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 109 records · Page 6Linked to original sources
PubMed2002

Integration of multiple motion vectors over space: an fMRI study of transparent motion perception.

Visual scenes are frequently composed of objects that move in different directions. To segment such scenes into distinct objects or image planes, local motion cues have to be evaluated and integrated according to criteria of global coherence. When several populations of coherently moving random dots penetrate each other, the visual system tends to assign them to different planes-perceived as transparent motion. This process of integration was studied by changing the angle of motion trajectories with which groups of dots penetrate each other or by varying the spatial constellation of dots moving in opponent directions. Psychophysical testing revealed that stimuli providing almost identical local motion cues could be perceived in three very different ways: (1) as a matrix of stationary flickering dots, (2) as a single surface of coherently moving dots, and (3) as two transparent dot matrices moving in different directions. Behaviorally controlled functional magnetic resonance imaging (fMRI) was used to identify brain regions that contribute to the integration of local motion cues into coherently moving surfaces. Activation of the human motion complex (hMT+/V5) and of areas in the fusiform gyrus (FG) as well as in the intraparietal sulcus (IPS-occ) was correlated with the perception of coherent motion and especially hMT+/V5 took a central role in differentiating transparent motion from single-surface coherent motion.

Adult↗
PubMed2006

Eye movements cannot explain vibration-induced visual motion and motion aftereffect.

Eye movements are thought to account for a number of visual motion illusions involving stationary objects presented against a featureless background or apparent motion of the whole visual field. We tested two different versions of the eye movement account: (a) the retinal slip explanation and (b) the nystagmus-suppression explanation, in particular their ability to account for visual motion experienced during vibration of the neck muscles, and for the visual motion aftereffect following vibration. We vibrated the neck (ventral sternocleidomastoid muscles, bilaterally, or right dorsal muscles) and measured eye movements in conjunction with perceived illusory displacement of an LED presented in complete darkness (N=10). To test the retinal-slip explanation, we compared the direction of slow eye movements to the direction of illusory motion of the visual target. To test the suppression explanation, we estimated the direction of suppressed slow-phase eye movements and compared it to the direction of illusory motion. Two main findings show that neither actual nor suppressed eye movements cause the illusory motion and motion aftereffect. Firstly, eye movements do not reverse direction when the illusory motion reverses after vibration stops. Secondly, there are large individual differences with regards to the direction of eye movements in observers who all experience a similar visual illusion. We conclude that, rather than eye movements, a more global spatial constancy mechanism that takes into account head movement is responsible for the illusion. The results also argue against the notion of a single central signal that determines both perceptual experience and oculomotor behaviour.

Adult↗
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↗
PubMed1996

Undersampling produces non-veridical motion perception, but not necessarily motion reversal, in peripheral vision.

We investigated motion perception in peripheral vision (10-40 deg eccentricity) for drifting gratings above and below the Nyquist limit set by neural sampling of the retinal image. We found that psychometric functions for motion discrimination rarely exhibited worse-than-chance performance indicative of motion reversal. A series of control experiments indicated that failure to demonstrate motion reversal could not be attributed to: (1) failure to detect the contrast of the stimulus; (2) failure to detect the motion of the stimulus; (3) use of an inappropriate range of spatial frequencies. Although consistent motion reversal was not observed, additional experiments demonstrated that motion perception was nevertheless non-veridical for spatial frequencies above the Nyquist limit. These seemingly contradictory results were reconciled by the observation that aliased patterns could appear to move in several different directions, all of which were different from the direction of stimulus, but only of which was opposite to the stimulus direction. Nyquist limits inferred from motion discrimination lie near the predictions for P-ganglion cells in human retina and well above M-cell predictions, which implies the M-cell array is too sparse to account for the limits to verdical motion perception in peripheral vision.

Contrast Sensitivity↗
PubMed1996

Motion integration with dot patterns: effects of motion noise and structural information.

To better understand how local motion detectors merge their responses so as to permit the global determination of objects' movements in the visual field, direction discrimination of performance was measured using a flexible class of moving dots--two sets of dots translating sinusoidally 90 deg out of phase along orthogonal axes. When dots' velocities are combined, a global motion along a circular trajectory emerges, clockwise or counter-clockwise depending on the sign of the phase lag. However, the results of the present experiments indicate that dot patterns are segregated into distinct, but interacting, streams when each dot motion can be accurately determined. In contrast, perceptual coherence of the global motion occurs when each local motion signal is "blurred" by a "motion noise". Direction discrimination performance then increases regularly with both noise amplitude and noise frequency, i.e., noise speed. Performance also increases when relative motion between dots is added. Testing different dot configurations indicates that performance is better for spatial arrangements that display structural properties (a square shape), as compared to overlapping random distributions. Interestingly, when the delay between stimulus onset and motion onset increases up to 300 msec, performance improves when dot patterns convey come form of structural organization but not when the dots are distributed at random. Relations of these results to existing models of motion integration are considered.

Discrimination, Psychological↗
PubMed1996

Motion sensitive cells in the macaque superior temporal polysensory area: response discrimination between self-generated and externally generated pattern motion.

It was previously shown [17] that visual movement sensitive neurons lacking selectivity in the anterior parts of the dorsal superior temporal sulcus (STP) of monkeys exhibited selective responses to externally moved objects and failed to respond to the sight of the animal's own limb movements. This paper describes a series of experiments in which a monkey was trained to operate an apparatus that produced visual motion of a projected two-dimensional patterned stimulus. Single unit responses from STP were recorded and responses to visual motion, produced externally by the experimenter, were compared to the responses to visual motion (of the same pattern) produced by the monkey itself. The majority of the movement sensitive cells giving reliable responses to the pattern motion responded statistically more strongly to the experimenter-induced motion than to the motion induced by the monkey itself. The cell responses were observed not to be affected by the motion velocity and the monkey's motor activity (handle rotation without any visual stimulation) did not affect the cell's spontaneous activity. The results indicate that the response discrimination of STP cells between externally and self-induced stimulus motion is not based on form sensitivity. Moreover, the mechanism which produces the described response selectivity is not only limited to naturally occurring visual consequences of the monkey's own motor activity but is plastic and can extend to arbitrary associations between the monkey's movements and consequent visual motion.

Action Potentials↗
PubMed2004

Preparatory deployment of attention to motion activates higher-order motion-processing brain regions.

We used event-related fMRI to test the hypothesis that preparatory attention modulations occur in higher-order motion-processing regions when subjects deploy attention to internally driven representations in a complex motion-processing task. Using a cued attention-to-motion task, we found preparatory increases in fMRI activity in visual motion regions in the absence of visual motion stimulation. The cue, a brief enlargement of the fixation cross, directed subjects to prepare for a complex motion discrimination task. This preparation activated higher-order and lower-order motion regions. The motion regions activated included temporal regions consistent with V5/MT+, occipital regions consistent with V3+, parietal-occipital junction regions, ventral and dorsal intraparietal sulcus, superior temporal sulcus (STS), posterior insular cortex (PIC), and a region of BA 39/40 superior to V5/MT+ involving the angular gyrus and supramarginal gyrus (A-SM). Consistent with our hypothesis that these motion sensory activations are under top-down control, we also found activation of an extensive frontal network during the cue period, including anterior cingulate and multiple prefrontal regions. These results support the hypothesis that anticipatory deployment of attention to internally driven representations is achieved via top-down modulation of activity in task-relevant processing areas.

Adult↗
PubMed2004

Adaptation to spiral motion: global but not local motion detectors are modulated by attention.

In this study, we investigated the effect of attention on local motion detectors. For this purpose we used logarithmic spirals previously used by Cavanagh and Favreau [Perception, 1980, 9(2), 175-182]. While the adapting stimulus was a rotating logarithmic spiral, the test stimulus was either the same spiral or its mirror image. When superimposed, all contours of the spiral stimulus and its mirror image are 90 degrees apart. Presenting the same spiral during the test period shows adaptation of both local motion detectors and global rotation detectors, whereas showing the mirror-spiral stimulates another set of local motion detectors, and therefore illustrates adaptation at only the global motion level. To manipulate the attentional state of observers, a secondary task was presented during the adaptation phase and observers either performed the task or ignored it. Motion aftereffect (MAE) duration was measured afterwards. While the effects of attention and test stimulus type on MAE duration were both significant, the difference in the MAE strength between the attention-distracted and attention-not-distracted conditions was equal when the test stimulus was the same-spiral or the mirror-spiral, suggesting that attention to spiral motion modulates only global rotation units and does not affect local motion detectors located at V1. Our results are in accord with those reported by Watanabe et al. [Proceedings of the National Academy of Sciences of the USA, 1998, 95(19), 11489-11492] which showed differential modulation of motion processing areas depending on the type of motion being attended. Therefore our data are supportive of the notion that attentional modulation of V1 is highly task-dependent.

Adaptation, Ocular↗
PubMed2005

Detection of motion discontinuities between complex motions.

Three main experiments were performed to evaluate the ability of human observers to detect non-homogeneity in a motion field caused by the presence of two adjacent complex motions, having a common motion component. The detection performance varied significantly depending on the common motion component in the motion field. The highest detection rate was observed when the common motion component was radial or rotational flow. The results imply that the selectivity to the presence of a complex motion in the optic flow depends both on the sensitivity of specialized mechanisms tuned to different complex motions and on inhibition of the units tuned to similar motions.

Adult↗
PubMed2003

Longer VEP latencies and slower reaction times to the onset of second-order motion than to the onset of first-order motion.

We compared visual evoked potentials and psychophysical reaction times to the onset of first- and second-order motion. The stimuli consisted of luminance-modulated (first-order) and contrast-modulated (second-order) 1 cpd vertical sine-wave gratings drifting rightward for 140 ms at a velocity of 6 degrees /s. For each condition, we analysed the latencies and peak-to-baseline amplitudes of the P1 and N2 peaks recorded at Oz. For first-order motion, both P1 and N2 peaks were present at low (3%) contrast (i.e., depth modulations) whereas for second-order motion they appeared only at higher (25%) contrasts. When the two types of motion were equated for visibility, responses were slower for second-order motion than for first-order motion: about 44 ms slower for P1 latencies, 53 ms slower for N2 latencies, and 76 ms slower for reaction times. The longer VEP latencies for second-order motion support models that postulate additional processing steps for the extraction of second-order motion. The slower reaction time to the onset of second-order motion suggests that the longer neurophysiological analysis translates into slower detection.

Adult↗
PubMed2003

Reversed-phi perception with motion-defined motion stimuli.

Perception of reversed-phi with motion-defined motion (MDM) stimuli was examined while varying various parameters including eccentricity. For peripheral viewing, reversed-phi was observed at all displacements between 30 degrees and 135 degrees. The perception most prominent at 90 degrees, but was disrupted by dichoptic presentation. These results suggest operations of an energy-based motion system similar to the first-order motion system for luminance motion, which most likely resides at a relatively early level (cf. [Vision Res. 33 (1993) 533]). For central viewing, reversed motion was observed only for larger displacements. The perceived motion at smaller displacements was predominantly in the forward direction. Transition between the two modes occurred around 90 degrees displacement. In addition, this motion perception was not disrupted by dichoptic presentation. This indicated the operation of a polarity independent matching-based motion system residing at a higher-level. Thus, the results indicate the involvement of at least two separate mechanisms for MDM detection, and that there is a dominance shift between the two systems according to the eccentricity.

Contrast Sensitivity↗
PubMed1999

Computing feature motion without feature detectors: a model for terminator motion without end-stopped cells.

Pointlike object features such as line-endings, have a privileged position in the computation of the veridical direction of object motion. Experiments confirm that the human visual system relies heavily on such features if they are present. It has been proposed that units such as end-stopped cells might be necessary for the computation of feature motion instead of the simple cells used in plaid motion models. Conventional plaid motion models have not been applied to feature motion. We present here a model, based on ordinary simple cells, using two parallel pathways (Fourier and non-Fourier) for the computation of the direction of two dimensional motion. Although similar in structure to popular models of plaid motion, our model includes a novel scheme for contrast normalisation and incorporates spatial pooling at the level of MT cells. The model predictions are consistent with psychophysical results for plaids. Furthermore, it computes directions within 5 degrees of the physical motion of line-endings. It is shown that the non-Fourier signal is necessary for the computation of veridical motion.

Computer Simulation↗
PubMed2003

Human cortical response to incoherent motion on a background of coherent motion.

To investigate whether humans achieve a high sensitivity to coherent motion by excluding the response to incoherent motion, we measured the magnetoencephalographic response to the motion of randomly located dots one half of which moved coherently while the other half moved incoherently. The response was related to the faster motion of either coherent or incoherent motion though the observers saw both. All the estimated response sources were within the extrastriate area. The results indicate that incoherent motion is represented in the neural activity of the human extrastriate area even when the coherent motion is perceived at the same time. The fact that the neural activity for the slower coherent motion is not represented in the magnetic response suggests the existence of interaction between the neural activities for the two motions.

Adult↗
PubMed2000

Reliability of cervical range of motion using the OSI CA 6000 spine motion analyser on asymptomatic and symptomatic subjects.

Cervical range of motion (ROM) is evaluated in both clinical and research settings. This study's purpose was to determine if ROM data obtained with the OSI CA 6000 Spine Motion Analyser (SMA) from asymptomatic and symptomatic cervical subjects were reliable within and between testers. Cervical ROM was measured in all three planes in 30 adult asymptomatic and 20 adult symptomatic subjects. A standardized protocol was used to fit each subject with the OSI SMA cervical hardware. Subjects were tested in a seated position with the trunk stabilized. Subjects performed four trials of each pain-free cervical motion during testing. The hardware was completely removed and replaced by the same tester and ROM trials in all three planes were repeated for intratester asymptomatic and symptomatic reliability. The same procedure was completed by a second tester for asymptomatic intratester and intertester reliability. Repeated measures analysis of variance and intraclass correlation coefficients (ICC [2,1 and 2 k]) were used to analyse intra- and intertester reliability data. Intratester ICCs were 0.85 or higher (except for flexion 0.76) for asymptomatic subjects and 0. 87 or higher (except for flexion 0.68) for symptomatic subjects for all motions. Intertester ICCs were 0.88 or higher for all motions. Standard error of measurements were less than 3.92 degrees for all motions. Measures of cervical spinal ROM obtained with the OSI SMA showed good intertester reliablity for all motions, and good intratester reliability for all motions with the exception of the motion of flexion for one of the examiners, which showed moderate reliability.

Adult↗
PubMed1999

[Noninvasive, accurate and reliable measurement of cervical spine motion with a 3D real-time ultrasound motion analyzer].

AIMS: The kinematic analysis of cervical spine motion is important to assess objectively the effects of therapeutic interventions. In this study, precision and reliability of a 3D ultrasound motion analyser was determined. Using this tool the physiologic range of movement of healthy volunteers was assessed. The aim was to test the clinical practicability of this system. METHODS: The active and passive cervical spine range of motion of 20 healthy volunteers with a mean age of 23 years (range 19-28 years) was determined using a CMS 3D ultrasound realtime motion analyser (Zebris Medizintechnik, Tübingen, Germany). Precision was assessed by comparison with a precision goniometer. Two observers determined the inter-rater and retest reliability and the Pearson correlation coefficients were calculated. RESULTS: The maximum measurement difference between CMS and precision goniometer was 0.6 degree. Inter-rater- and retest reliability correlated significantly (0.84 < r < 0.96, p < 0.001). The range of motion found by the CMS corresponded well with motion values determined using other devices. CONCLUSIONS: The range of motion of the cervical spine can be assessed accurately and reliably using a 3D ultrasound motion analyser. The CMS motion analyser is suitable for clinical practice.

Adult↗
PubMed1989

Motion aftereffects and retinal motion.

Two experiments are described in which it was investigated whether the adaptation on which motion aftereffects (MAEs) are based is a response to retinal image motion alone or to the motion signal derived from the process which combines the image motion signal with information about eye movement (corollary discharge). In both experiments observers either fixated a stationary point or tracked a vertically moving point while a pattern (in experiment 1, a grating; in experiment 2, a random-dot pattern) drifted horizontally across the field. In the tracking condition the adapting retinal motion was oblique. In the fixation condition it was horizontal. In every case in both conditions the MAE was horizontal, in the direction opposite to that of pattern motion. These results are consistent with the hypothesis that the adaptation is a response to the motion signal derived from the comparison of eye and image motion rather than to retinal motion per se. An alternative explanation is discussed.

Adaptation, Ocular↗
PubMed1997

Linear motion aftereffect induced by pure relative motion.

The effect of adaptation to pure relative motion was investigated for the motion aftereffect (MAE) of linear translation motion. In experiment 1, MAE induced by adaptation in the surrounding area was tested. The relative motion signal significantly increased the magnitude of MAE while local MAE in the surrounds was not affected. In experiment 2, MAE observed in the same adapted area was examined while local adaptation was cancelled out. Substantial MAE was found only when the test stimuli included the surroundings, which is considered to be favourable for relative motion mechanisms. These results clearly indicate that MAE is induced by adaptation to pure relative motion as well as by local motion. MAE should be regarded as a composite phenomenon reflecting multiple sites of adaptation including the local and the relative motion levels. The results also provide evidence for the existence of independent detecting mechanisms for relative motion processing.

Adaptation, Physiological↗
PubMed2003

Processing shape, motion and three-dimensional shape-from-motion in the human cortex.

Shape and motion are complementary visual features and each appears to be processed in unique cortical areas. However, object motion is a powerful cue for the perception of three-dimensional (3-D) shape, implying that the two types of information--motion and form--are well integrated. We conducted a series of fMRI experiments aimed at identifying the brain regions involved in inferring 3-D shape from motion cues. For each subject, we identified regions in occipital-temporal cortex that were activated when perceiving: (i) motion in unstructured random-dot patterns, (ii) 2-D and 3-D line drawing shapes, and (iii) 3-D shapes defined by motion cues (shape-from-motion, SFM). We found closely adjacent areas in the lateral occipital region activated by random motion and line-drawing shapes. In addition, we found that the SFM stimuli produced a greater MRI signal in only one of the areas identified with the random motion and line-drawing stimuli: the superior lateral occipital (SLO) region. High-resolution analysis showed that SFM objects and line drawings were processed in separate but adjacent sub-regions in SLO, suggesting that SLO codes object shape but retains topographic segregation based on shape cues. Expanding the analysis to the entire cortex identified a parietal area that had overlapping activation for both SFM and line drawings and increased MRI signal for 3-D versus 2-D shapes, suggesting this area is important for processing shape information.

Brain Mapping↗