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.

SourceResearch connectionFrom yearThrough year

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

At least 1,477 records · Page 82Linked to original sources

PubMed2000

Detecting binocular 3D motion in static 3D noise: no effect of viewing distance.

Relative binocular disparity cannot tell us the absolute 3D shape of an object, nor the 3D trajectory of its motion, unless the visual system has independent access to how far away the object is at any moment. Indeed, as the viewing distance is changed, the same disparate retinal motions will correspond to very different real 3D trajectories. In this paper we were interested in whether binocular 3D motion detection is affected by viewing distance. A visual search task was used, in which the observer is asked to detect a target dot, moving in 3D, amidst 3D stationary distractor dots. We found that distance does not affect detection performance. Motion-in-depth is consistently harder to detect than the equivalent lateral motion, for all viewing distances. For a constant retinal motion with both lateral and motion-in-depth components, detection performance is constant despite variations in viewing distance that produce large changes in the direction of the 3D trajectory. We conclude that binocular 3D motion detection relies on retinal, not absolute, visual signals.

Distance Perception↗

PubMed2003

Comparison of sensitivity to first- and second-order local motion in 5-year-olds and adults.

We compared sensitivity to first- versus second-order motion in 5-year-olds and adults tested with stimuli moving at slower (1.5 degrees s(-1)) and faster (6 degrees s(-1)) velocities. Amplitude modulation thresholds were measured for the discrimination of the direction of motion (up vs. down) for luminance-modulated (first-order) and contrast-modulated (second-order) horizontal sine-wave gratings. At the slower velocity (1.5 degrees s(-1)), the differences in threshold between 5-year-olds and adults were small but significant for both first- and second-order stimuli (0.02 and 0.05 log units worse than adults' thresholds, respectively). However, at the faster velocity (6 degrees s(-1)), the differences in threshold between the children and adults were 8 times greater for second-order motion than for first-order motion. Specifically, children's thresholds were 0.16 log units worse than those of adults for second-order motion compared to only 0.02 log units worse for first-order motion. The different pattern of results for first-order and second-order motion at the faster velocity (6 degrees s(-1)) is consistent with models positing different mechanisms for the two types of motion and suggests that those mechanisms mature at different rates.

Adult↗

PubMed1985

Three theories of stroboscopic motion detection.

The three theories derive from three different paradigms. Suprathreshold judgements of perceived quality of motion in multi-flash displays are modelled by space-time Fourier analysis of the motion stimulus. Stroboscopic motion is perceived as being different from real motion to the extent that the additional Fourier components in stroboscopic motion are detectable. Stroboscopic motion of dots along conflicting paths leads to perceptual competition. The theory to describe perceptual I solution derives and proves the uniqueness of strength functions computed only from the time and from the distance between successive points on each path. Time-strength and motion-strength add to determine path-strength; only the strongest path is perceived. Motion-direction detection in continuously drifting two-flash combinations of sinusoidal gratings is described by elaborated Reichardt detectors (ERDs) that compute the covariance of temporal events in two adjacent locations. Other apparently different, detectors that account for direction-detection data are shown to be equivalent to ERDs.

Light↗

PubMed1989

Apparent motion and element connectedness.

Two experiments attempted to determine the effect of the topological property of connectedness on the perception of apparent motion. In Experiment I, direction detection points at subjective equality (PSEs) were measured in a motion competition paradigm. Results indicated that apparent motion was not more likely to be seen between topologically identical elements (e.g., two connected figures) than between elements similar in appearance, but which differed with respect to connectedness. This failed to replicate one finding of Chen (1985). Experiment II tested the possibility that connectedness might affect the quality or visibility of apparent motion. Displacement PSEs for the visibility of motion were measured. Apparent motion between identical figures was significantly more visible than apparent motion between figures similar in appearance, but of different connectedness. These results are discussed in terms of a two-stage model of the long-range motion system.

Humans↗

PubMed1993

The role of early mechanisms in motion transparency and coherence.

Perceptual dissociation of moving plaid patterns into independently moving bar gratings occurs most readily when the grating signals are combined as if the bars were semi-transparent objects (Ramachandran, V. S. (1990) in: AI and the Eye. Wiley, Chichester, pp. 21-77. Stoner, G. R., Albright, T. D. and Ramachandran, V. S. (1990) Nature 344, 153-155). These and other examples of motion transparency are exploited to constrain the set of viable models for human motion processing. For example, one may exclude any fixed recombination of local motion signals into a plaid motion signal. Broad classes of linear and non-linear mechanisms for tracking blobs, corners, and other unambiguous plaid motion cues can also be ruled out because they fail to reproduce the experimental results even qualitatively. The shifting balance between the 'coherent plaid' and 'sliding gratings' percepts are attributed to processing stages before any integration or combination of local motion signals. The first essential stage is a roughly logarithmic nonlinearity before orientation filtering. In general, the resulting cross-products (at the intersections) code unambiguously for the true plaid motion vector, but these signals will be nulled for multiplicatively combined plaid components. Supporting evidence for this idea is obtained in our measurements of detection thresholds for the 'plaid' and 'sliding' percepts. The essential element of the second stage consists of 'end-stop' cells which detect the nullable intersection signal, and so produce a plaid-motion signal with the required characteristics. Finally, it is argued that the ecological role of the proposed mechanism lies in the ability to handle movement of patterned objects in lighting conditions dominated by complicated cast shadows.

Humans↗

PubMed1994

Attention and apparent motion.

Two dissociations between short- and long-range motion in visual search are reported. Previous research has shown parallel processing for short-range motion and apparently serial processing for long-range motion. This finding has been replicated and it has also been found that search for short-range targets can be impaired both by using bicontrast stimuli, and by prior adaptation to the target direction of motion. Neither factor impaired search in long-range motion displays. Adaptation actually facilitated search with long-range displays, which is attributed to response-level effects. A feature-integration account of apparent motion is proposed. In this theory, short-range motion depends on specialized motion feature detectors operating in parallel across the display, but subject to selective adaptation, whereas attention is needed to link successive elements when they appear at greater separations, or across opposite contrasts.

Adaptation, Ocular↗

PubMed2003

Pursuit of the ineffable: perceptual and motor reversals during the tracking of apparent motion.

Pursuit can be guided by perceived rather than physical motion, but the temporal relationship between motion perception and pursuit is unknown. We used an apparent motion stimulus consisting of a horizontal row of evenly spaced Kanizsa illusory squares (1.44 deg2): the illusory contours appeared at the midpoints of the illusory squares presented in the previous frame, producing bi-directional apparent motion of the illusory contours (21.5 deg/s) that could be reversed at will. We measured eye movements in five subjects asked to (1) track the motion of the illusory squares, and (2) reverse the perceived direction while continuing to track the squares. We measured the timing of the voluntary perceptual reversals and compared this to the time course of the reversal in tracking direction. We found that subjects could smoothly track the apparent motion of illusory squares and also produce saccade-free reversals in pursuit velocity. The time course of these motor reversals closely followed the measurements of the perceptual reversal and, on average, the perceptual reversals preceded the pursuit reversals by 53 ms, a delay shorter than when the perceptual reversal was visually guided. Smooth pursuit and the perception of motion direction were in temporal register and highly correlated, suggesting that pursuit can provide a real-time readout for the state of motion perception.

Adult↗

PubMed2003

The extra-retinal motion aftereffect.

Repetitive eye movements are known to produce motion aftereffect (MAE) when made to track a moving stimulus. Explanations typically centre on the retinal motion created in the peripheral visual field by the eye movement. This retinal motion is thought to induce perceived motion in the central test, either through the interaction between peripheral MAE and central target or by adaptation of mechanisms sensitive to the relative motion created between centre and surround. Less attention has been paid to possible extra-retinal contributions to MAE following eye movement. Prolonged eye movement leads to afternystagmus which must be suppressed in order to fixate the stationary test. Chaudhuri (1991, Vision Research, 131, 1639-1645) proposed that nystagmus-suppression gives rise to an extra-retinal motion signal that is incorrectly interpreted as movement of the target. Chaudhuri's demonstration of extra-retinal MAE depended on repeated pursuit to induce the aftereffect. Here we describe conditions for an extra-retinal MAE that follows more reflexive, nystagmus-like eye movement. The MAE is extra-retinal in origin because it occurs in part of the visual field that received no retinal motion stimulation during adaptation. In an explicit test of the nystagmus-suppression hypothesis, we find extra-retinal MAE fails to store over a 30s delay between adaptation and test. Implications for our understanding of motion aftereffects are discussed.

Eye Movements↗

PubMed2003

Depth from motion parallax scales with eye movement gain.

Recent findings suggest that the slow eye movement system, the optokinetic response (OKR) in particular, provides the extra-retinal signal required for the perception of depth from motion parallax (Nawrot, 2003). Considering that both the perception of depth from motion parallax (Ono, Rivest & Ono, 1986; Rivest, Ono & Saida, 1989) and the eye movements made in response to head translations (Schwarz & Miles 1991; Paige, Telford, Seidmen, & Barnes, 1998) appear to scale with viewing distance, changes in perceived depth from motion parallax were studied as a function of viewing distance. If OKR is used in the perception of depth from motion parallax, a change in the OKR signal, caused by a change in viewing distance, should accompany a change in perceived depth from motion parallax. Over a range of viewing distances, binocular stereopsis was used to index perceived depth from motion parallax. At these viewing distances the gain of the OKR portion of the compensatory eye movement was also determined. The results show that the change in OKR gain is mirrored by the change in perceived depth from motion parallax as viewing distance increases. This suggests that the OKR eye movement signal serves an important function in the perception of depth from motion.

Depth Perception↗

PubMed2004

Pattern motion integration in infants.

To investigate the development of motion integration in infants, we used an eye movement technique to measure subjects' ability to track leftward versus rightward pattern motion in a stimulus consisting of a field of spatially segregated moving gratings. Each grating moved in one of two oblique directions, with the two directions interleaved across the display. When spatially integrated, pattern motion for these paired component motions was either rightward or leftward. To control for the possibility that horizontal eye movements elicited by this stimulus were due to the horizontal motion vector present in each obliquely moving grating, we also measured responses to a field where every grating moved in the same oblique direction. The difference in performance between the integration stimulus and this control stimulus was taken as a measure of integration. Data from 2-, 3-, 4-, and 5-month-old infants revealed significant motion integration, suggesting that higher order motion areas, such as the middle temporal area (MT) may develop at a relatively early age. In addition, the integration effect decreased consistently and significantly with age (p <.005), suggesting a reduction in the spatial extent of motion integration over the course of development.

Adult↗

PubMed2004

Prior depth information can bias motion perception.

Previous studies of the motion aperture problem have shown that the direction of grating motion can be biased by using binocular disparity to designate borders of the aperture as intrinsic (belonging to the grating) or extrinsic (resulting from occlusion of the grating). Observers report motion in the direction of the extrinsic border, as if the grating was extended and moving underneath an occluding surface. Here we investigate whether prior information about depth ordering, given by structure-from-motion, can bias the perceived motion direction of a subsequent moving grating in a similar manner. We presented an aperture stimulus that rotated about its vertical and horizontal axes, revealing the depth relationships (intrinsic and extrinsic) of the aperture borders. The grating then translated within the aperture and observers reported the direction of perceived motion. The test stimulus contained no information about the depth ordering of the scene. We found that observers' reported motion shifted toward the direction of the occluding edges, consistent with the intrinsic-extrinsic border predictions. These results indicate that prior scene information, not just depth information explicitly defined in the test stimulus, is used to help solve the motion aperture problem.

Bias↗

PubMed2005

Reference frames in early motion detection.

To perceive the real motion of objects in the world while moving the eyes, retinal motion signals must be compensated by information about eye movements. Here we study when this compensation takes place in the course of visual processing, and whether uncompensated motion signals are ever available. We used a paradigm based on asymmetry in motion detection: Fast-moving objects are found easier among slow-moving distractors than are slow objects among fast distractors. By coupling object motion to eye motion, we created stimuli that moved fast on the retina but slowly in an eye-independent reference frame, or vice versa. In the 100 ms after stimulus onset, motion detection is dominated by retinal motion, uncompensated for eye movements. As early as 130 ms, compensated signals become available: objects that move slowly on the retina but fast in an eye-independent frame are detected as easily as those that move fast on the retina.

Adult↗

PubMed2006

Visual perception of biological motion by form: a template-matching analysis.

Biological motion perception is referred to as the ability to recognize a moving human figure from no more than a few moving point lights. Such point-light stimuli contain limited form information about the shape of the body and local image motion signals from the moving points. The contributions of form and motion to the vivid perception of point-light displays are subject to controversy in the discussion. While some studies claim that local motion signals are critical, others emphasize the role of global form cues. Here, we present a template-matching approach to investigate the role of global form analysis. We used a template-matching method that derives biological motion exclusively from form information. The algorithm used static postures monitored from walking humans as stored templates. We compared the simulation results to psychophysical experiments with the commonly used point-light walker and a variant point-light walker with near-absent local motion signals. The common result in all experiments was a high correlation between simulation results and psychophysical data. The results show that the limited form information in point-light stimuli might be sufficient to perceive biological motion. We suggest that it is possible for humans to extract the sparse form information in point-light walkers and to use it to perceive biological motion by integrating dynamic form information over time.

Discrimination, Psychological↗

PubMed2002

An efficient motion estimation and compensation method for ultrasound synthetic aperture imaging.

This paper describes a method for overcoming motion artifacts in synthetic aperture imaging. The method is based on a computer simulation study on the influence of target motion on synthetic aperture techniques. A region-based motion compensation approach is used in which only the axial motion is estimated and compensated for a given region of interest under the assumption that the whole ROI moves uniformly. The estimated axial motion is calculated with a crosscorrelation method at the point where the focused signal has the maximum energy within the ROI. We also present a method for estimating axial motion using the autocorrelation method that is widely used to estimate average Doppler frequency. Both computer simulations and in vivo experiments show that the proposed crosscorrelation-based method can greatly improve the spatial resolution and SNR of ultrasound imaging by implementing SA techniques for two-way dynamic focusing without motion artifacts. In addition, the autocorrelation-based motion compensation method provides almost the same results as the crosscorrelation-based method, but with a dramatically reduced computational complexity.

Adult↗

PubMed2005

Elbow range of motion in professional baseball pitchers.

BACKGROUND: Physicians involved with the care of baseball players have noted elbow range of motion changes in pitchers. Objective data regarding the extent of these changes have rarely been documented. HYPOTHESIS: Dominant and nondominant elbow range of motion differences are common in baseball pitchers, and these differences are related to player age, amount and length of time professionally pitched, and history of surgical procedures on the dominant extremity. STUDY DESIGN: Cross-sectional study; Level of evidence, 4. METHODS: Thirty-three professional pitchers were evaluated for elbow range of motion during spring training preseason physical examination. Dominant and nondominant elbow range of motion including flexion, extension, supination, and pronation were measured with a goniometer. Range of motion measures from the dominant and nondominant sides were compared. Baseball records were reviewed for arm dominance, age, years of professional pitching, professional innings pitched, and history of elbow surgery. These factors were evaluated for their possible association with range of motion for each side and the difference between sides. RESULTS: Statistically significant differences between dominant and nondominant sides were noted for elbow extension (dominant decreased 7.9 degrees +/- 7.4 degrees, P < .0001), flexion (dominant decreased 5.5 degrees +/- 7.8 degrees, P = .0003), and total flexion-extension arc (dominant decreased 13.3 degrees +/- 13.7 degrees, P < .0001). No significant difference between sides was found for the supination or pronation measures. No correlation was noted for age, pitching history, surgery, or arm dominance and the motion differences. CONCLUSION: Professional pitchers demonstrate elbow flexion and extension differences between dominant and nondominant elbows. No correlation was found between motion differences and age, pitching history, surgery, or arm dominance.

Adult↗

PubMed2006

Tendon healing in a bone tunnel differs at the tunnel entrance versus the tunnel exit: an effect of graft-tunnel motion?

BACKGROUND: Motion between a tendon graft and bone tunnel may impair graft incorporation and lead to tunnel widening. HYPOTHESIS: Healing of a tendon graft in a bone tunnel is inhibited by graft-tunnel motion. STUDY DESIGN: Controlled laboratory study. METHODS: Anterior cruciate ligament reconstruction was performed in 5 cadaveric rabbit limbs, and 3-dimensional graft-tunnel motion was measured using micro-computed tomography. The authors then performed bilateral anterior cruciate ligament reconstruction in 15 rabbits and used histomorphometry to compare tendon-to-bone healing between the tunnel aperture, midtunnel, and tunnel exit and between the anterior and posterior aspects of the tunnel. RESULTS: Graft-tunnel motion was greatest at the tunnel apertures and least at the tunnel exit in cadaveric testing. Healing of the graft was slowest at the tunnel apertures. Tendon-bone interface width was greater at the aperture than at the tunnel exit for the femoral tunnel (P = .04). There was an inverse correlation between time zero graft-tunnel motion and healing in the femoral tunnel (P = .005). There was closer apposition of new bone to the tendon graft in the posterior half of the interface (P < .05). Osteoclasts were found at the tunnel apertures. CONCLUSION: Although graft-tunnel motion was only measured in cadaveric animals, results suggest that healing may be affected by the local mechanical environment, as graft healing in the femoral tunnel was inversely proportional to the magnitude of graft-tunnel motion. CLINICAL RELEVANCE: Graft-tunnel motion may impair early graft incorporation and may lead to osteoclast-mediated bone resorption, contributing to tunnel widening. Early, aggressive postoperative rehabilitation may have detrimental effects on graft-to-bone healing.

Animals↗

PubMedDate not supplied

Loss of motion after anterior cruciate ligament reconstruction.

We did a retrospective review and follow-up examination to investigate the incidence, risk factors, and outcome of patients who developed loss of motion after arthroscopic anterior cruciate ligament reconstruction. Two hundred forty-four patients with a minimum followup of 1 year were reviewed. Loss of motion (defined as a loss of extension of more than 10 degrees or flexion of less than 125 degrees) was identified in 27 patients for an overall incidence of 11.1%. Factors associated with loss of motion included acute reconstruction (less than 1 month from initial injury), male sex, and concomitant medial collateral ligament repair or posterior oblique ligament reefing or both. Twenty-one patients required surgery to regain their motion; three patients required a second procedure. Twenty-one of 27 patients with loss of motion underwent a detailed followup and were compared with 24 randomly chosen controls who had a normal range of motion after anterior cruciate ligament reconstruction. At followup, patients who experienced loss of motion had a significant decrease in noninvolved to involved knee extension and flexion compared to the control patients. There was no difference between our patients and the controls regarding patellofemoral problems, anterior knee laxity, and functional strength. Sixty-seven percent of patients with loss of motion had a good or excellent result in comparison to 80% of the controls.

Adolescent↗

PubMed2003

Failure of cetirizine and fexofenadine to prevent motion sickness.

OBJECTIVE: To determine the effectiveness of 2 second-generation antihistamines in modulating motion sickness induced by Coriolis vestibular cross-coupling stimulation. METHODS: This prospective, randomized, double-blind, crossover, placebo-controlled study was conducted in 18 healthy adults. Subjects were exposed to Coriolis vestibular cross-coupling in the laboratory using the Staircase Profile Test for baseline susceptibility and when under the influence of cetizirine, fexofenadine, and placebo. Subjective evaluation of sickness symptoms was based on the Graybiel diagnostic criteria of acute motion sickness, Golding's scale, and the Coriolis Sickness Susceptibility Index. RESULTS: Repeated measures ANOVA and Friedman nonparametric ANOVA of rank tests revealed that there were significant differences in symptom assessments based on Graybiel's diagnostic criteria (p < or = 0.001), subjective symptoms of motion sickness (p < or = 0.001), and state-anxiety (p < or = 0.001) before and after motion exposure. However, there are no significant differences between the baseline susceptibility to motion sickness and treatment with placebo, cetirizine, or fexofenadine. CONCLUSIONS: The failure of the second-generation antihistamines cetirizine and fexofenadine to prevent motion sickness suggests that the therapeutic actions of this class of antihistamines against motion sickness may be mediated through central versus peripheral receptors. The sedative effect of other antihistamines, such as hydroxyzine, may play a more significant role in alleviating motion sickness than previously thought.

Adult↗