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At least 1,387 records · Page 77Linked to original sources
PubMed1998

Orientation of selective effects of body tilt on visually induced perception of self-motion.

We examined the effect of body posture upon visually induced perception of self-motion (vection) with various angles of observer's tilt. The experiment indicated that the tilted body of observer could enhance perceived strength of vertical vection, while there was no effect of body tilt on horizontal vection. This result suggests that there is an interaction between the effects of visual and vestibular information on perception of self-motion.

Humans↗
PubMed2006

Activation of area MT/V5 and the right inferior parietal cortex during the discrimination of transient direction changes in translational motion.

The perception of changes in the direction of objects that translate in space is an important function of our visual system. Here we investigate the brain electrical phenomena underlying such a function by using a combination of magnetoencephalography (MEG) and magnetic resonance imaging. We recorded MEG-evoked responses in 9 healthy human subjects while they discriminated the direction of a transient change in a translationally moving random dot pattern presented either to the right or to the left of a central fixation point. We found that responses reached their maximum in 2 main regions corresponding to motion processing area middle temporal (MT)/V5 contralateral to the stimulated visual field, and to the right inferior parietal lobe (rIPL). The activation latencies were very similar in both regions ( approximately 135 ms) following the direction change onset. Our findings suggest that area MT/V5 provides the strongest sensory signal in response to changes in the direction of translational motion, whereas area rIPL may be involved either in the sensory processing of transient motion signals or in the processing of signals related to orienting of attention.

Adult↗
PubMed2003

Activation of human motion processing areas during event perception.

Observers are able to segment continuous everyday activity into meaningful parts. This ability may be related to processing low-level visual cues, such as changes in motion. To address this issue, the present study combined measurement of evoked responses to event boundaries with functional identification of the extrastriate motion complex (MT+) and the frontal eye field (FEF), two regions related to motion perception and eye movements. The results provided strong evidence that MT+ is activated by event boundaries: Individuals' MT+ regions showed strong responses to event boundaries, and MT+ was collocated with a lateral posterior region that responded at event boundaries. The evidence regarding the FEF was less conclusive: The FEF showed reliable but relatively reduced responses to event boundaries, but the FEF was medial and superior to a frontal area that responded at event boundaries. These results suggest that motion cues, and possibly eye movements, may play key roles in event structure perception.

Adult↗
PubMed2003

Responses of extrastriate cortex to switching perception of ambiguous visual motion stimuli.

We recently found that in bistable apparent motion (AM) both the motion complex (hMT/V5+) and kinetic occipital area (KO) transiently activated whenever perception switched in the spinning wheel illusion. Here, we tested the specificity of this result with another bistable AM stimulus, the dynamic dot quartet, that does not involve kinetic contours. We observed significant activations in hMT/V5+, but not in KO. This indicates that neural activity in functionally specialized extrastriate visual areas during switching perception of ambiguous input depends on stimulus features in a finely tuned way suitable to encode perceptual content in the absence of sensory input changes.

Adult↗
PubMed1997

Spatio-temporal boundary formation: the role of local motion signals in boundary perception.

Spatio-temporal boundary formation (SBF) refers to a perceptual process responsible for perception of moving, bounded surfaces from sequential changes in spatially separated local elements. Previous research has indicated that this process produces perception of global form, continuous boundaries and global motion from spatially and temporally sparse element changes. In the present paper, we sought to distinguish between two classes of models for SBF: form-precedes-motion and motion-precedes-form models. Experiment 1 tested the effects of the addition of spurious motion signals, a manipulation that should affect a motion-precedes-form computation but not a form-precedes-motion computation. Shape identification in a 10-alternative forced-choice procedure was disrupted by this manipulation, supporting the former class of models. A particular computational scheme, edge orientation from motion (EOFM) instantiating a motion-precedes-form model is described and tested in Experiment 2. The EOFM model should be disrupted when initiating element changes occur in a certain type of sequential order, relative to randomly arranged changes. Sequential changes markedly disrupted performance, supporting this EOFM approach. The results favor motion-precedes-form models of SBF and are consistent with the particular computational scheme proposed.

Form Perception↗
PubMed1985

Perception of structure from motion: is projective correspondence of moving elements a necessary condition?

A fundamental assumption of almost all existing computational analyses of the perception of structure from motion is that moving elements on the retina projectively correspond to identifiable moving points in three-dimensional space. The present investigation was designed to determine the psychological validity of this assumption in several different contexts. The results demonstrate that the ability of human observers to perceive structure from motion is much more general than would be reasonable to expect on the basis of existing theory. Observers can experience a compelling kinetic depth effect even when the pattern of optical motion is contaminated by large amounts of visual noise (e.g., where the signal to noise ratio is less than 0.15). Moreover, the optical deformations of shading, texture, or self-occluding contours, which would be treated as noise by existing computational models, are analyzed by human observers as perceptually salient sources of information about an object's three-dimensional form. These results suggest that the modular analyses of visual information that currently dominate the literature will have to be modified if they are to account for the high level of generality exhibited by human observers.

Attention↗
PubMed2006

Perceived self-motion in two visual contexts: dissociable mechanisms underlie perception.

We evaluated the influence of moving visual scenes and knowledge of spatial and physical context on visually induced self-motion perception in an immersive virtual environment. A sinusoidal, vertically oscillating visual stimulus induced perceptions of self-motion that matched changes in visual acceleration. Subjects reported peaks of perceived self-motion in synchrony with peaks of visual acceleration and opposite in direction to visual scene motion. Spatial context was manipulated by testing subjects in the environment that matched the room in the visual scene or by testing them in a separate chamber. Physical context was manipulated by testing the subject while seated in a stable, earth-fixed desk chair or in an apparatus capable of large linear motions, however, in both conditions no actual motion occurred. The compellingness of perceived self-motion was increased significantly when the spatial context matched the visual input and actual body displacement was possible, however, the latency and amplitude of perceived self-motion were unaffected by the spatial or physical context. We propose that two dissociable processes are involved in self-motion perception: one process, primarily driven by visual input, affects vection latency and path integration, the other process, receiving cognitive input, drives the compellingness of perceived self-motion.

Adolescent↗
PubMed1981

Monoptic and dichoptic signals do not cooperate in the perception of a bistable motion display.

Two new conditions of presentation of a bistable motion display are studied, where a competition between monoptic and monoptic plus dichoptic information is supposed to be involved. Data contradict the expectation that a dichoptic motion signal could cooperate with a monocular one. A different interpretation of the combination of monoptic and dichoptic signals is proposed. According to it, the clarity of rotational motions is based upon the evidence, even conflicting, which the two "peripheral" low-level processes separately provide.

Discrimination, Psychological↗
PubMed2000

Movement and mind: a functional imaging study of perception and interpretation of complex intentional movement patterns.

We report a functional neuroimaging study with positron emission tomography (PET) in which six healthy adult volunteers were scanned while watching silent computer-presented animations. The characters in the animations were simple geometrical shapes whose movement patterns selectively evoked mental state attribution or simple action description. Results showed increased activation in association with mental state attribution in four main regions: medial prefrontal cortex, temporoparietal junction (superior temporal sulcus), basal temporal regions (fusiform gyrus and temporal poles adjacent to the amygdala), and extrastriate cortex (occipital gyrus). Previous imaging studies have implicated these regions in self-monitoring, in the perception of biological motion, and in the attribution of mental states using verbal stimuli or visual depictions of the human form. We suggest that these regions form a network for processing information about intentions, and speculate that the ability to make inferences about other people's mental states evolved from the ability to make inferences about other creatures' actions.

Adult↗
PubMed2001

Occipitotemporal activity elicited by viewing eye movements: a magnetoencephalographic study.

The temporal and spatial processing of viewing eye movements was studied by magnetoencephalography (MEG) in six normal subjects. Three visual stimulus types were studied: (1) moving eyes (EYES), (2) moving simulated eyes (SIM), consisting of checks moving in the same spatial location as EYES, and (3) an inwardly moving radial pattern (RADIAL). A large clear MEG component, 1M, with mean peak latency of approximately 170 ms, was seen in the right hemisphere to RADIAL and EYES in all six subjects. The 1M to EYES was significantly longer in latency and smaller in amplitude than that seen to RADIAL. A left hemisphere 1M to EYES and RADIAL was seen in three of six subjects. In all subjects and both hemispheres the equivalent current dipoles (ECD) for EYES and RADIAL were located near the occipitotemporal border, the MT/V5 homologue in humans. The ECD to EYES was significantly more posterior and inferior than that to RADIAL, with a calculated significant separation distance of around 1 cm. No ECD was estimated in the fusiform gyrus, a structure that plays a main role in static face perception. Although the 1M was detected in SIM in all six subjects, our criteria for a reliable ECD could only be satisfied in only one subject. Our results suggest that the cortex of human MT/V5 and its surrounds is active both in the perception of eye motion and motion in general, particularly in the right hemisphere. The areas responsive to eye motion were separable from those responsive to radial motion. These data suggest that there may be specialization within regions of human cortex previously thought to be sensitive to motion in general.

Adult↗
PubMed2000

Phi is not beta, and why Wertheimer's discovery launched the Gestalt revolution.

Max Wertheimer (1880-1943), the founder of the Gestalt School of Psychology, published a monograph on the perception of apparent motion in 1912, which initiated a new direction for a great deal of subsequent perceptual theory and research. Wertheimer's research was inspired by a serendipitous observation of a pure apparent movement, which he called the phi-phenomenon to distinguish it from optimal apparent movement (beta), which resembles real movement. Wertheimer called his novel observation 'pure' because it was perceived in the absence of any object being seen to change its position in space. The phi-phenomenon, as well as the best conditions for seeing it, were not described clearly in this monograph, leading to considerable subsequent confusion about its appearance and occurrence. We review the history leading to the discovery of the phi-phenomenon, and then describe: (i) a likely source for the confusion evident in most contemporary research on the phi-phenomenon; (ii) the best conditions for seeing the phi-phenomenon; (iii) new conditions that provide a particularly vivid phi-phenomenon; and (iv) two lines of thought that may provide explanations of the phi-phenomenon and also distinguish phi from beta.

Gestalt Theory↗
PubMed1984

Upside-down presentation of the Johansson moving light-spot pattern.

In a film produced by Johansson, a group of moving spots, corresponding to lights attached to the main joints of a walker or a runner, gives instantly a vivid impression of a person walking or running. Even when this film was inverted and run backward, some sort of human movement was still perceived. It was perceived more frequently as an upright image of a person moving forward in a very strange manner than as an inverted image of a person moving backward. Such strangeness seemed to arise from the fact that the actor's arms were perceived as legs and vice versa. The phase relations typical of the Johansson pattern are therefore still present when the film is inverted and run backward, leading to the perception of biological motions though these motions are very strange.

Animals↗
PubMed2005

Rapid processing of retinal slip during saccades in macaque area MT.

The primate middle temporal area (MT) is involved in the analysis and perception of visual motion, which is generated actively by eye and body movements and passively when objects move. We studied the responses of single cells in area MT of awake macaques, comparing the direction tuning and latencies of responses evoked by wide-field texture motion during fixation (passive viewing) and during rewarded, target-directed saccades and non-rewarded, spontaneous saccades over the same stationary texture (active viewing). We found that MT neurons have similar motion sensitivity and direction-selectivity for retinal slip associated with active and passive motion. No cells showed reversals in direction tuning between the active and passive viewing conditions. However, mean latencies were significantly different for saccade-evoked responses (30 ms) and stimulus-evoked responses (67 ms). Our results demonstrate that neurons in area MT retain their direction-selectivity and display reduced processing times during saccades. This rapid, accurate processing of peri-saccadic motion may facilitate post-saccadic ocular following reflexes or corrective saccades.

Action Potentials↗
PubMed1995

Thresholds for perception of lateral motion in normal subjects and patients with bilateral loss of vestibular function.

Thresholds for detection of direction of whole-body lateral linear acceleration were determined for normal (N) and labyrinthine defective (LD) subjects. Thresholds for 67% correct detection of direction of acceleration steps for 5 LDs (mean 5.65 cm/s2, peak gradient = 25 cm/s3) were not significantly different from 8 Ns (mean 4.84 cm/s2, peak gradient = 22 cm/s3). High inter-subject variability was found both among the 7 Ns and 3 LDs for detection of parabolic accelerations with some individuals being unable to detect their motion direction. Mean Ns thresholds were 15.2 cm/s2 for a ramp with gradient of acceleration = 2.8 cm/s3, 26.4 cm/s2 for a ramp with gradient = 7.9 cm/s3 and 20.2 cm/s2 for a parabola with second derivative = 1.52 cm/s4. Thresholds for LDs were respectively 19.1 cm/s2, 32 cm/s2 and 26.7 cm/s2. The lower thresholds for acceleration steps demonstrate the important effect of acceleration gradient on motion detection. For all stimuli, thresholds for some LDs could be in the range of Ns showing that somatosensory signals can play a significant role in detecting lateral acceleration.

Acceleration↗
PubMed1991

Calibration of "pokes": psychophysical measurement of computer-generated temporal intervals.

To answer questions raised about the accuracy of temporal intervals used to produce perception of apparent motion, interstimulus intervals generated by a computer were measured using physical and psychophysical procedures. Calibration of such devices was assumed initially to be routine but search of the literature indicated that calibration has been ignored in studies of motion and masking. Direct/physical methods of calibration proved unfeasible for assessing the accuracy of a computer programmed through "poke" procedures because signals for temporal intervals could not be differentiated from the output controlled by the machine's "hardwired" program. The results of psychophysical measurement of temporal intervals indicated that, on the average, differences, "constant errors" between expected/programmed intervals and matches of those intervals generally were less than six milliseconds.

Adolescent↗
PubMed1991

Human perception of structure from motion.

Novel dynamic random-do displays representing a rotating cylinder or a noise-field were used to investigate the perception of structure from motion (SFM) in humans. The finite lifetimes of the points allowed the study of spatiotemporal characteristics with smoothly moving stimuli. In one set of experiments subjects had to detect the change from the unstructured motion to the appearance of the cylinder in a reaction time task. In another set of experiments subjects had to distinguish these two stimuli in a two-alternative forced-choice task. The two major findings were: (1) a relatively constant point lifetime threshold (50-85 msec) for perceiving structure from motion. This threshold is similar to the threshold for estimating velocity and suggests that velocity measurements are used to process SFM; (2) long reaction times for detecting structure (approximately 1 sec). The build-up of performance with time and with increasing numbers of points reflects a process of temporal and spatial integration. We propose that this integration is achieved through the generation of a surface representation of the object. Information from single features on the object appears to be used to interpolate a surface between these local measurements allowing the system to improve perception over extended periods of time even though each feature is present only briefly. Selective masking of the stimulus produced characteristic impairments which suggest that both velocity measurements and surface interpolation are global processes.

Form Perception↗
PubMed1988

Dynamic occlusion and motion parallax in depth perception.

Random-dot techniques were used to examine the interactions between the depth cues of dynamic occlusion and motion parallax in the perception of three-dimensional (3-D) structures, in two different situations: (a) when an observer moved laterally with respect to a rigid 3-D structure, and (b) when surfaces at different distances moved with respect to a stationary observer. In condition (a), the extent of accretion/deletion (dynamic occlusion) and the amount of relative motion (motion parallax) were both linked to the motion of the observer. When the two cues specified opposite, and therefore contradictory, depth orders, the perceived order in depth of the simulated surfaces was dependent on the magnitude of the depth separation. For small depth separations, motion parallax determined the perceived order, whereas for large separations it was determined by dynamic occlusion. In condition (b), where the motion parallax cues for depth order were inherently ambiguous, depth order was determined principally by the unambiguous occlusion information.

Attention↗