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At least 451 records · Page 25Linked to original sources
PubMed2005

Repetitive TMS over posterior STS disrupts perception of biological motion.

Biological motion perception, the recognition of human action depicted in sparse dot displays, is supported by a network of brain areas including the human posterior superior temporal sulcus (pSTS). We have used repetitive transcranial magnetic stimulation (rTMS) to temporarily disrupt cortical activity within the pSTS and subsequently measured sensitivity to biological motion. Sensitivity was measured for canonical (upright) point-light animations and for animations inverted 180 deg, a manipulation that renders biological motion more difficult to recognize. Observers were markedly less sensitive to upright biological motion following pSTS stimulation. In contrast, performance remained normal for inverted biological motion following pSTS stimulation, and normal for upright and inverted biological motion following stimulation over visual motion sensitive area MT+/V5. In connection with previous brain imaging results, our findings demonstrate that normal functioning of the posterior STS is required for intact perception of biological motion.

Adult↗
PubMed1999

Perception of coherent motion, biological motion and form-from-motion under dim-light conditions.

Three experiments investigated several aspects of motion perception at high and low luminance levels. Detection of weak coherent motion in random dot cinematograms was unaffected by light level over a range of dot speeds. The ability to judge form from motion was, however, impaired at low light levels, as was the ability to discriminate normal from phase-scrambled biological motion sequences. The difficulty distinguishing differential motions may be explained by increased spatial pooling at low light levels.

Form Perception↗
PubMed1990

Effects of adapting luminance and stimulus contrast on the temporal and spatial limits of short-range motion.

Perception of short-range motion was studied as a function of adapting luminance and of stimulus contrast in computer simulations and in psychophysical experiments. The stimuli were random dots plotted on an oscilloscope in two sequential frames, separated by an inter-stimulus interval (ISI). Both in the simulations and in the empirical studies, we estimated the maximum spatial displacement (dmax) between corresponding dots in the successive frames, and the maximum ISI (tmax) at which coherent motion was perceived 80% of the time. Conceptually, the research was based on a rectified elaborated Reichardt detector with spatial and temporal filters at its inputs. Extant psychophysical and neurophysiological data were employed to provide estimates of the effects of luminance and contrast on the spatial and temporal characteristics of the input filters. Results showed a strong effect of adapting luminance on both the spatial and temporal limits of motion perception: decrements in luminance produced marked increments in both dmax and tmax. However, neither dmax nor tmax was affected by changes in stimulus contrast. These outcomes are entirely consonant with expectations based on the rectified elaborated Reichardt detector. Alternative explanations of the psychophysical results are discussed.

Adaptation, Ocular↗
PubMedDate not supplied

Lesions in cat lateral suprasylvian cortex affect the perception of complex motion.

We examined the effects of bilateral ibotenic acid lesions of cat lateral suprasylvian (LS) cortex on motion perception. Cats were tested on tasks requiring integration of local directional signals, precise judgements of direction and extraction of structure-from-motion. All animals showed permanent deficits in integrating local motion signals. These deficits were most pronounced in the presence of directional noise and at larger spatial displacements. In addition, LS lesions produced a 2-fold loss in the accuracy of direction discrimination and large deficits in the perception of structure-from-motion. All of these losses were most severe during the first few weeks of testing following the lesion. These findings demonstrate that LS cortex plays an important role in the processing of stimuli requiring integration of motion information and limits the spatial scale over which such integration can proceed. Partial improvements in performance with time and/or training may be indicative of post-operative plastic changes in neurons outside of LS cortex.

Animals↗
PubMed2003

Multisensory contributions to the perception of motion.

The ability to process motion is crucial for coherent perception and action. While the majority of studies have focused on the unimodal factors that influence motion perception (see, for example, the other chapters in this Special Issue), some researchers have also investigated the extent to which information presented in one sensory modality can affect the perception of motion for stimuli presented in another modality. Although early studies often gave rise to mixed results, the development of increasingly sophisticated psychophysical paradigms are now enabling researchers to determine the spatiotemporal constraints on multisensory interactions in the perception of motion. Recent findings indicate that these interactions stand over-and-above the multisensory interactions documented previously for static stimuli, such as the oft-cited 'ventriloquism' effect. Neuroimaging and neuropsychological studies are also beginning to elucidate the network of neural structures responsible for the processing of motion information in the different sensory modalities, an important first step that will ultimately lead to the determination of the neural substrates underlying these multisensory contributions to motion perception.

Animals↗
PubMed1997

Movement, activity and action: the role of knowledge in the perception of motion.

This paper presents several approaches to the machine perception of motion and discusses the role and levels of knowledge in each. In particular, different techniques of motion understanding as focusing on one of movement, activity or action are described. Movements are the most atomic primitives, requiring no contextual or sequence knowledge to be recognized; movement is often addressed using either view-invariant or view-specific geometric techniques. Activity refers to sequences of movements or states, where the only real knowledge required is the statistics of the sequence; much of the recent work in gesture understanding falls within this category of motion perception. Finally, actions are larger-scale events, which typically include interaction with the environment and causal relationships; action understanding straddles the grey division between perception and cognition, computer vision and artificial intelligence. These levels are illustrated with examples drawn mostly from the group's work in understanding motion in video imagery. It is argued that the utility of such a division is that it makes explicit the representational competencies and manipulations necessary for perception.

Motion Perception↗
PubMed1989

Acuity for fine-grain motion and for two-dot spacing as a function of retinal eccentricity: differences in specialization of the central and peripheral retina.

The brief presentation in the peripheral field of two closely spaced luminous point stimuli, in rapid sequence, induces the illusion of a single dot moving over an extended path. This fine-grain movement illusion (FGMI) is particularly compelling under conditions of dark adaptation. The strength of the motion percept, assessed by a rating-scale procedure, was found to correlate well, over different flash-flash onset delays, with an objective measure of the illusion requiring discrimination of the direction of the flash-flash sequence. A direction-discrimination measure was used to determine the minimum dot separation that would reliably elicit an FGMI at retinal eccentricities of 5-25 deg. For comparison, measures of static spatial acuity was made based on the minimum angle of resolution of two simultaneous dot flashes, and on the threshold for discriminating the separation of two simultaneous dot flashes with variable initial spacing. The spatial threshold for FGMI was lower than that for each of the static measures at all peripheral eccentricities, and it increased more slowly with eccentricity than the other spatial thresholds, suggesting the involvement of separate visual pathways for generating percepts of motion and percepts of shape or location. The finding that in the periphery the grain for motion detection was finer than that for spatial discrimination constrains a class of motion-perception models that form an initial spatial description of the stimulus and then compute a temporal derivative.

Accommodation, Ocular↗
PubMed2005

Perception of depth and motion from ambiguous binocular information.

The visual system can determine motion and depth from ambiguous information contained in images projected onto both retinas over space and time. The key to the way the system overcomes such ambiguity lies in dependency among multiple cues--such as spatial displacement over time, binocular disparity, and interocular time delay--which might be established based on prior knowledge or experience, and stored in spatiotemporal response characteristics of neurons at an early cortical stage. We conducted a psychophysical investigation of whether a single ambiguous cue (specifically, interocular time delay) permits depth discrimination and motion perception. Data from this investigation are consistent with the predictions derived from the response profiles of V1 neurons, which show interdependency in their responses to each cue, indicating that spatial and temporal information is jointly encoded in early vision.

Cues↗
PubMed1988

The aperture problem--I. Perception of nonrigidity and motion direction in translating sinusoidal lines.

To examine how local velocities from different regions of the visual field combine to form a coherent motion percept, we subjected a sinusoidal line stimulus to translational motion. Horizontal movement of a sinewave line along its axial direction is perceived as nonrigid if the angle at the zero crossing is smaller than a critical angle of about 15 deg. This angle is independent of spatial scale and the number of sinusoidal cycles. To extend the applicability of this concept of angle, we developed a mathematical model to predict an observer's sensitivity to small changes in motion direction based on two assumptions: (1) the computed velocity signal is obtained from the intersection of constraint lines defined by local velocity components, (2) local velocity components are contaminated by noise. Measurement of directional discrimination thresholds of moving targets confirmed our expectations. Thresholds varied as a function of the angle of the local contour independent of spatial scale and in quantitative accord with our assumptions.

Discrimination, Psychological↗
PubMed1995

Activation of area V5 by visual perception of motion demonstrated with echoplanar MR imaging.

Cortical activation in visual association areas known to be responsible for the perception of motion was investigated in two volunteers who viewed a projected animated cartoon periodically "run" and "frozen" during collection of echoplanar MR images. Ten axial, contiguous, 5 mm thick, T2-weighted, gradient-echo images (TE 40 ms, TR 3000 ms) depicting BOLD contrast were acquired through the occipital lobe using a GE Signa 1.5 T system with an advanced NMR operating console. Images were analysed by time series regression modelling estimating power in the MR signal at the ON-OFF frequency of motion. Highly significant activation in response to motion perception was identified in both subjects bilaterally in area V5.

Echo-Planar Imaging↗
PubMed2002

Perception of biological motion without local image motion.

A vivid perception of the moving form of a human figure can be obtained from a few moving light points on the joints of the body. This is known as biological motion perception. It is commonly believed that the perception of biological motion rests on image motion signals. Curiously, however, some patients with lesions to motion processing areas of the dorsal stream are severely impaired in image motion perception but can easily perceive biological motion. Here we describe a biological motion stimulus based on a limited lifetime technique that tests the perception of a moving human figure in the absence of local image motion. We find that subjects can spontaneously recognize a moving human figure in displays without local image motion. Their performance is very similar to that for classic point-light displays. We also find that tasks involving the discrimination of walking direction or the coherence of a walking figure can be performed in the absence of image motion. Thus, although image motion may generally aid processes such as segmenting figure from background, we propose that it is not the basis for the precept of biological motion. Rather, we suggest biological motion is derived from dynamic form information on body posture evolving over time.

Humans↗
PubMed1996

Impairment of the perception of second order motion but not first order motion in a patient with unilateral focal brain damage.

Unlike first order motion, which is based on spatiotemporal variations in luminance, second-order motion relies on spatiotemporal variation of attributes derived from luminance, such as contrast. Here we show that a patient with a small unilateral cortical lesion adjacent to human cortical area MT (V5) has an apparently permanent disorder in perceiving several forms of second-order but not first-order motion in his contralateral visual field. This result indicates that separate pathways for motion perception exist, either as divergent pathways from area MT or even from primary visual cortex, or as separate pathways from subcortical areas to extrastriate visual areas.

Adult↗
PubMed2003

Asynchronous perception of motion and luminance change.

Observers were asked to indicate when a target moving on a circular trajectory changed its luminance. The judged position of the luminance change was displaced from the true position in the direction of motion, indicating differences between the times-to-consciousness of motion and luminance change. Motion was processed faster than luminance change. The latency difference was more pronounced for a small (116-134 ms) than for a large luminance decrement (37 ms). The results show that first-order motion is perceived before an accurate representation of luminance is available. These findings are consistent with current accounts of the flash-lag effect. Two control experiments ruled out that the results were due to a general forward tendency. Localization of the target when an auditory signal was presented did not produce forward displacement, and the judged onset of motion was not shifted in the direction of motion.

Acoustic Stimulation↗