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 919 records · Page 51Linked to original sources
PubMed1987

The representation of nonuniform motion: induced movement.

Induced motion occurs when there is a misallocation of nonuniform motion. Theories of induced motion are reviewed with respect to the model for uniform motion recently proposed by Swanston, Wade, and Day. Theories based on single processes operating at one of the retinocentric, orbitocentric, egocentric, or geocentric levels are not able to account for all aspects of the phenomenon. It is therefore suggested that induced motion is a consequence of combining two different types of motion signals: one provides information by registering the motion with respect to the retina, orbit, and egocentre; the other provides information only on the relational motions between the pattern elements. Simple rules are given for defining a frame of reference for the relational motion process, which can result in a reallocation of the motion signals. It is proposed that the two signals in combination are weighted differentially, with the greater influence coming from the relational signals. Procedures for determining the weighting factors are described, and predictions from the model are examined.

Eye Movements↗
PubMed1995

Visual processing of the motion of an object in three dimensions for a stationary or a moving observer.

A rate of change of relatively disparity is a sufficient binocular stimulus for the perception of motion in depth. For motion within the meridian that contains the eyes, disparity change associated with approaching motion is processed through four channels, each tuned to a different direction of motion in depth. Directional discrimination is most acute but detection sensitivity falls to a minimum for a trajectory passing approximately midway between the eyes. This can be explained if discrimination depends on the relatively of the four channels. Two binocular retinal-image correlates of the direction of the motion of an object in depth are the ratio between the velocities of the retinal images of the object in the left and right eyes [(d phi/dt)R/(d phi/dt)L], and the ratio between the translational velocity of the binocularly fused images and the rates of change of disparity [(d phi/dt)/(d gamma/dt)]. Directional discrimination is possible by using the second cue alone. An isotropic rate of expansion of the retinal image is a sufficient monocular stimulus for the perception of motion in depth. There is no evidence that expansion is processed through channels tuned to the direction of motion in depth. Two monocular correlates of the direction of the motion of an object in depth are the ratio between the translational velocity and the rate of expansion of the retinal image of the object [(d phi/dt)/(d theta/dt)], and the ratio between the velocities of opposite edges of the retinal image [(d alpha 1/dt)/(d alpha 2/dt)]. Subjects are able monocularly to discriminate the direction of motion in depth with high acuity (better than 0.1 deg threshold) in the vertical, horizontal, or oblique meridians, even when the direction and the speed of translational motion are removed as cues. Visual discrimination of time to contact with an approaching object can be disconfounded from discrimination of its rate of expansion and vice versa with a threshold separation ratio of as much as 100:1.

Cues↗
PubMed1997

The motion analogue of the Café Wall illusion.

Detecting visual motion is computationally equivalent to detecting spatiotemporally oriented contours. The question addressed in this study is whether the illusory oriented contour in the space-space domain induces corresponding illusory motion perception. Two experiments were conducted. In experiment 1, the Café Wall pattern, which elicits a strong illusion of orientation (Café Wall illusion), was found to induce an illusion of motion when this pattern was converted to the space-time domain. The strength of the motion illusion depends on the mortar luminance and width, as for the Café Wall illusion. In experiment 2, the adaptation to this illusion of motion was found to induce a motion aftereffect in a static test, which indicates that a first-order-motion system contributes to the induction of the motion illusion. In fact, the motion-energy model was able to predict the strength of this motion aftereffect.

Computers↗
PubMed1998

A computational and perceptual account of motion lines.

To indicate motion in a static drawing, artists often include lines trailing a moving object. The use of these motion lines is notable because they do not seem to be related to anything in the optic array. The dynamic behavior of a neural-network model for contour detection is analyzed and it is shown that it generates trails of oriented responses behind moving stimuli. The properties of the oriented response trails are shown to correspond to motion lines. The model generates trails of different orientations depending on the speed and length of the movement, and thereby predicts different uses of two types of motion lines. The model further predicts that motion lines should bias real motion in some situations. An experiment relating motion lines to ambiguous motion percepts demonstrates that motion lines contribute to motion percepts.

Humans↗
PubMed1998

Aftereffect of high-speed motion.

A visual illusion known as the motion aftereffect is considered to be the perceptual manifestation of motion sensors that are recovering from adaptation. This aftereffect can be obtained for a specific range of adaptation speeds with its magnitude generally peaking for speeds around 3 deg s-1. The classic motion aftereffect is usually measured with a static test pattern. Here, we measured the magnitude of the motion aftereffect for a large range of velocities covering also higher speeds, using both static and dynamic test patterns. The results suggest that at least two (sub)populations of motion-sensitive neurons underlie these motion aftereffects. One population shows itself under static test conditions and is dominant for low adaptation speeds, and the other is prevalent under dynamic test conditions after adaptation to high speeds. The dynamic motion aftereffect can be perceived for adaptation speeds up to three times as fast as the static motion aftereffect. We tested predictions that follow from the hypothesised division in neuronal substrates. We found that for exactly the same adaptation conditions (oppositely directed transparent motion with different speeds), the aftereffect direction differs by 180 degrees depending on the test pattern. The motion aftereffect is opposite to the pattern moving at low speed when the test pattern is static, and opposite to the high-speed pattern for a dynamic test pattern. The determining factor is the combination of adaptation speed and type of test pattern.

Adaptation, Psychological↗
PubMed2001

What does the Ternus display tell us about motion processing in human vision?

The Ternus display is a moving visual stimulus which elicits two very different percepts, according to the length of the interstimulus interval (ISI) between each frame of the motion sequence. These two percepts, referred to as element motion and group motion, have previously been analysed in terms of the operation of a low-level, dedicated short-range motion process (in the case of element motion), and of a higher-level, attentional long-range motion process (in the case of group motion). We used a novel Ternus configuration to show that both element and group motion are, in fact, mediated solely by a process sensitive to changes in the spatial appearance of the Ternus elements. In light of this, it appears that Ternus displays tell us nothing about low-level motion processing, implying that previous studies using Ternus displays, for instance those dealing with dyslexia, require reinterpretation. Further manipulations of the Ternus display revealed that the orientation and spatial-frequency discrimination of the process underlying the analysis of Ternus displays is far worse than thresholds for spatial vision. We conclude that Ternus displays are analysed via a long-range motion, or feature-tracking, process, and that this process is distinct from spatial vision.

Discrimination, Psychological↗
PubMed2002

Motion versus position in the perception of head-centred movement.

Abstract. Observers can recover motion with respect to the head during an eye movement by comparing signals encoding retinal motion and the velocity of pursuit. Evidently there is a mismatch between these signals because perceived head-centred motion is not always veridical. One example is the Filehne illusion, in which a stationary object appears to move in the opposite direction to pursuit. Like the motion aftereffect, the phenomenal experience of the Filehne illusion is one in which the stimulus moves but does not seem to go anywhere. This raises problems when measuring the illusion by motion nulling because the more traditional technique confounds perceived motion with changes in perceived position. We devised a new nulling technique using global-motion stimuli that degraded familiar position cues but preserved cues to motion. Stimuli consisted of random-dot patterns comprising signal and noise dots that moved at the same retinal 'base' speed. Noise moved in random directions. In an eye-stationary speed-matching experiment we found noise slowed perceived retinal speed as 'coherence strength' (ie percentage of signal) was reduced. The effect occurred over the two-octave range of base speeds studied and well above direction threshold. When the same stimuli were combined with pursuit, observers were able to null the Filehne illusion by adjusting coherence. A power law relating coherence to retinal base speed fit the data well with a negative exponent. Eye-movement recordings showed that pursuit was quite accurate. We then tested the hypothesis that the stimuli found at the null-points appeared to move at the same retinal speed. Two observers supported the hypothesis, a third partially, and a fourth showed a small linear trend. In addition, the retinal speed found by the traditional Filehne technique was similar to the matches obtained with the global-motion stimuli. The results provide support for the idea that speed is the critical cue in head-centred motion perception.

Eye Movements↗
PubMed2004

A comparison of auditory and visual apparent motion presented individually and with crossmodal moving distractors.

Unimodal auditory and visual apparent motion (AM) and bimodal audiovisual AM were investigated to determine the effects of crossmodal integration on motion perception and direction-of-motion discrimination in each modality. To determine the optimal stimulus onset asynchrony (SOA) ranges for motion perception and direction discrimination, we initially measured unimodal visual and auditory AMs using one of four durations (50, 100, 200, or 400 ms) and ten SOAs (40-450 ms). In the bimodal conditions, auditory and visual AM were measured in the presence of temporally synchronous, spatially displaced distractors that were either congruent (moving in the same direction) or conflicting (moving in the opposite direction) with respect to target motion. Participants reported whether continuous motion was perceived and its direction. With unimodal auditory and visual AM, motion perception was affected differently by stimulus duration and SOA in the two modalities, while the opposite was observed for direction of motion. In the bimodal audiovisual AM condition, discriminating the direction of motion was affected only in the case of an auditory target. The perceived direction of auditory but not visual AM was reduced to chance levels when the crossmodal distractor direction was conflicting. Conversely, motion perception was unaffected by the distractor direction and, in some cases, the mere presence of a distractor facilitated movement perception.

Acoustic Stimulation↗
PubMed2005

Adaptation to spiral motion in crowding condition.

When a single, moving stimulus is presented in the peripheral visual field, its direction of motion can be easily distinguished, but when the same stimulus is flanked by other similar moving stimuli, observers are unable to report its direction of motion. In this condition, known as 'crowding', specific features of visual stimuli do not access conscious perception. The aim of this study was to investigate whether adaptation to spiral motion is preserved in crowding conditions. Logarithmic spirals were used as adapting stimuli. A rotating spiral stimulus (target spiral) was presented, flanked by spirals of the same type, and observers were adapted to its motion. The observers' task was to report the rotational direction of a directionally ambiguous motion (test stimulus) presented afterwards. The directionally ambiguous motion consisted of a pair of spirals flickering in counterphase, which were mirror images of the target spiral. Although observers were not aware of the rotational direction of the target and identified it at chance levels, the direction of rotation reported by the observers during the test phase (motion aftereffect) was contrarotational to the direction of the adapting spiral. Since all contours of the adapting and test stimuli were 90 degrees apart, local motion detectors tuned to the directions of the mirror-image spiral should fail to respond, and therefore not adapt to the adapting spiral. Thus, any motion aftereffect observed should be attributed to adaptation of global motion detectors (ie rotation detectors). Hence, activation of rotation-selective cells is not necessarily correlated with conscious perception.

Adaptation, Physiological↗
PubMed2006

Stereo motion transparency processing implements an ecological smoothness constraint.

Transparent motion stimuli allow us to investigate how visual motion is processed in the presence of multiple sources of information. We used stereo random-dot kinematograms to determine how motion processing is affected by the difference in direction and depth of two overlapping motion components. Observers judged whether a noise dot display contained one or two directions of motion. For all disparity differences, performance did not change among angles greater than 60 degrees, but the ability to detect transparent motion fell dramatically as the direction difference decreased below 60 degrees. When a disparity difference was added between the two motion components, detection became easier. We compared these results to an ideal-observer model limited by stimulus uncertainty and low-level sources of internal noise. The resulting measure of efficiency--the ratio of human to model performance--reflects changes in how motion stimuli are being processed. A decrease of both the direction and disparity differences had the effect of decreasing efficiency. These results suggest that the mechanism processing transparent motion may implement a smoothness constraint that tends to combine similar motions into a single percept.

Depth Perception↗
PubMed1980

Oligosaccharide motion in erythrocyte membranes investigated by picosecond fluorescence polarization and microsecond dichroism of an optical probe.

Oligosaccharide chains on the surfce of human erythrocytes were labeled with the probe eosin 5-thiosemicarbazide. The probe was conjugated to aldehydes produced by oxidation of sialic acid and galactose residues. The probe is associated mostly with glycophorin A after sialic acid labeling, whereas multiple components, including band 3 and lipids, are labeled after galactose oxidation. Fast molecular motion was studied by measuring steady-state and picosecond time-resolved fluorescence depolarization. Slower motions were investigated by observing flash-induced transient dichroism. It was found that both eosin-labeled sialic acid and galactose residues exhibit a rapid motion with correlation time of approximately 3 nsec. This motion is assigned to independent motion of the probe, possibly in conjunction with a short segment of the oligosaccharide chain. The order parameter of the fast motion is 0.8.-0.9, demonstrating that its angular amplitude is highly restricted. For eosin-labeled sialic acid, the order parameter in the microsecond time range is 0.2-0.3. It is deduced that a second, slower rotational motion is present, which is assigned to a cooperative motion of the oligosaccharide chains. The correlation time of this motion is in the range 10(-7)-(10-5) sec. Some eosin-labeled galactose residues may have a similar slow motion, but most appear to be remarkably immobile over the time range 10(-8)-10(-3) sec.

Eosine Yellowish-(YS)↗
PubMed1997

Multiple developmental pathways for motion processing.

PURPOSE: Image flow across the retina can be classified into several types of motion specifying information about spatial layout and self-movement. Adults process these types of motion via different functional pathways. This article investigates the development of these functional pathways. METHODS: The development of sensitivity to several classes of motion is reviewed and correlated with the neural development of the visual system. RESULTS: Different types of motion processing develop at different rates. The clearest example is that sensitivity to direction of translation shows an earlier onset and a different developmental trajectory than sensitivity to shearing motion. In addition, the onset of sensitivity to translation direction and shearing motion coincides with the development of striate laminae 5/6 and 4B, respectively. This earlier development of the deeper striate laminae is also consistent with reports of neonatal direction discrimination in displays undergoing optical expansion and rotation. CONCLUSIONS: Sensitivity to at least two types of motion, translation and shearing, develop in different ways and continue to be processed differently in adulthood. The differential development of sensitivity to these motion types coincides with the laminar development of striate cortex. It thus follows that the nonuniform development of the motion-processing system must be recognized to assess infant motion sensitivity correctly.

Adult↗
PubMed1999

Random dot motion stimuli are more sensitive than light stimuli for detection of visual field loss in ocular hypertension patients.

PURPOSE: To determine whether motion detection perimetry or luminance size threshold perimetry (a test using the motion perimetry method with luminance stimuli) is more sensitive in detecting visual loss in ocular hypertension patients. METHODS: Motion perimetry uses a customized computer graphics program to detect a subject's ability to identify a coherent shift in position of moving dots in a defined circular area against a background of fixed dots. Motion size threshold is defined as the smallest circular area within which dot motion is detected. Patients respond by touching the area of the computer monitor where they perceive the stimulus with a light pen. The localization errors are measured as the number of pixels from target center for each trial. Luminance size threshold perimetry uses the same technique except the background is dark gray and the stimuli are filled lighter gray circles. We tested one eye in each of 27 ocular hypertension patients and 27 age-matched normal subjects with both tests. Our main outcome measures were motion and luminance size thresholds, total deviation probability plot data, and spatial localization errors. RESULTS: With the total deviation probability plot analysis, the ocular hypertension patients had a greater number of abnormal test locations with motion perimetry stimuli than with luminance stimuli. The abnormal test points were located most often in the superior and inferior nasal regions. Six subjects had nerve fiber bundle-like defects to motion stimuli whereas three patients had defects with luminance size threshold perimetry. The ocular hypertension patients had significantly greater localization errors than the controls with both tests. CONCLUSIONS: Using a size thresholding technique in ocular hypertension patients, random dot motion stimuli appear to be more sensitive than luminance stimuli. Errors in stimulus localization are significantly increased in ocular hypertension patients, independent of the stimulus (motion or luminance) used.

Adult↗
PubMed1994

Comparison of in vivo and in vitro adjacent segment motion after lumbar fusion.

STUDY DESIGN: For in vitro studies, there is no basis for choosing a "load control study" over a "displacement control" study. This study qualitatively compared results from in vitro and in vivo tests, allowing the authors to address the experimental assumptions that in vitro testing contributes to the understanding of the in vivo condition. OBJECTIVES: To compare motion changes at segments adjacent to fusions for in vitro and in vivo tests. SUMMARY OF BACKGROUND DATA: Investigators have measured the effects of spinal fusions on the adjacent segment in a human cadaver model and found greater adjacent facet joint load after fusions. Others have found significant increases in motion and facet loads at segments adjacent to in vitro lumbosacral and long fusions, when the same range of motion was repeated before and after immobilization of lumbar segments. METHODS: L2-L3 motion was measured in vitro by an instrumented spatial linkage under load and displacement control before and after immobilization of segments (L3-L7). In vivo, L2-L3 motion was measured while animals walked on a treadmill. L3-L7 was fused and the L2-L3 motion testing was repeated. The change in in vivo adjacent segment motion was qualitatively compared with the in vitro change under "load" and "displacement" control. RESULTS: Under "load" control, in vitro facet motion did not significantly change after immobilization, whereas under "displacement" control, the facet motion significantly increased from 2.2 +/- 0.4 mm to 4.1 +/- 0.6 mm. Post-instrumentation, in vivo L2-L3 facet motion increased significantly. This change in vivo related better to the changes seen in the in vitro "displacement" control test than to the in vitro "load" control test.

Animals↗
PubMed1998

A motion analysis of the cervical facet joint.

STUDY DESIGN: The stability of motion segments of human cervical spines was sequentially tested as portions of the vertebral anatomy were removed or cut. Isolated, individual facet joints were then similarly studied. OBJECTIVES: To define the laxity of isolated cervical facet joints and the relative contribution of the different components of the vertebral anatomy to the overall stability of the cervical spine. SUMMARY OF BACKGROUND DATA: Facet joints are known to be important in determining cervical stiffness and mobility. This is the first known study in which the biomechanical behavior of isolated cervical facet joints has been documented. METHODS: From five fresh frozen human cervical spines, three C3-C4 and five C5-C6 motion segments were dissected and potted. Rotations and translations in response to 10 bending or twisting moments were recorded by tracking the motion of a testing plate fixed to the superior vertebrae using an articulated arm digitizer. Each motion segment was tested five times, with sequential dissections performed as follows: intact; after removal of the anterior longitudinal ligament intervertebral disc, and posterior longitudinal ligament; after cutting the interspinous ligament; after isolation of the left facet joint; and after isolation of the right facet joint. Each testing sequence involved applying low and high forces 10 cm from the center of the testing plate in each of 10 testing directions. After completion of rotational testing, landmarks on the superior vertebral body and facet joints were digitized to calculate vertebral translations. RESULTS: Isolated facet joints allowed up to 19 degrees of flexion, 14 degrees of extension, 28 degrees of lateral bending, and 17 degrees of rotation. Coupled motions were less in isolated facet joints compared with those in intact vertebral bodies. Isolated facet joints allowed up to 9 mm of translation between superior and inferior surfaces. CONCLUSIONS: Isolated cervical facet joints are highly mobile in comparison with their motions within the constraints of intact motion segments; gliding motions of the isolated facet to near dislocation is possible before the facet capsule constrains motion. Cervical coupled motions are a result of an intact vertebral ring and a combination of the two facet joints. The vertebral ring with facet joints and capsules all intact is necessary for lateral bending stability and rotational stability in the cervical spine.

Aged↗
PubMed2002

Active range of motion utilized in the cervical spine to perform daily functional tasks.

This was a descriptive study to examine active range of motion required in the cervical spine during functional tasks of daily living. The objective of this study was to determine the mean active range of motion of the cervical spine required to perform 13 daily functional tasks. Previous research has examined the absolute ranges of cervical motion for women and men 20-60 years of age; however, no previous study has determined the amount and type of motion that is required for routine activities of daily living. Twenty-eight college-aged students (n = 28) served as healthy subjects and performed three trials of 13 daily tasks of functional activity. The subject's starting position and end range of motion for flexion-extension, rotation, and side bending of each task were observed and recorded using the cervical range of motion device. The three trials were averaged, and ranges of motion across the 28 subjects were reported. Of the 13 daily functional tasks performed, tying shoes (flexion-extension 66.7 degrees), backing up a car (rotation 67.6 degrees), washing hair in the shower (flexion-extension 42.9 degrees), and crossing the street (rotation head left 31.7 degrees and rotation head right 54.3 degrees) required the greatest full active range of motion of the cervical spine. Flexion-extension and rotation of the cervical spine are important to enable functional activity. Four of the 13 daily tasks performed required 30-50% of active range of motion. Side bending was seen to be coupled with rotation in completion of tasks. This article provides a baseline of normal motion of the neck required for activities of daily living and can be used in the assessment of disease states and disability.

Activities of Daily Living↗
PubMedDate not supplied

A comparison of methods for measuring spinal motion in female patients with adolescent idiopathic scoliosis.

Noninvasive surface measures of spine motion are validated in adult patients but are infrequently used in adolescent scoliosis patients. The agreement between surface and radiographic measurements of spinal motion is not known. We performed a comparative prospective analysis of 3 methods to measure spinal motion in female patients with adolescent idiopathic scoliosis (AIS) to establish normative data of spinal motion in AIS patients and evaluate the relationship between surface and radiographic measurements of spine motion. Measurements were obtained using a cloth tape measure, dual inclinometers, and a 3-dimensional electrogoniometer in 37 female patients with AIS. Radiographic parameters of the deformity were correlated with the spine motion. Differences between methods were evaluated by paired t tests. The Bland-Altman method was applied to evaluate agreement in measuring flexion. The average spinal flexion was 5.7 +/- 2.2 cm by the modified Schober method, 49 +/- 11 degrees by the dual inclinometers method, and 64 +/- 10 degrees by the 3-dimensional electrogoniometer. Spinal motion did not vary with magnitude of the scoliosis. In addition, surface measurements of spinal motion did not correlate with radiographic measurements of scoliosis flexibility. In this study, the amount of spinal motion varied, depending on the method of measurement. Surface measurements of motion cannot predict the magnitude or flexibility of the scoliosis.

Adolescent↗
PubMed2005

Defining pseudoarthrosis in the cervical spine with differing motion thresholds.

STUDY DESIGN: Calculate the apparent pseudarthrosis rate for anteriorly plated cervical spine fusions using different threshold levels of intervertebral rotation. OBJECTIVES: Determine whether the apparent pseudarthrosis rate depends on the amount of intervertebral rotation used to characterize a fusion as a pseudarthrosis. SUMMARY OF BACKGROUND DATA: Intervertebral motion at a spine fusion site is an important outcome measure in most spine fusion research studies. Intervertebral motion measures are used to determine if a device can be sold for use in spine fusion surgery. There is no consensus on how much motion is too much motion at a spine fusion site, and the intervertebral motion threshold that is used to define a pseudarthrosis is arbitrary. There are only limited data on the dependence of the pseudarthrosis rate on the threshold used to define a pseudarthrosis. METHODS: Intervertebral motion at the fusion site was measured from flexion extension radiographs taken 1 year after cervical spine fusion using anterior plates and allograft in 200 patients. The number of cases where intervertebral motion at the fusion site exceeded thresholds between 1 degrees and 4 degrees were calculated. RESULTS.: The apparent pseudarthrosis rate varied from 6% when the intervertebral motion threshold was 4 degrees to 44% when the intervertebral motion threshold was 1 degrees . CONCLUSIONS: The apparent pseudarthrosis rate was highly dependent on the threshold of motion used to define a pseudarthrosis.

Bone Plates↗