Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Motion”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,369 records · Page 76Linked to original sources
PubMed1999

A computational model of selective deficits in first and second-order motion processing.

Recent neurological studies of selective impairments in first and second-order motion processing are of considerable relevance in elucidating the mechanisms of motion perception in normal human observers. We examine the stimuli which have been used to assess first and second-order motion processing capabilities in clinical subjects, and discuss the nature of the computations necessary to extract their motion. We find that a simple computational model of first and second-order motion processing is able to account for the data. The model consists of a first-order channel computing motion at coarse and fine scales, and a coarse scale second-order channel. The second-order channel is sensitive to motion information defined by variations in luminance, contrast, spatial frequency and flicker. When elements of the model are disabled, its performance on either first or second-order motion can be selectively impaired in line with the neurological data.

Brain Diseases↗
PubMed1999

Global motion processing is not tuned for binocular disparity.

An important goal of the visual system is the segmentation of image features into objects and their backgrounds. A primary cue for this is motion: when a region shares the same pattern of motion it is segregated from its surround. Three experiments were carried out to investigate whether the segmentation of image features on the basis of motion information is facilitated by the addition of binocular disparity. Coherence thresholds were measured for the discrimination of the global direction of motion of random dot kinematograms (RDKs) in which the relative disparity of the signal and noise dots was manipulated. When the signal dots were embedded in a three dimensional cloud of noise dots, coherence thresholds were similar to those measured when signal and noise dots were both presented with zero disparity. However, when the signal dots were separated from the noise dots in depth, global motion processing was strongly facilitated. These results were considered in terms of two models, one in which global motion is processed by disparity tuned mechanisms, the other in which the discrimination of the direction of motion is mediated by an attention-based system. It was concluded that global motion processing is not tuned for binocular disparity and that the facilitation of the discrimination of direction provided by binocular disparity in certain circumstances reflects the rôle of an attention-based system.

Depth Perception↗
PubMed1999

Effects of a benzodiazepine, lorazepam, on motion integration and segmentation: an effect on the processing of line-ends?

Previous studies have shown that the perceptual integration of component motions distributed across space is inhibited whenever segmentation cues, such as line-ends, are salient. Herein, we investigate to what extent enhanced inhibition induced by lorazepam, a benzodiazepine facilitating the fixation of GABA on GABAA receptors, modifies the balance between motion integration and motion segmentation at the behavioural level. Motion integration was tested in 16 healthy volunteers taking a single and oral dose of either placebo or lorazepam (0.038 mg kg-1). The stimulus consisted of an outlined diamond presented behind four, otherwise invisible, apertures and translating along a circular trajectory (Lorenceau & Shiffrar (1992). Vision Research, 32, 263-273). Under these conditions, recovering the global diamond direction requires the integration of the component motions available within each aperture. The observers were asked to discriminate the global, clockwise or counter-clockwise, diamond direction under difficult--at high luminance contrasts--or easy--at low luminance contrasts--conditions. Overall, reaction times and error rates increased in the lorazepam group as compared to the placebo group, suggesting strong non-specific effects. However, the changes in performance in the lorazepam group are not homogeneous across conditions, suggesting that lorazepam also induces specific effects that modulate the integration/segmentation balance. Additional experiments performed with visible apertures or visible diamond vertices indicate that the effects of lorazepam are unlikely to reflect a deficit of motion processing or motion integration mechanisms since performance is only slightly impaired in the lorazepam as compared to the placebo group under these conditions. These results suggest that lorazepam might specifically modulate the saliency of line-ends, presumably because processing these features involves inhibitory mechanisms using GABA as a neuromediator, and in turn modify the balance between motion integration and segmentation.

Anti-Anxiety Agents↗
PubMed1999

Does early non-linearity account for second-order motion?

A contrast-modulated (CM) pattern is formed when a modulating or envelope function imposes local contrast variations on a higher-frequency carrier. Motion may be seen when the envelope drifts across a stationary carrier and this has been attributed to a second-order pathway for motion. However, an early compressive response to luminance (e.g. in the photoreceptors) would introduce a distortion product at the modulating frequency. We used a nulling method to measure the distortion product, and then asked whether this early distortion could account for perception of second-order motion. The first stimulus sequence consisted of alternate frames of CM (100% modulation) and luminance-modulated (LM) patterns. Carriers were either 2-D binary noise (4 x 4 min arc dots) or a 4 c/deg grating, both modulated at 0.6 c/deg. The carrier was stationary while the phase of the modulating signal (LM alternating with CM) stepped successively through 90 degrees to the left or right. Motion was seen in a direction opposite to the phase stepping, consistent with early compressive distortion that induces an out-of-phase LM component into the CM stimulus. We measured distortion amplitude by adding LM to the CM frames to null the perceived motion. Distortion increased as the square of carrier contrast, as predicted by the compressive transducer. It also increased with modulation drift rate, implying that the transducer is time-dependent, not static. Thus early compressive non-linearity does induce first-order artefacts into second-order stimuli. Nevertheless this does not account for second-order motion, since perceived motion of second-order sequences (CM in every frame) could in general not be nulled by adding LM components. We conclude that two pathways for motion do exist.

Contrast Sensitivity↗
PubMed1999

Optimal spatial frequencies for discrimination of motion direction in optic flow patterns.

Spatial frequency tuning functions were measured for direction discrimination of optic flow patterns. Three subjects discriminated the direction of a curved motion path using computer generated optic flow patterns composed of randomly positioned dots. Performance was measured with unfiltered patterns and with patterns that were spatially filtered across a range of spatial frequencies (center spatial frequencies of 0.4, 0.8, 1.6, 3.2, 6.4, and 9.6 c/deg). The same subjects discriminated the direction of uniform, translational motion on the fronto-parallel plane. The uniform motion patterns were also composed of randomly positioned dots, that were either unfiltered or filtered with the same spatial filters used for the optic flow patterns. The peak spatial frequency was the same for both the optic flow and uniform motion patterns. For both types of motion, a narrow band (1.5 octaves) of optimal spatial frequencies was sufficient to support the same level of performance as found with unfiltered, broadband patterns. Additional experiments demonstrated that the peak spatial frequency for the optic flow patterns varies with mean image speed in the same manner as has been reported for moving sinusoidal gratings. These findings confirm the hypothesis that the outputs of the local motion mechanisms thought to underlie the perception of uniform motion provide the inputs to, and constrain the operation of, the mechanism that processes self motion from optic flow patterns.

Computer Graphics↗
PubMed2000

Luminance processing in apparent motion, Vernier offset and stereoscopic depth.

We obtained (apparently) linear responses to luminance from three special displays of apparent motion, Vernier offset and stereoscopic depth. In our motion stimulus a dark and a light bar exchanged luminances repetitively on a grey surround. Motion was attributed to the bar that differed more from the surround, that is, on a dark surround the light bar appeared to jump, and on a light surround the dark bar appeared to jump. The apparent motion disappeared when the luminance of the surround lay halfway between that of the bars--on a linear, not a logarithmic scale. Similar results were obtained for special Vernier offset and stereo stimuli. These results cannot be explained if all luminances are processed within the same luminance pathway and that pathway transforms input luminance using non-linear compression. However, the apparent linearity of our results could arise from opposite and equal non-linearities cancelling out within separate ON- and OFF-spatial luminance pathways. A second set of experiments presented one bar separately into each eye on different surrounds (dichoptic presentation of competing apparent motion signals) or manipulated the display spatially so that different surrounds were associated with different bars (binocular presentation of competing Vernier targets). Results showed that apparent motion and Vernier signals of equal Weber contrast (normalisation of linear difference to surround luminance) evoked equal-motion and equal Vernier offset strengths. Given that motion and Vernier strength followed Weber's law, we infer that the ON- and OFF-pathways transform luminance non-linearly. Our third experiment presents an example of a brightness bisection task in which we were able to influence the bisection steps, to follow either a linear or non-linear series. The benefits of parsing the visual scene so that visual information is processed within two opposite luminance pathways is discussed.

Contrast Sensitivity↗
PubMed2004

'Double-blindsight' revealed through the processing of color and luminance contrast defined motion signals.

Background perturbation techniques using both static and dynamic luminance contrast and chromatic contrast noise have been employed to investigate the interaction between luminance and chromatic contrast signals. A number of experiments involving contrast detection thresholds for static stimuli, simple reaction times, and pupil color responses yield evidence for independent processing of luminance and color signals. One exception is the perception of color-defined coherent motion of randomly distributed checks when dynamic, luminance-defined, motion signals can disrupt completely the perception of coherent motion. When the moving stimulus contains color-defined, recognizable features that are spatially distinct from background noise, the perception of coherent motion is restored and becomes completely independent of dynamic luminance contrast noise. Feature-tracking mechanisms must therefore play a major part in the detection of color-defined motion. Other findings reveal the existence of a motion channel that receives exclusively achromatic inputs and a separate channel that extracts and combines luminance contrast and color-defined motion signals. Further studies carried out to investigate the interaction between luminance and chromatic signals show that color-defined, position-change thresholds are mediated by motion detection mechanisms and are, therefore, also disrupted by dynamic luminance contrast noise. In spite of the perceived uncertainty of spatial location, other experiments show that accurate, color-defined position information is preserved and available for use in other tasks. For example, accurate position information can be used to detect the vertical misalignment of color-defined checks, independently of luminance contrast noise, even when position-change thresholds are severely impaired. The analogy with 'blindsight' is obvious and irresistible. 'Blindsight' describes the ability to make accurate use of visual information in the absence of conscious visual perception. The findings that have emerged from this investigation reveal the ability of normal subjects to discard misleading, consciously perceived visual signals. The ability to override perception and to make good use of accurate visual information, in spite of misleading percepts, can best be described as 'Double-blindsight'.

Awareness↗
PubMed2006

Fixational eye movements and motion perception.

Small eye movements are necessary for maintained visibility of the static scene, but at the same time they randomly oscillate the retinal image, so the visual system must compensate for such motions to yield the stable visual world. According to the theory of visual stabilization based on retinal motion signals, objects are perceived to move only if their retinal images make spatially differential motions with respect to some baseline movement probably due to eye movements. Motion illusions favoring this theory are demonstrated, and psychophysical as well as brain-imaging studies on the illusions are reviewed. It is argued that perceptual stability is established through interactions between motion-energy detection at an early stage and spatial differentiation of motion at a later stage. As such, image oscillations originating in fixational eye movements go unnoticed perceptually, and it is also shown that image oscillations are, though unnoticed, working as a limiting factor of motion detection. Finally, the functional importance of non-differential, global motion signals are discussed in relation to visual stability during large-scale eye movements as well as heading estimation.

Afterimage↗
PubMed2002

Apparent motion processing in strabismic observers with varying levels of stereo vision.

Deficits of motion processing have been reported in individuals with infantile strabismus. Here we examined motion perception in early and late onset strabismic individuals with varying levels of stereo acuity using the Fine Grain Motion Illusion (FGMI). The FGMI is an illusion of motion, where under some conditions, observers report exaggerated motion. It has been speculated that this illusion is due to the spatial range of cortical cells stimulated. We used this illusion to compare this motion exaggeration in the central vision of both the deviating and non-deviating eye of strabismic observers with control eyes. While individuals with early onset strabismus showed some mild exaggeration of motion, those with low stereo acuity, regardless of age at onset, showed significantly larger exaggeration of this motion illusion in both the deviating and non-deviating eyes as compared with control observers. These results might indicate that this illusion and stereopsis involve common mechanisms.

Adolescent↗
PubMed2002

Fundamental mechanisms of visual motion detection: models, cells and functions.

Taking a comparative approach, data from a range of visual species are discussed in the context of ideas about mechanisms of motion detection. The cellular basis of motion detection in the vertebrate retina, sub-cortical structures and visual cortex is reviewed alongside that of the insect optic lobes. Special care is taken to relate concepts from theoretical models to the neural circuitry in biological systems. Motion detection involves spatiotemporal pre-filters, temporal delay filters and non-linear interactions. A number of different types of non-linear mechanism such as facilitation, inhibition and division have been proposed to underlie direction selectivity. The resulting direction-selective mechanisms can be combined to produce speed-tuned motion detectors. Motion detection is a dynamic process with adaptation as a fundamental property. The behavior of adaptive mechanisms in motion detection is discussed, focusing on the informational basis of motion adaptation, its phenomenology in human vision, and its cellular basis. The question of whether motion adaptation serves a function or is simply the result of neural fatigue is critically addressed.

Adaptation, Physiological↗
PubMed2003

An event-related potentials study of biological motion perception in humans.

In order to clarify the neural dynamics involved in the perception of biological motion, we recorded event-related potentials from 12 subjects. The subjects were shown biological motion or scrambled motion as a control stimulus. In the scrambled motion, each point had the same velocity vector as in the biological motion, but the initial starting positions were randomized. The perception of both biological and scrambled motion elicited negative peaks at around 200 (N200) and 240 ms (N240). Furthermore, both negative peaks were significantly larger in the biological motion condition than in the scrambled motion condition over the right occipitotemporal region. In light of previous human neuroimaging studies, we speculate that component N200 is generated near the extrastriate cortex area and N240 is generated from the superior temporal sulcus region.

Adult↗
PubMed1998

Evaluating sensory conflict and postural instability. Theories of motion sickness.

Two experiments were carried out to evaluate the sensory conflict and the postural instability theories of motion sickness. The central hypothesis of sensory conflict theory is that motion sickness is caused by conflict between the current pattern of sensory inputs about self-movement and the pattern that is expected on the basis of previous experience. A subsidiary hypothesis is that the degree of motion sickness is proportional to the magnitude of sensory conflict. The central hypothesis of postural instability theory is that motion sickness is caused by loss of postural control. A subsidiary hypothesis is that the degree of motion sickness is proportional to amount of postural instability, which can be manipulated by physical restraint. In both experiments there were two levels of sensory conflict and two levels of postural restraint. Dependent variables were latency of onset and severity of motion sickness. The widespread occurrence of motion sickness in both experiments clearly confirmed the main hypothesis of sensory conflict theory. The results from Experiment 1, that there was significantly more motion sickness in the restrained condition, and from Experiment 2, that there was no significant difference in symptoms between the two restraint conditions, provide no support for the subsidiary hypothesis of postural instability theory. Evidence relating to the subsidiary proposition of sensory conflict theory was inconsistent.

Adolescent↗
PubMed1996

Correlation of measured range of hip motion following total hip arthroplasty and responses to a questionnaire.

Twenty-eight patients (with 30 primary and 8 revision total hip arthroplasties) completed a standardized questionnaire containing the Western Ontario and McMaster Universities (WOMAC) osteoarthritis index and Harris hip score questions prior to an office visit a minimum of 1 year after surgery. The range of hip motion measured by an orthopaedic surgeon was compared with the responses to questions on stiffness and function as well as with global scores in the WOMAC osteoarthritis index. Patient responses to the questions asking if they could cut their toenails on the operated side and the Harris hip score question asking if they could put on socks and tie a shoe correlated significantly with postoperative hip motion (P < .005). The WOMAC global pain and stiffness scores did not correlate with range of motion. The WOMAC physical function score correlated significantly only with hip flexion (P < .05). Of the WOMAC physical function questions, difficulty bending to pick an object off the floor (P < .05) and getting on and off the toilet (P < .05) correlated with the sum of the range of motion in all planes and weighted Harris hip score range of motion calculation. These data suggest that the points allocated in the Harris hip score for range of motion can be estimated reasonably accurately from questionnaire or phone response to a series of questions on a standardized questionnaire. The question on ability to cut toenails or the Harris hip score question regarding ability to put on socks and tie a shoe correlated with the most individual planes of motion, but several WOMAC physical function questions also correlated with total and weighted range of motion calculations.

Activities of Daily Living↗
PubMed2003

A higher order motion region in human inferior parietal lobule: evidence from fMRI.

The proposal that motion is processed by multiple mechanisms in the human brain has received little anatomical support so far. Here, we compared higher- and lower-level motion processing in the human brain using functional magnetic resonance imaging. We observed activation of an inferior parietal lobule (IPL) motion region by isoluminant red-green gratings when saliency of one color was increased and by long-range apparent motion at 7 Hz but not 2 Hz. This higher order motion region represents the entire visual field, while traditional motion regions predominantly process contralateral motion. Our results suggest that there are two motion-processing systems in the human brain: a contralateral lower-level luminance-based system, extending from hMT/V5+ into dorsal IPS and STS, and a bilateral higher-level saliency-based system in IPL.

Adult↗
PubMed2002

Is experimental motion blindness due to sensory suppression? An ERP approach.

Recent psychophysical studies have revealed attentional modulation of visual motion perception and interest now focuses on the locus of this interaction. Using event-related brain potentials (ERPs) we examined whether transient motion blindness evoked in a dual task [Vision Res. 41 (2001) 1613-1617] is related to a selection process occurring at the stage of sensory processing or at a higher level. In our paradigm, a particular change of colour of the fixation point cued the subject to detect a brief episode of coherent random dot motion embedded in a succession of episodes of incoherent motion. Detection of the coherent motion was significantly impaired when it occurred simultaneously with the colour cue, and recovered over the subsequent 300 ms. This functional relationship was reflected in the amplitude of a sensory, motion-evoked component (N200), and in a late positive complex (P300). However, a direct comparison of ERPs produced by stimuli that were detected or missed revealed differences only in the P300 component. These results indicate that attenuation of sensory motion processing does not account for this transient, attention-induced deficit in visual motion perception.

Adult↗
PubMed2001

Asynchronous processing in vision: color leads motion.

It has been demonstrated that subjects do not report changes in color and direction of motion as being co-incidental when they occur synchronously. Instead, for the changes to be reported as being synchronous, changes in direction of motion must precede changes in color. To explain this observation, some researchers have suggested that the neural processing of color and motion is asynchronous. This interpretation has been criticized on the basis that processing time may not correlate directly and invariantly with perceived time of occurrence. Here we examine this possibility by making use of the color-contingent motion aftereffect. By correlating color states disproportionately with two directions of motion, we produced and measured color-contingent motion aftereffects as a function of the range of physical correlations. The aftereffects observed are consistent with the perceptual correlation between color and motion being different from the physical correlation. These findings demonstrate asynchronous processing for different stimulus attributes, with color being processed more quickly than motion. This suggests that the time course of perceptual experience correlates directly with that of neural activity.

Color Perception↗
PubMed1996

A direct demonstration of functional specialization within motion-related visual and auditory cortex of the human brain.

BACKGROUND: Physiological studies of the macaque brain have shown that there is a large expanse of visual cortex, the V5 complex, which is specialized for visual motion, and that several areas within V5 are specialized for different kinds of visual motion. In continuing work on motion-related visual cortex, we wished to chart the specialized visual motion areas in the human brain and to determine their anatomical relationship. Human subjects viewed different motion displays, and the cortical location of the increased activity produced by each stimulus was recorded. The technique of functional magnetic resonance imaging (fMRI) was used, in order to image the same subjects repeatedly. RESULTS: We found that each of the three motion stimuli activated specific parts of the V5 complex. These sites of activation overlap with V5 and, to a smaller extent, with each other. Unexpectedly, the three motion stimuli also activated neighbouring, but nonoverlapping, regions of auditory cortex that are normally activated by the perception of speech. CONCLUSIONS: The three sites of activation produced by the visual motion stimuli occupy adjacent territories within the V5 complex. Components of the V5 complex are specifically connected to regions within auditory cortex.

Auditory Cortex↗
PubMed1998

Close correlation between activity in brain area MT/V5 and the perception of a visual motion aftereffect.

Studies in primate physiology and human functional neuroimaging have convincingly shown that the area of the brain termed MT/V5(+)-which includes the middle temporal visual area MT/V5 along with adjacent motion-sensitive areas such as MST--is involved in the processing of motion information [1,2]. Tootell et al. [3] showed that the blood oxygenation level dependent (BOLD) signal measured by functional magnetic resonance imaging (fMRI) in the human MT/V5+ seemingly correlates with the strength of perceived motion aftereffect (MAE), the illusory motion of a stationary pattern that one sees after adapting to a moving pattern [4]. The signal in MT/V5+ decayed slowly during the period when the MAE was seen. It is possible that this slow decrease in MT/V5+ activity was unrelated to the perceptual experience of motion. After replicating Tootell et al.'s experiment, a modified version of the experiment was conducted in which a blank period was inserted between the adapting motion stimulus and the stationary testing pattern. The results demonstrated that MT/V5+ activity indeed decayed more slowly after an effective unidirectional motion adaptation than after bidirectional adaptation, without corresponding perception of MAE. Nevertheless, in a more conclusive experiment, we adapted observers to a unidirectional motion for a very long period and showed that the activity in MT/V5+ changed in synchrony with the presence and absence of perceived MAE, simply as a result of presenting a stationary visual stimulus in and out of the adapted retinal region.

Adaptation, Physiological↗