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 91 records · Page 5Linked to original sources
PubMed1994

Motion adaptation governs the shape of motion-evoked cortical potentials.

We recorded visually evoked potentials (VEPs) to motion onset/offset of square-wave gratings (dominant spatial frequency 0.69 c/deg, velocity 4.9 deg/sec, contrast 10%, luminance 15 cd/m2) with three electrode combinations (Oz vs Fz, Oz vs linked ears and parietal vs linked ears). In one experiment (seven subjects), we examined the effect of the duty-cycle of motion vs non-motion (5-80%) on the size of the various motion-evoked components. In another experiment (six subjects, duty-cycle 10%), we examined the effect of motion adaptation on the motion VEP. We observed both a positive VEP component around 110 msec (P1) and a negative component around 180 msec (N200). The amplitude of these components depended on duty-cycle and electrode position: N200 dominated at < or = 20% motion duty-cycle, P1 at > or = 50%; P1 dominated medially, N200 laterally. Motion adaptation enhanced the P1 and reduced the N200 by a factor of 3. Previous controversies regarding the major components of motion-evoked potential may be due to different duty-cycles. The effect of duty-cycle is probably caused by adaptation to the test stimulus; it can be predicted quantitatively by a simple one-parameter model based on the assumption that the VEP amplitude is proportional to the non-adapted proportion of motion-response generators.

Adaptation, Physiological↗
PubMed1996

Cortical dynamics of form and motion integration: persistence, apparent motion, and illusory contours.

How does the visual system generate percepts of moving forms? How does this happen when the forms are emergent percepts, such as illusory contours or segregated textures, and the motion percept is apparent motion between the emergent forms? We develop a neural model of form-motion interactions to explain and simulate parametric properties of psychophysical motion data and to make predictions about how the parallel cortical processing streams V1-->MT and V1-->V2-->MT control form-motion interactions. The model explains how an illusory contour can move in apparent motion to another illusory contour or to a luminance-derived contour; how illusory contour persistence relates to the upper interstimulus interval (ISI) threshold for apparent motion; and how upper and lower ISI thresholds for seeing apparent motion between two flashes decrease with stimulus duration and narrow with spatial separation (Korte's laws). The model accounts for these data by suggesting how the persistence of a boundary segmentation in the V1-->V2 processing stream influences the quality of apparent motion in the V1-->MT stream through V2-->MT interactions. These data may all be explained by an analysis of how orientationally tuned form perception mechanisms and directionally tuned motion perception mechanisms interact.

Contrast Sensitivity↗
PubMed1993

Examining motion in the cervical spine. II: Characterization of coupled joint motion using an opto-electronic device to track skin markers.

Analysis of coupled motion in the cervical spine may be useful in helping to identify injuries. In order to investigate this possibility, the nature of coupled motion in the spine and previous investigations on this subject are reviewed here. An enhanced set of displays are developed for an existing opto-electronic device employed for the non-invasive measurement of movement in the upper spine. This instrument consists of a high resolution motion analysis system which tracks small infrared emitting diodes (IREDs). Kinematic data for the motion of the markers is processed and absolute coordinates for the location of each IRED at any time are tabulated; coupled motion with respect to a fixed calibration frame, as well as for vertebrae relative to each other, is deduced from these. Overall analysis provided by the original device includes assessment of cervical lordosis, thoracic kyphosis, and inter-segmental mobility. Characterization of coupled motion, in particular, involves a series of plots showing principal versus secondary motion. Principal movements include flexion-extension, lateral bending, and axial rotation, corresponding to motion in the sagittal, transverse, and horizontal planes, respectively. Mobility is represented in terms of the direction angles made by virtual vectors orthogonal to the planes made by markers on the head, neck, and shoulders. Development of the enhanced displays and the required refinements are described. Precision of the deduced angles is found to be approximately 1 degree. This representation of coupled motion is expected to be valuable in improving the accuracy of attempts to identify normal versus pathological motion in the cervical spine.

Algorithms↗
PubMed2004

Contrast-reversing global-motion stimuli reveal local interactions between first- and second-order motion signals.

Motion perception appears to be mediated by, at least, two systems: a first-order and a second-order system. To investigate the degree of interaction between these systems, we used a contrast-reversing global-motion stimulus in which the signal dots reverse their contrast polarity as they move. In response to such a stimulus, fullwave-rectifying second-order units would signal motion in the displacement direction and first-order units would signal motion in the opposite direction (reverse-phi motion). If these signals were of equal strength, then any inhibitory interaction between them would lead to motion nulling. Such a situation would account for the failure to perceive coherent motion with such a stimulus in a previous study [Vis. Res. 34 (1994) 2849]. In order to test for this possibility we manipulated the stimulus in order to reduce the strength of the second-order response relative to the first-order response. This was achieved by: decreasing dot contrast; increasing stimulus eccentricity; and increasing dot speed. These manipulations resulted in an increase in the perception of (first-order mediated) reverse-phi motion. We conclude that interaction between first- and second-order motion signals occur at the local-motion-pooling level.

Adaptation, Ocular↗
PubMed1997

Motion integration over space: interaction of the center and surround motion.

Motion integration occurs over a restricted range of visual space. However, there have been studies suggesting interactions among motion detectors operating on widely separated spatial regions. To understand these lateral spatial interactions beyond motion pooling regions, we examined the effect of surrounding motion on the direction of the center stimulus under several stimulus conditions. We have found that there is a motion direction shift of the center stimulus caused by surrounding motion depending on its motion direction, spatial proximity to the center stimulus, contrast, speed, and the extent of motion area. This effect was observed both for monocular and dichoptic presentations of the pattern. However, the perceived direction shift decreased when the spatial frequency ratio of the center and surround stimuli varied, or a non-Fourier motion pattern was used for both center and surround stimuli. We present a model consisting of lateral inhibitory interactions between pattern motion unit networks to explain the direction shift observed in the experiments.

Contrast Sensitivity↗
PubMed1999

Global-motion detection with transparent-motion signals.

A number of experiments were conducted to compare the ability of observers to extract unidirectional and bidirectional (transparent) global-motion signals. In the unidirectional condition, the noise signal consisted of purely randomly-moving dots while in the bidirectional condition, a number of the randomly moving dots were replaced by the same number of dots moving in a specific (secondary-signal) direction. The threshold measure was the minimum number of signal dots required to determine the global-motion direction. For the bidirectional condition, parameters varied were the angular separation between the global-motion and secondary-signal directions and the strength of the secondary signal. Thresholds for unidirectional and bidirectional conditions were the same when the angular difference between global-motion and secondary-signal directions were 90 degrees or greater, i.e. the ability of observers to extract a transparent signal was the same as their ability to extract a unidirectional one. Similarly, with motion-in-depth signals, thresholds for extracting a centripetal signal were not elevated by replacing a number of the randomly-moving noise dots with the same number centrifugally-moving dots. The results are interpreted as indicating that motion signals moving between 90 and 180 degrees to the global-motion direction provide uniform masking of the global-motion signal. For angular separations less than 90 degrees, a suprathreshold secondary signal resulted in threshold elevation. This result could be due, to stronger inhibition from motion units tuned to similar (< 90 degrees) directions, broad directional-tuning of the underlying motion units (changing the task from signal detection to a signal discrimination) or a combination of the two.

Depth Perception↗
PubMed1998

The constructive nature of vision: direct evidence from functional magnetic resonance imaging studies of apparent motion and motion imagery.

Echoplanar functional magnetic resonance imaging was used to monitor activation changes of brain areas while subjects viewed apparent motion stimuli and while they were engaged in motion imagery. Human cortical areas MT (V5) and MST were the first areas of the 'dorsal' processing stream which responded with a clear increase in signal intensity to apparent motion stimuli as compared with flickering control conditions. Apparent motion of figures defined by illusory contours evoked greater activation in V2 and MT/MST than appropriate control conditions. Several areas of the dorsal pathway (V3A, MT/MST, areas in the inferior and superior parietal lobule) as well as prefrontal areas including FEF and BA 9/46 responded strongly when subjects merely imagined moving stimuli which they had seen several seconds before. The activation during motion imagery increased with the synaptic distance of an area from V1 along the dorsal processing stream. Area MT/MST was selectively activated during motion imagery but not during a static imagery control condition. The comparison between the results obtained with objective motion, apparent motion and imagined motion provides further insights into a complex cortical network of motion-sensitive areas driven by bottom-up and top-down neural processes.

Adult↗
PubMed1998

Surface discontinuity is critical in a moving observer's perception of objects' depth order and relative motion from retinal image motion.

The visual system perceptually decomposes retinal image motion into three basic components that are ecologically significant for the human observer: object depth, object motion, and self motion. Using this conceptual framework, we explored the relationship between them by examining perception of objects' depth order and relative motion during self motion. We found that the visual system obeyed what we call the parallax-sign constraint, but in different ways depending on whether the retinal image motion contained velocity discontinuity or not. When velocity discontinuity existed (e.g. in dynamic occlusion, transparent motion), the subject perceptually interpreted image motion as relative motion between surfaces with stable depth order. When velocity discontinuity did not exist, he/she perceived depth-order reversal but no relative motion. The results suggest that the existence of surface discontinuity or of multiple surfaces indexed by velocity discontinuity inhibits the reversal of global depth order.

Depth Perception↗
PubMed1999

Motion aftereffect of combined first-order and second-order motion.

When, after prolonged viewing of a moving stimulus, a stationary (test) pattern is presented to an observer, this results in an illusory movement in the direction opposite to the adapting motion. Typically, this motion aftereffect (MAE) does not occur after adaptation to a second-order motion stimulus (i.e. an equiluminous stimulus where the movement is defined by a contrast or texture border, not by a luminance border). However, a MAE of second-order motion is perceived when, instead of a static test pattern, a dynamic test pattern is used. Here, we investigate whether a second-order motion stimulus does affect the MAE on a static test pattern (sMAE), when second-order motion is presented in combination with first-order motion during adaptation. The results show that this is indeed the case. Although the second-order motion stimulus is too weak to produce a convincing sMAE on its own, its influence on the sMAE is of equal strength to that of the first-order motion component, when they are adapted to simultaneously. The results suggest that the perceptual appearance of the sMAE originates from the site where first-order and second-order motion are integrated.

Contrast Sensitivity↗
PubMed2006

Visual motion interferes with tactile motion perception.

Previous studies have demonstrated that visual apparent motion can alter the judgment of auditory apparent motion. We investigated the effect of visual apparent motion on judgments of the direction of tactile apparent motion. When visual motion was presented at the same time as, but in a direction opposite to, tactile motion, accuracy in judging the direction of tactile apparent motion was substantially reduced. This reduction in performance is referred to as 'the congruency effect'. Similar effects were observed when the visual display was placed either near to the tactile display or at some distance from the tactile display (experiment 1). In experiment 2, the relative alignment between the visual and tactile directions of motion was varied. The size of the congruency effect was similar at 0 degrees and 45 degrees alignments but much reduced at a 90 degrees alignment. In experiment 3, subjects made confidence ratings of their judgments of the direction of the tactile motion. The results indicated that the congruency effect was not due to subjects being unsure of the direction of motion and being forced to guess. In experiment 4, static visual stimuli were shown to have no effect on the judgments of direction of the tactile stimuli. The extent to which the congruency effect reflects capture effects and is the result of perceptual versus post-perceptual processes is discussed.

Analysis of Variance↗
PubMed1997

Cervical sagittal range-of-motion analysis using three methods. Cervical range-of-motion device, 3space, and radiography.

STUDY DESIGN: Cervical flexion, extension, protrusion, and retraction were comparatively measured in volunteers using a cervical range-of-motion device (Performance Attainment Associates, Roseville, MN), a 3space system (Polhemus, Colchester, VT), and lateral radiographs. OBJECTIVES: To compare the outcomes of three methods of measurement of cervical flexion, extension, protrusion, and retraction. SUMMARY OF BACKGROUND DATA: Few studies compare cervical range-of-motion measurement devices with radiographic measurements, and no studies have compared methods of measurement for cervical protrusion and retraction measurement. METHODS: In 20 asymptomatic volunteers, four end-range sagittal cervical positions (flexion, extension, protrusion, and retraction) were measured simultaneously using a cervical range-of-motion device, a 3Space and lateral cervical radiographs. Measurements were compared, and differences were analyzed. RESULTS: There were no significant differences for flexion and extension measurements between the cervical range-of-motion device and that radiographic angle determined by an occipital line and the vertical, nor were there any between the 3Space and that radiographic angle between this same occipital line and C7. The cervical range-of-motion device and the 3Space measurements for flexion and extension, however, differed significantly from one another (P < 0.05). For protrusion and retraction, there was no significant difference between the 3Space and radiographic measurements, but these two both differed significantly from the cervical range-of-motion device (P < 0.05). CONCLUSIONS: Available methods of measurement differ as to whether the cervical spine is isolated or includes upper thoracic motion. Protrusion and retraction can be measured reliably with all three methods studied, but without measurement consistency between devices. Because end-range cervical flexion and extension-cannot occur in isolation from upper thoracic motion, true cervical motion can be measured only with an internally referenced, or landmark-based, methodology such as the 3Space. Even though the cervical range-of-motion device cannot measure isolated cervical flexion and extension, it is nevertheless a reliable clinical tool in measuring flexion and extension as well as protrusion and retraction as long as patient thoracic positioning is standardized to minimize the upper thoracic contribution.

Adult↗
PubMed1993

Floating axis does not reduce motion artifacts in a model of left ventricular wall motion in dogs.

Methods of measuring regional wall motion of the left ventricle superimpose end-diastolic and end-systolic images. Differences in dimensions between images are assumed to be due to contraction, but they are also due to motion artifacts. To determine whether the errors caused by motion artifacts are reduced when measured with floating-axis referencing, and whether the measurement method affects these errors, we simulated end-systolic angiograms of a pure contraction (control) and contractions affected by motion artifacts and then measured differences in wall motion between angiograms with hemichord, radial, and trapezoid methods, using floating-axis and fixed-axis referencing. We chose these three methods because they form the basis for other methods, e.g., the center line method. For the simulations, we applied deformation patterns of the left ventricle, computed from the motion of tantalum markers implanted in the endocardiums of six dogs, to end-diastolic angiograms. This marker method measured the myocardial wall motion directly, independent of the angiogram. We found that differences caused by motion artifacts were not significantly reduced when measured with floating-axis referencing in our model. Normalized differences measured by radial and trapezoid methods were not significantly different, but they were significantly smaller than those measured by the hemichord method. We conclude that the axis referencing system has no significant effect on errors caused by motion artifacts in regional wall motion in our model. The measurement method, however, does affect these errors, with the radial and trapezoid methods being superior to the hemichord method.

Animals↗
PubMed2005

Motion adaptation leads to parsimonious encoding of natural optic flow by blowfly motion vision system.

Neurons sensitive to visual motion change their response properties during prolonged motion stimulation. These changes have been interpreted as adaptive and were concluded, for instance, to adjust the sensitivity of the visual motion pathway to velocity changes or to increase the reliability of encoding of motion information. These conclusions are based on experiments with experimenter-designed motion stimuli that differ substantially with respect to their dynamical properties from the optic flow an animal experiences during normal behavior. We analyze for the first time motion adaptation under natural stimulus conditions. The experiments are done on the H1-cell, an identified neuron in the blowfly visual motion pathway that has served in many previous studies as a model system for visual motion computation. We reconstructed optic flow perceived by a blowfly in free flight and used this behaviorally generated optic flow to study motion adaptation. A variety of measures (variability in spike count, response latency, jitter of spike timing) suggests that the coding quality does not improve with prolonged stimulation. However, although the number of spikes decreases considerably during stimulation with natural optic flow, the amount of information that is conveyed stays nearly constant. Thus the information per spike increases, and motion adaptation leads to parsimonious coding without sacrificing the reliability with which behaviorally relevant information is encoded.

Action Potentials↗
PubMed2004

Multiscale motion mapping: a novel computer vision technique for quantitative, objective echocardiographic motion measurement independent of Doppler: first clinical description and validation.

BACKGROUND: Objective, quantitative, segmental noninvasive/bedside measurement of cardiac motion is highly desirable in cardiovascular medicine, but current technology suffers from significant drawbacks, such as subjectivity of conventional echocardiographic reading, angle dependence of tissue Doppler measurements, radiation exposure by computer tomography, and infrastructure requirements in MRI. We hypothesized that computer vision technology could represent a powerful new paradigm for quantification in echocardiography. METHODS AND RESULTS: We present multiscale motion mapping, a novel computer vision technology that is based on mathematical image processing and that exploits echocardiographic information in a fashion similar to the human visual system. It allows Doppler- and border-independent determination of motion and deformation in echocardiograms at arbitrary locations. Correctness of the measurements was documented in synthetic echocardiograms and phantom experiments. Exploratory case studies demonstrated its usefulness in a series of complex motion analyses that included abnormal septal motion and analysis of myocardial twisting. Clinical applicability was shown in a consecutive series of echocardiograms, in which good feasibility, good correlation with expert rating, and good intraobserver and interobserver concordance were documented. Separate assessment of 2D displacement and deformation at the same location was successfully applied to elucidate paradoxical septal motion, a common clinical problem. CONCLUSIONS: This is the first clinical report of multiscale motion mapping, a novel approach to echocardiographic motion quantification. For the first time, full 2D echocardiographic assessment of both motion and deformation is shown to be feasible. Overcoming current limitations, this computer vision-based technique opens a new door to objective analysis of complex heart motion.

Algorithms↗
PubMed2005

Motion sickness symptoms in a ship motion simulator: effects of inside, outside, and no view.

INTRODUCTION: Vehicle motion characteristics differ between air, road, and sea environments, both vestibularly and visually. Effects of vision on motion sickness have been studied before, though less systematically in a naval setting. It is hypothesized that appropriate visual information on self-motion is beneficial in a naval setting and that task performance is likely reduced as sickness increases. METHODS: Using a within-subjects design, 24 subjects were exposed to 30 min of motion in a ship's bridge motion simulator with 3 visual conditions: an Earth-fixed outside view; an inside view that moved with the subjects; and a blindfolded condition. Subjective sickness symptoms and severity were rated repeatedly before, during, and after motion exposure. During the motion, subjects performed a mental task. RESULTS: Though not excessive, sickness was highest in the inside viewing condition, intermediate in the outside viewing condition, and least in the blindfolded condition. The blindfolded condition was equally as bad as the inside viewing condition during the first 5-10 min of motion exposure. The overall temporal increase of sickness during motion was about equal to the decrease during recovery. No effect of sickness on task performance was observed. DISCUSSION: Most sickness in a naval setting is observed when the visual environment moves with the subjects, as has been reported in other environments, such as cars. Only mild sickness, caused by moderate motions, was provoked in this study and was alleviated by the performance task. A non-linear brain mechanism integrating visual and vestibular information may explain why the least sickness was observed when subjects were blindfolded.

Adaptation, Physiological↗
PubMed1999

Recovery of fMRI activation in motion area MT following storage of the motion aftereffect.

We used functional magnetic resonance imaging (fMRI) during storage of the motion aftereffect (MAE) to examine the relationship between motion perception and neural activity in the human cortical motion complex MT+ (including area MT and adjacent motion-selective cortex). MT+ responds not only to physical motion but also to illusory motion, as in the MAE when subjects who have adapted to continuous motion report that a subsequent stationary test stimulus appears to move in the opposite direction. In the phenomenon of storage, the total decay time of the MAE is extended by inserting a dark period between adaptation and test phases. That is, when the static test pattern is presented after a storage period equal in duration to the normal MAE, the illusory motion reappears for almost as long as the original effect despite the delay. We examined fMRI activation in MT+ during and after storage. Seven subjects viewed continuous motion, followed either by an undelayed stationary test (immediate MAE) or by a completely dark storage interval preceding the test (stored MAE). Like the perceptual effect, activity in MT+ dropped during the storage interval then rebounded to reach a level much higher than after the same delay without storage. Although MT+ activity was slightly enhanced during the storage period following adaptation to continuous motion (compared with a control sequence in which the adaptation grating oscillated and no MAE was perceived), this enhancement was much less than that observed during the perceptual phenomenon. These results indicate that following adaptation, activity in MT+ is pronounced only with the presentation of an appropriate visual stimulus, during which the MAE is perceived.

Figural Aftereffect↗
PubMedDate not supplied

Processing of first-order motion in marmoset visual cortex is influenced by second-order motion.

We measured the responses of single neurons in marmoset visual cortex (V1, V2, and the third visual complex) to moving first-order stimuli and to combined first- and second-order stimuli in order to determine whether first-order motion processing was influenced by second-order motion. Beat stimuli were made by summing two gratings of similar spatial frequency, one of which was static and the other was moving. The beat is the product of a moving sinusoidal carrier (first-order motion) and a moving low-frequency contrast envelope (second-order motion). We compared responses to moving first-order gratings alone with responses to beat patterns with first-order and second-order motion in the same direction as each other, or in opposite directions to each other in order to distinguish first-order and second-order direction-selective responses. In the majority (72%, 67/93) of cells (V1 73%, 45/62; V2 70%, 16/23; third visual complex 75%, 6/8), responses to first-order motion were significantly influenced by the addition of a second-order signal. The second-order envelope was more influential when moving in the opposite direction to the first-order stimulus, reducing first-order direction sensitivity in V1, V2, and the third visual complex. We interpret these results as showing that first-order motion processing through early visual cortex is not separate from second-order motion processing; suggesting that both motion signals are processed by the same system.

Action Potentials↗
PubMed2006

Delayed response to animate implied motion in human motion processing areas.

Viewing static photographs of objects in motion evokes higher fMRI activation in the human medial temporal complex (MT+) than looking at similar photographs without this implied motion. As MT+ is traditionally thought to be involved in motion perception (and not in form perception), this finding suggests feedback from object-recognition areas onto MT+. To investigate this hypothesis, we recorded extracranial potentials evoked by the sight of photographs of biological agents with and without implied motion. The difference in potential between responses to pictures with and without implied motion was maximal between 260 and 400 msec after stimulus onset. Source analysis of this difference revealed one bilateral, symmetrical dipole pair in the occipital lobe. This area also showed a response to real motion, but approximately 100 msec earlier than the implied motion response. The longer latency of the implied motion response in comparison to the real motion response is consistent with a feedback projection onto MT+ following object recognition in higher-level temporal areas.

Adult↗