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At least 343 records · Page 19Linked to original sources
PubMed2001

Invisible but common motion in organic crystals: a pedal motion in stilbenes and azobenzenes.

Some molecules that have a molecular skeleton similar to stilbenes and azobenzenes are known to show an orientational disorder in the crystals. Some of the disorders are known to be dynamic and mediated by a pedal motion in crystals. Dynamic processes of (E)-stilbene (1) and (E)-3,3',4,4'-tetramethylazobenzene (2) in the crystals were investigated by X-ray diffraction analyses. The dynamic disorder and the pedal motion were detected at higher temperature, even in the molecules that showed no traces of the disorder at room temperature. The results demonstrated that the pedal motion should always be taken into account, even if no disorder is detected. The reasons for the nonoccurrence of the disorder and for the prevalence of the pedal motion are also discussed.

Journal Article↗
PubMed1993

The role of dynamic three-dimensional trunk motion in occupationally-related low back disorders. The effects of workplace factors, trunk position, and trunk motion characteristics on risk of injury.

Current ergonomic techniques for controlling the risk of occupationally-related low back disorder consist of static assessments of spinal loading during lifting activities. This may be problematic because several biomechanical models and epidemiologic studies suggest that the dynamic characteristics of a lift increase spine loading and the risk of occupational low back disorder. It has been difficult to include this motion information in workplace assessments because the speed at which trunk motion becomes dangerous has not been determined. An in vivo study was performed to assess the contribution of three-dimensional dynamic trunk motions to the risk of low back disorder during occupational lifting in industry. More than 400 repetitive industrial lifting jobs were studied in 48 varied industries. Existing medical and injury records in these industries were examined so that specific jobs historically categorized as either high-risk or low-risk for reported occupationally-related low back disorder could be identified. A triaxial electrogoniometer was worn by workers and documented the three-dimensional angular position, velocity, and acceleration characteristics of the lumbar spine while workers lifted in these high-risk or low-risk jobs. Workplace and individual characteristics were also documented for each of the repetitive lifting tasks. A multiple logistic regression model was developed, based on biomechanical plausibility, and indicated that a combination of five trunk motion and workplace factors distinguished between high and low risk of occupationally-related low back disorder risk well (odds ratio: 10.7). These factors included 1) lifting frequency, 2) load moment, 3) trunk lateral velocity, 4) trunk twisting velocity, and 5) the trunk sagittal angle. This analysis implies that by suitably varying these five factors observed during the lift collectively, the odds of high-risk group membership may decrease by almost 11 times. The predictive power of this model was found to be more than three times greater than that of current lifting guidelines. This study, though not proving causality, indicates an association between the biomechanical factors and low back disorder risk. This model could be used as a quantitative, objective measure to design the workplace so that the risk of occupationally-related low back disorder is minimized.

Biomechanical Phenomena↗
PubMed1999

Backbone dynamics of the human CC chemokine eotaxin: fast motions, slow motions, and implications for receptor binding.

Eotaxin is a member of the chemokine family of about 40 proteins that induce cell migration. Eotaxin binds the CC chemokine receptor CCR3 that is highly expressed by eosinophils, and it is considered important in the pathology of chronic respiratory disorders such as asthma. The high resolution structure of eotaxin is known. The 74 amino acid protein has two disulfide bridges and shows a typical chemokine fold comprised of a core of three antiparallel beta-strands and an overlying alpha-helix. In this paper, we report the backbone dynamics of eotaxin determined through 15N-T1, T2, and [1H]-15N nuclear Overhauser effect heteronuclear multidimensional NMR experiments. This is the first extensive study of the dynamics of a chemokine derived from 600, 500, and 300 MHz NMR field strengths. From the T1, T2, and NOE relaxation data, parameters that describe the internal motions of eotaxin were derived using the Lipari-Szabo model free analysis. The most ordered regions of the protein correspond to the known secondary structure elements. However, surrounding the core, the regions known to be functionally important in chemokines show a range of motions on varying timescales. These include extensive subnanosecond to picosecond motions in the N-terminus, C-terminus, and the N-loop succeeding the disulfides. Analysis of rotational diffusion anisotropy of eotaxin and chemical exchange terms at multiple fields also allowed the confident identification of slow conformational exchange through the "30s" loop, disulfides, and adjacent residues. In addition, we show that these motions may be attenuated in the dimeric form of a synthetic eotaxin. The structure and dynamical basis for eotaxin receptor binding is discussed in light of the dynamics data.

Chemokine CCL11↗
PubMed1984

Interaction between perceived self-motion and object-motion impairs vehicle guidance.

When one is riding in a vehicle, perceptual thresholds for motion of objects are significantly elevated above those determined under corresponding but simulated conditions in the laboratory without concurrent self-motion perception. Authorities on road traffic accidents should thus consider an additional perceptual time of at least 300 milliseconds for detecting critical changes in headway beyond the usual reaction time. Detection times thus corrected consequently lead to an alteration of our conception of safe intervehicle distances in a convoy. This elevation of thresholds for object-motion during self-motion, with its consequences for visual control of vehicle guidance, can be seen as a disadvantageous side effect of an otherwise beneficial space-constancy mechanism, which provides us with a stable world during locomotion.

Automobile Driving↗
PubMed1997

A comparison of two motion analysis systems for the measurement of two-dimensional rearfoot motion during walking.

The purpose of this study was to compare two-dimensional rearfoot motion during walking measured by a traditional video-based motion analysis system to that of an electromagnetic analysis system. Twenty-five individuals (15 men, 10 women) with a mean age of 29.8 years served as subjects for this study. The results of the study showed that there was a high correlation (r = 0.945) between the mean motion paths produced by the two systems, indicating that they were very similar. The electromagnetic motion analysis system was able to produce these similar results in a fraction of the time required by the video-based system.

Adult↗
PubMedDate not supplied

Bodies in motion: monitoring daily activity and exercise with motion sensors in people with chronic pulmonary disease.

A primary goal of pulmonary rehabilitation is to improve health and life quality by encouraging participants to engage in exercise and to increase daily physical activity. The recent advent of motion sensors, including digital pedometers and accelerometers that measure motion as a continuous variable, have added precision to the measurement of free-living daily activity. Daily activity and exercise are variables of keen interest to proponents of the national health agenda, epidemiologists, clinical researchers, and rehabilitation interventionists. This paper summarizes issues related to conceptualizing and monitoring activity in the rehabilitation setting; reviews motion sensor methodology; compares motion-sensing devices; presents analysis issues and current and potential applications to the pulmonary rehabilitation setting; and gives practical applications and limitations.

Exercise↗
PubMed1991

[The relationship between ventilatory lung motion and pulmonary perfusion shown by ventilatory lung motion imaging].

Using ventilatory lung motion imaging, which was obtained from two perfusion lung scintigrams with 99mTc-macroaggregated albumin taken in maximal inspiration and maximal expiration, the lung motion [E-I)/I) of the each unilateral lung was studied in various cardiopulmonary diseases. The sum of (E-I)/I(+) of the unilateral lung showed a decrease in the diseased lung of localized pleuropulmonary diseases, including primary lung cancer and pleural thickening, and in both lungs in cases of heart diseases, diffuse pulmonary diseases including diffuse interstitial pneumonia and diffuse panbronchiolitis. The sum of (E-I)/I(+) of the both lungs, which correlated with vital capacity and PaO2, showed a decrease in diffuse interstitial pneumonia, pulmonary emphysema, diffuse panbronchiolitis, primary lung cancer, pleural diseases and so on. (E-I)/I(+), correlated with pulmonary perfusion (n = 49, r = 0.51, p less than 0.001), but not a few cases showed mismatch, which was observed in primary lung cancer, pleural diseases, pulmonary emphysema, diffuse panbronchiolitis and so on. (E-I)/I(+) better correlated with pulmonary ventilation by ventilation scintigraphy with 81mKr or 133Xe (n = 49, r = 0.61, p less than 0.001) than pulmonary perfusion. The ventilatory lung motion imaging, which demonstrates the motion of the intra-pulmonary areas and lung edges, appears useful for estimating pulmonary ventilation of the perfused area as well as pulmonary perfusion.

Heart Diseases↗
PubMedDate not supplied

Development of computer-directed methods for the identification of hyperactivated motion using motion patterns developed by rabbit sperm during incubation under capacitation conditions.

Rabbit spermatozoa developed motions that mimicked hyperactivated motility during incubation for 16-20 hours under capacitation conditions and in several other commonly used media. Sperm from some rabbits failed to acquire this type of motility, and sperm from others failed to survive the long incubation time. Four motility patterns developed during incubation for 16-20 hours. Motility parameters measured by the CellSoft and CellTrak motion analysis systems were similar except for the average amplitude of lateral head displacement. Multivariate discriminant analysis with complementary regression analysis, and an unrelated tree structured classification method (CART), were used to derive rules, based on motility parameters, for the objective classification of sperm into the two motility classes: 1) nonhyperactivated motility and 2) hyperactivated motility or motility that mimicked hyperactivated motility. The motility parameter wobble (WOB) as superior to the commonly used parameter, linearity, as a classifier of motility types. It classified sperm into the two motility groups with 96.6% efficiency and, together with curvilinear velocity (VCL), attained classification efficiencies of 98%. The classification model produced by CART was preferred over the one obtained by discriminant analysis. The rule for motility classification was dependent on the motion analysis system used to measure the motion parameters. The rule for the CellSoft system, WOB < or = 0.78 and VCL > or = 51 microns/second, classified sperm with an efficiency of 98%, whereas the rule for the CellTrak system, WOB < or = 0.6 and VCL > or = 55 microns/second, achieved a classification efficiency of 97%. These rules should facilitate the study of sperm hyperactivation and its role in sperm function.

Animals↗
PubMed1998

Roll motion stimuli: sensory conflict, perceptual weighting and motion sickness.

In an experiment with 17 subjects, interactions of visual roll motion stimuli and vestibular body tilt stimuli were examined in determining the subjective vertical. Interindividual differences in weighting the visual information were observed, but in general, visual and vestibular responses added in setting the vertical. Despite the conflicting sensory information, motion sickness was not reported apart from one subject on one single occasion. This is in conflict with the sensory mismatch theory on motion sickness, but in agreement with the subjective vertical conflict theory.

Conflict, Psychological↗
PubMed2006

Motion-perception deficits and reading impairment: it's the noise, not the motion.

We tested the hypothesis that deficits on sensory-processing tasks frequently associated with poor reading and dyslexia are the result of impairments in external-noise exclusion, rather than motion perception or magnocellular processing. We compared the motion-direction discrimination thresholds of adults and children with good or poor reading performance, using coherent-motion displays embedded in external noise. Both adults and children who were poor readers had higher thresholds than their respective peers in the presence of high external noise, but not in the presence of low external noise or when the signal was clearly demarcated. Adults' performance in high external noise correlated with their general reading ability, whereas children's performance correlated with their language and verbal abilities. The results support the hypothesis that noise-exclusion deficits impair reading and language development and suggest that the impact of such deficits on the development of reading skills changes with age.

Adolescent↗
PubMed1990

Spatial localization for motion-rejected NMR imaging: SLO-MOTION.

A new method of eliminating NMR image artifacts caused by random or sporadic motion is presented. The method uses only NMR techniques. A combination of a spatial localization method and a standard 2DFT imaging sequence is employed and consequently named SLO-MOTION. Alternatively, the sequence may be used to aid motion artifact reduction by postprocessing methods. The feasibility of the method is demonstrated on a phantom.

Humans↗
PubMed2001

Motion correction algorithms may create spurious brain activations in the absence of subject motion.

This paper describes several experiments that prove that standard motion correction methods may induce spurious activations in some motion-free fMRI studies. This artifact stems from the fact that activated areas behave like biasing outliers for the difference of square-based measures usually driving such registration methods. This effect is demonstrated first using a motion-free simulated time series including artificial activation-like signal changes. Several additional simulations explore the influence of activation amplitude and extent. The effect is finally highlighted on an actual time series obtained from a 3-T magnet. All the experiments are performed using four different realignment methods, which allows us to show that the problem may be overcome by methods based on a robust similarity measure like mutual information.

Algorithms↗
PubMed1984

Coherent global motion percepts from stochastic local motions.

A percept of global, coherent motion results when many different localized motion vectors are combined. We studied the percept with dynamic random dot kinematograms whose elements took independent, random walks of constant step size; their directions of displacement were drawn from a uniform distribution. The tendency to see global, coherent flow along the mean of the uniform distribution varied with the range of the distribution. Psychometric functions were obtained with kinematograms having various step sizes and element densities. The changes in the psychometric function with step size and density are consistent with Ullman's "minimal map theory" of motion correspondence.

Form Perception↗
PubMed1990

Optimal displacement in apparent motion and quadrature models of motion sensing.

A grating appears to move if it is displaced by some amount between two brief presentations, or between multiple successive presentations. A number of recent experiments have examined the influence of displacement size upon either the sensitivity to motion, or upon the induced motion aftereffect. Several recent motion models are based upon quadrature filters that respond in opposite quadrants in the spatiotemporal frequency plane. Predictions of the quadrature model are derived for both two-frame and multiframe displays. Quadrature models generally predict an optimal displacement of 1/4 cycle for two-frame displays, but in the multiframe case the prediction depends entirely on the frame rate.

Humans↗
PubMed2004

Effects of spatial arrangement of visual stimulus on inverted self-motion perception induced by the foreground motion: examination of OKN-suppression hypothesis.

Our previous study revealed that a slowly moving foreground, which is presented in front of a fast-moving orthogonal background, can induce self-motion perception in the same direction as its motion (inverted vection; Vis. Res. 40 (2000) 2915). The present study shows that inverted vection becomes stronger in the conditions where the foreground stimulus is presented in the central area of observer's visual field and the observer's eyes converge on the same depth plane. These stimulus conditions are consistent with the one where the foreground can induce observer's optokinetic nystagmus more effectively, and therefore, the results of this study support our hypothesis in that mis-registered eye-movement information caused by the suppression of optokinetic nystagmus induced by the foreground motion is a critical factor in perceiving inverted vection.

Adult↗
PubMed2005

The motion aftereffect of transparent motion: two temporal channels account for perceived direction.

Adaptation to orthogonal transparent patterns drifting at the same speed produces a unidirectional motion aftereffect (MAE) whose direction is opposite the average adaptation direction. If the patterns move at different speeds, MAE direction can be predicted by an inverse vector average, using the observer's motion sensitivity to each individual pattern as vector magnitudes. These weights are well approximated by the duration of each pattern's MAE, as measured with static test patterns. However, previous efforts to use the inverse-vector-average rule with dynamic test patterns have failed. Generally, these studies have used spatially and temporally broadband test stimuli. Here, in order to gain insight into the possible contribution of temporal channels, we filtered our test pattern in the temporal domain to produce five ideal, octave-width pass-bands. MAE durations were measured for single-component stimuli drifting at various adaptation speeds and tested at a range of temporal frequencies. Then, two components with orthogonal directions and different speeds were combined and the direction of the resulting MAE was measured. The key findings are that: (i) for a given adaptation speed, the duration of a single component's MAE is dependent on test temporal frequency; (ii) the direction of MAEs produced by transparent motion (i.e., bivectorial adaptation) also varies strongly as a function test temporal frequency (by up to 90 degrees for some speed pairings); and (iii) the inverse-vector-average rule predicts the direction of the transparent MAE provided the MAE durations used to weight the vector combination were obtained from stimuli matched in adaptation speed and test temporal frequency. These results are discussed in terms of the number and shape of temporal channels in our visual system.

Adaptation, Physiological↗
PubMed1997

Visual motion perception after brain damage: I. Deficits in global motion perception.

We report on the test results of a group of 32 mostly unilaterally brain-damaged patients examined for global visual motion perception. Three of these patients had severely impaired visual motion perception in their contralateral visual half-field, a deficit remarkably similar to the perceptual defects found in V5-lesioned monkeys. Two of these three patients had a right-hemisphere lesion; the remaining one had a left-hemisphere lesion. We conclude that both hemispheres of the human brain contain an area, functionally equivalent to V5, which subserves visual motion perception in the contralateral visual half-field. Lesion analysis revealed that this area is located in the posterior medial temporal gyrus.

Adult↗
PubMed2002

Fast long-distance interactions in the early processing of motion-defined form and of combinations of motion-defined, luminance-defined, and cyclopean form.

Humans can compare the orientations and locations of two motion-defined test bars several degrees apart so as to rapidly encode and place in memory their mean orientation, orientation difference, separation and mean location, while ignoring stimuli located between the two test bars. Performance is not impaired by randomly varying the location of the bars. We conclude that the two test bars are not compared by shifting gaze location or attention from one test bar to the other, nor by attending to two spatial locations. In addition, observers can discriminate the orientation difference and mean orientation of two test bars that, each of which is rendered visible by a different sub-modality (motion, disparity or luminance). Taking into account the findings reported here and previously reported findings on the early processing of luminance-defined form (Vis. Res. 40 (2000) 2291, Vis. Res. 42 (2002) 49) and cyclopean form (Proc. Roy. Soc. Lond. B 268 (2001) 213) we propose that the human visual system contains a fast long-distance comparator that compares the orientation and locations of two test bars while being insensitive to stimuli in the space between the test bars, and that this process is independent of whether the test bars are rendered visible by only one of three kinds of contrast (luminance, disparity, motion) or by combinations of the three. One role of this comparator mechanism may be to rapidly bind the spatial aspects of the retinal image across sub-modalities immediately after each saccade.

Adult↗