits seen in SDAT.

Alzheimer Disease↗
PubMed2006

Motion standstill leads to activation of inferior parietal lobe.

Previous studies on motion perception revealed motion-processing brain areas sensitive to changes in luminance and texture (low-level) and changes in salience (high-level). The present functional magnetic resonance imaging (fMRI) study focused on motion standstill. This phenomenon, occurring at fast presentation frequencies of visual moving objects that are perceived as static, has not been previously explored by neuroimaging techniques. Thirteen subjects were investigated while perceiving apparent motion at 4 Hz, at 30 Hz (motion standstill), isoluminant static and flickering stimuli, fixation cross, and blank screen, presented randomly and balanced for rapid event-related fMRI design. Blood oxygenation level-dependent (BOLD) signal in the occipito-temporal brain region MT/V5 increased during apparent motion perception. Here we could demonstrate that brain areas like the posterior part of the right inferior parietal lobule (IPL) demonstrated higher BOLD-signal during motion standstill. These findings suggest that the activation of higher-order motion areas is elicited by apparent motion at high presentation rates (motion standstill). We interpret this observation as a manifestation of an orienting reaction in IPL towards stimulus motion that might be detected but not resolved by other motion-processing areas (i.e., MT/V5).

Adult↗
PubMed1998

Effect of contrast on the perception of moving multiple Gabor patterns.

The present study examined the way in which the perception of motion coherency depends on luminance contrast. Pseudo-plaid patterns were presented to subjects who judged whether coherent motion or component motion of the Gabor patterns was perceived. Michelson contrast, eccentricity, spatial separation, and angular separation between two groups of Gabor patches were varied systematically. When the contrast was high, coherent motion perception was dominant in peripheral viewing but not in foveal viewing. When the contrast was low, coherent motion was perceived at all eccentricities. Under low-contrast conditions and with peripheral viewing, coherent motion was perceived over broader spatial areas and at wider angular separations. The contrast dependency of motion coherency can be qualitatively explained in terms of the relative activity of hypothetical local-motion units in area V1 and global-motion units in area MT of the visual cortex.

Contrast Sensitivity↗
PubMed2004

Cross-modal dynamic capture: congruency effects in the perception of motion across sensory modalities.

This study investigated multisensory interactions in the perception of auditory and visual motion. When auditory and visual apparent motion streams are presented concurrently in opposite directions, participants often fail to discriminate the direction of motion of the auditory stream, whereas perception of the visual stream is unaffected by the direction of auditory motion (Experiment 1). This asymmetry persists even when the perceived quality of apparent motion is equated for the 2 modalities (Experiment 2). Subsequently, it was found that this visual modulation of auditory motion is caused by an illusory reversal in the perceived direction of sounds (Experiment 3). This "dynamic capture" effect occurs over and above ventriloquism among static events (Experiments 4 and 5), and it generalizes to continuous motion displays (Experiment 6). These data are discussed in light of related multisensory phenomena and their support for a "modality appropriateness" interpretation of multisensory integration in motion perception.

Auditory Perception↗
PubMed1985

Differential effects of ambivalent visual-vestibular-somatosensory stimulation on the perception of self-motion.

The direction of perceived self-motion was determined as a function of combined visual-vestibular and vestibulo-somatosensory stimulations about the earth's vertical z-axis by means of a rotary chair and drum system. The predominant influence of concurrent antagonistic vestibular stimulation on circular vection (CV) even at small accelerations has been demonstrated by several studies in the past. The results of the present paper do not confirm the generally assumed influence of the vestibular system on exocentric motion perception, but instead produce evidence of the dominance of the visual channel even at high acceleration levels. Using a joystick to indicate perceived self-motion, we found the following: Constant CV (visual stimulus velocity: 40 degrees/s) could only be cancelled by vestibular stimulations at oppositely directed mean angular accelerations of 26.9 +/- 9.1 degrees/s2. Smaller accelerations led merely to an acceleration level-related decrease in the perceived velocity of CV. Despite a clear decision with respect to the direction of the perceived motion, subjects (Ss) reported dizziness or even strong motion sickness symptoms. Similar results were obtained with vestibulo-somatosensory interactions. The results are interpreted in terms of an intensive visual support in the processing of visual-vestibular signals, particularly at cortical level, assuming a cortical velocity generator (CVG).

Adolescent↗
PubMed2000

A lesion of cortical area V2 selectively impairs the perception of the direction of first-order visual motion.

Lesions of area MT/V5 in monkeys and its presumed homologue, the motion area, in humans impair motion perception, including the discrimination of the direction of global motion in random dot kinematograms. Here we report the results of similar tests on patient TF, who has a discrete and very small, unilateral infarct in the medial superior part of the right occipital cortex. Structural MRI, co-registered in software with a standardized human brain atlas, reveals that the lesion involves area V2. The patient was impaired in his retinotopically corresponding left lower quadrant on several motion tasks including discrimination in random dot kinematograms of direction, speed and motion-defined discontinuity. He was also impaired on tasks selectively involving first-order motion based on luminance contrast but not on second-order motion based on texture contrast. The results show that even though area MT/V5 is intact, motion perception is abnormal and, in particular, his perception of first-order motion is impaired.

Cerebral Infarction↗
PubMed2007

Imaging brain activity during natural vision using CASL perfusion fMRI.

Functional MRI (fMRI) has begun to be used to explore human brain activity during ecological and natural conditions. Arterial spin labeling (ASL) perfusion fMRI provides an appealing approach for imaging sustained brain activity during natural conditions because of its long-term temporal stability and ability to noninvasively quantify absolute cerebral blood flow (CBF). The present study used ASL perfusion fMRI to measure brain activation patterns associated with natural vision by concurrently recording CBF and blood oxygen level-dependent (BOLD) contrasts while subjects were freely viewing a cartoon movie. Reliable quantitative whole-brain CBF values ( approximately 60 mL/100g/min) as well as regional CBF values (45 approximately 80 mL/100g/min) were measured during movie viewing and resting states. The perfusion contrast revealed CBF increases in multiple visual pathway areas and frontal areas, and CBF decreases in ventromedial frontal cortex and superior temporal cortex during movie viewing compared to resting states. Concurrent BOLD contrast revealed similar but weaker activation and deactivation patterns. Regression analyses of both CBF data and BOLD data showed significant associations between activation in the middle temporal (MT) region and subjects' perception of motion. Region of interest analysis based on a priori literature-defined MT demonstrated significant monotonic stepwise associations between the intensity of motion perception and the CBF and BOLD signal changes. These results demonstrate the feasibility of using ASL perfusion fMRI for imaging both sustained and dynamic effects in neural activation during natural and ecologically valid situations, and support the notion of maintained functional segregation and specialization during natural vision.

Adult↗
PubMed1991

On the half-cycle displacement limit of sampled directional motion.

We employed filtered random-dot kinematograms to determine the maximum displacement (dmax) at which sampled directional motion was reliably detected. The images were produced using ideal band-pass filters that varied in lower cut-off frequency (f1), in bandwidth, and in range (alpha) of component orientations that were passed. Results showed that dmax, expressed in cycles of f1, increased with f1 and alpha, and decreased with bandwidth. In many conditions, dmax exceeded half a cycle of f1, a result that appears to contradict predictions from quadrature models of motion detection. However, an account that does not violate the half-cycle limit can be given on two assumptions. First, motion perception is mediated by a population of orientation and frequency-selective sensors that respond correctly to displacements up to half a cycle in the preferred direction. Second, the outputs from all sensors (notably including off-axis sensors) are linearly summated to yield perception of motion. A computer simulation based on these assumptions provided a remarkably close fit to the psychophysical data.

Computer Simulation↗
PubMed2004

Blindness to inconsistent local signals in motion transparency from oscillating dots.

Visual processing involves hierarchical stages in which local features are initially analyzed and subsequently grouped into objects and surfaces. In the domain of motion perception, transparent motion has been used as a powerful tool to investigate the mechanisms underlying the grouping of local features. Here, we report a novel way of creating motion transparency from oscillating dots (MTOD). In this stimulus, individual dots move back and forth over a small distance. When the dots are oscillating in synchrony, global surfaces are also perceived as moving back and forth. However, when the oscillation desynchronizes, the percept turns into two moving surfaces that are sliding over each other continuously (streaming motion). The percept of MTOD is similar to conventional transparent motion, where individual dots move only in one direction. Also, when streaming motion is perceived, the detection of oscillation is impaired. This blindness to the oscillation becomes stronger, as the signal strength for the streaming motion is increased. These findings suggest that when global visual representations are constructed, weak and inconsistent local signals are discarded.

Humans↗
PubMed2002

Visual processing and neuropsychological function in schizophrenia and schizoaffective disorder.

Persons with schizophrenia and schizoaffective disorder exhibit deficits in both visual processing and neuropsychological tasks. Little is known, however, about whether these deficits are related to one another. We administered psychophysical tests of visual discrimination and recognition, and neuropsychological tests of abstract flexibility, verbal learning, visual memory, working memory and attention to 42 outpatients with stable but chronic schizophrenia or schizoaffective disorder. Multiple regression analyses were performed to determine the relationship between these measures of neuropsychological function and visual psychophysical performance. Results indicated that motion perception was associated with working memory, and that the addition of a memory component to motion perception (motion recognition) was associated with both working memory and visual memory. Visual performance was not associated with symptom severity as measured by the PANSS. These results suggest that psychophysical tests of visual processing may contribute to deficits on neuropsychological tests of visual cognition, and may also reflect cross-modal disturbances of working memory function.

Adult↗
PubMed1997

Perception of motion direction in luminance- and contrast-defined reversed-phi motion sequences.

Nonlinear processing can be used to recover the motion of contrast modulations of binary noise patterns. A nonlinear stage has also been proposed to explain the perception of forward motion in motion sequences which typically elicit reversed-phi. We examined perceived direction of motion for stimuli in which these reversed motion sequences were used to modulate the contrast of binary noise patterns. A percept of forward motion could be elicted by both luminance-defined and contrast-defined stimuli. The perceived direction of motion seen in the contrast-defined stimuli showed a profound carrier dependency. The replacement of a static carrier by a dynamic carrier can reverse the perceived direction of motion. Forward motion was never seen with dynamic carriers. For luminance- and contrast-defined patterns the reversed motion percept increasingly dominated, with increases in the spatial frequency and temporal frequency of the modulation. Differences in the patterns of responses to the two stimuli over spatial and temporal frequency were abolished by the addition of noise to the luminance-defined stimulus. These data suggest the possibility that a single mechanism may mediate the perception of luminance- and contrast-defined motion.

Contrast Sensitivity↗
PubMed1986

Necessary conditions for the perception of motion in depth.

This study investigated the relation between the perception of motion in depth and ocular vergence movements for a single foveally viewed dot, and for a 30 deg X 30 deg pattern of many dots. When the target's disparity was changed, it appeared to move in depth relative to stationary reference marks, but removing the reference marks completely abolished the sensation of motion in depth for the multi-dot target and left only a weak sensation of motion in depth for the single dot target. However, it is not the case that motion-in-depth sensation per se depends on the presence of reference marks; motion in depth generated by changing-size stimulation was unaffected by removing reference marks. Possible explanations for the loss of motion-in-depth sensation include ocular vergence exactly tracked stimulus motion; vergence changes and disparity changes, though unequal, produced equal and opposite motion-in-depth signals; vergence changes, though producing no motion-in-depth signals, suppressed the signals produced by disparity changes; motion-in-depth sensation requires relative motion. Explanation is rejected because vergence tracking errors were large. Explanation is rejected because vergence changes do not in themselves induce a sensation of motion in depth. Explanation is rejected because motion-in-depth threshold is not affected by vergence changes. Conclusions are as follows. For a single-dot target, visual sensitivity to motion in depth is much higher for changes in relative retinal disparity than for changes in absolute retinal disparity, while for a multi-dot target any residual sensitivity is abolished by an interaction between neighboring coherently moving dots. The authors suggest that the relative velocity elements proposed to explain sensitivity to changing size feed the stereomotion mechanism also.

Depth Perception↗
PubMed2003

Can spatial and temporal motion integration compensate for deficits in local motion mechanisms?

We studied the motion perception of a patient, AMG, who had a lesion in the left occipital lobe centered on visual areas V3 and V3A, with involvement of underlying white matter. As shown by a variety of psychophysical tests involving her perception of motion, the patient was impaired at motion discriminations that involved the detection of small displacements of random-dot displays, including local speed discrimination. However, she was unimpaired on tests that required spatial and temporal integration of moving displays, such as motion coherence. The results indicate that she had a specific impairment of the computation of local but not global motion and that she could not integrate motion information across different spatial scales. Such a specific impairment has not been reported before.

Brain Mapping↗