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PubMedDate not supplied

Lumbar motion trends and correlation with low back pain. Part I. A roentgenological evaluation of coupled lumbar motion in lateral bending.

OBJECTIVE: A radiographic study was undertaken to describe the relationship between coupled lumbar motion in lateral bending and the presence of low back pain symptomatology, evaluate trends of coupled motion and determine if these trends were attributable to chance confluence of independent motions. DESIGN: Survey. SETTING: Chiropractic college student health center and private chiropractic clinic. PARTICIPANTS: 249 subjects: 114 with low back pain, 29 asymptomatic with no history and 106 asymptomatic with history. Of these, 194 were freshman volunteers and 55 were new private clinic low back pain patients. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Lumbar segmental coupled motion categories according to the scheme of Cassidy and Grice, as well as a modified scheme. RESULTS: Statistical analysis demonstrated no significant relationship (p = .01) between coupled lumbar motion and low back pain. When viewed intersegmentally, approximately half of all lumbar motion was type II; symmetric motion was rare and attributable to chance confluence of individual segmental motion. CONCLUSIONS: This study suggests that back pain is not an indication for the routine use of lateral bending films for the identification of abnormal coupled motion. Furthermore, each segmental categorization appears to be independent of contralateral categorization as well as motion at all other segmental levels. It is also suggested that type II motion cannot be ruled out as a normal variant. Finally, the ubiquity of coupled motion asymmetry suggests that symmetry must be reevaluated as a criterion for normal spinal function.

Adolescent↗
PubMed1994

Transparent motion perception as detection of unbalanced motion signals. III. Modeling.

In the preceding two companion articles we studied the conditions under which transparent motion perception occurs through psychophysical experiments, and investigated the underlining neural mechanisms through physiological recordings. The main finding of our perceptual experiments was that whenever a display has finely balanced motion signals in all local areas, it is perceptually nontransparent, and that transparent displays always contain motion signals in different directions that are either spatially unbalanced, or unbalanced in their disparity or spatial frequency contents. In the physiological experiments, we found two stages in the processing of transparent stimuli. The first stage is located primarily in area V1. At this stage motion measurements are made and V1 cells respond well to both the balanced, nontransparent stimuli and the unbalanced, perceptually transparent stimuli. The second stage is located primarily in area MT. MT cells show strong suppression between opposite directions of motion. The suppression for the unbalanced, transparent stimuli is significantly less than that for the balanced, nontransparent stimuli. Therefore, the activity in the second, MT stage correlates better with the perception of motion transparency than the first, V1 stage, which does not distinguish reliably between transparent and nontransparent motion. The above experiments suggest a two-stage model of motion perception with a motion measurement stage in V1 and an opponent-direction suppression stage in area MT. In this article we explicitly test this model through analysis and computer simulations, and compare the response of the model to the perceptual and physiological results using the same balanced and unbalanced stimuli we used in the experiments. In the first stage of the computational model, motion energies in different spatial frequency and disparity ranges are extracted from each local region. Similar to V1, this stage does not distinguish between the balanced and unbalanced stimuli. In the subsequent stage motion energies of opposite directions but with same spatial frequency and disparity contents suppress each other using subtractive or divisive inhibition. This stage responds significantly better to the transparent stimuli than to the nontransparent ones, in agreement with MT activity.

Animals↗
PubMed1993

Motion capture changes to induced motion at higher luminance contrasts, smaller eccentricities, and larger inducer sizes.

In the stimulus configuration for "motion capture" phenomenon, we varied luminance contrast of the center disk (target), eccentricity and stimulus size. The subjects had to judge the direction of perceived target motion. We found that motion capture changed to induced motion (the direction of illusory motion was reversed) at smaller eccentricities and larger stimulus sizes. At intermediate eccentricities, motion capture changed to induced motion with increasing luminance contrast of the target. By using magnitude estimation, we also found that even a luminance-defined target was captured ("homochromatic motion capture") and that a moving target was captured by a stationary inducer ("position capture"). Both motion and position capture effects were commonly observed at lower luminance contrasts of the target, larger eccentricities and smaller sizes. From these results, we propose a model of center-surround antagonistic motion contrast detectors in motion processing.

Contrast Sensitivity↗
PubMed1996

Detection thresholds for object motion and self-motion during vestibular and visuo-oculomotor stimulation.

We compared the detection threshold for object motion with that of self-motion in space in healthy human subjects. Stimuli consisted of horizontal rotations of subjects' body with a fixation spot kept in fixed alignment with their heads (vestibular stimulus), rotation of the fixation spot relative to the stationary subjects (visuo-oculomotor stimulus), and a combination thereof by applying rotations of subjects body relative to the stationary object (sinusoidal oscillations, 0.025-0.4 Hz). Two series of experiments were performed. 1) One group of subjects was instructed to attend to, and to indicate the occurrence of, either object or self-motion. 2) A second group was instructed not only to detect the occurrence of a perception, but also to quality it either as object motion or self-motion, depending on which modality dominated perceptually. With either instruction it was found that all three stimulus conditions could evoke both, either an object motion perception or a self-motion perception. The detection thresholds of both perceptions were essentially similar. Thresholds were highest with the vestibular stimulus, intermediate with the stimulus combination, and lowest with the visuo-oculomotor stimulus. The vestibular threshold depended on stimulus frequency, in that it decreased with increasing frequency. Thereby, it became similar to the visuo-oculomotor one, which was essentially constant across frequency. Probability of occurrence of the perceptions in the first experimental series was considerably higher than in the second series, suggesting an important role of attentional mechanisms. In the second series, percent frequency of occurrence of veridical perception (object motion with visuo-oculomotor stimulus, self-motion with stimulus combination) was at chance level (50%) at low stimulus frequency, but was augmented considerably at high frequency. We assume that the latter effect is brought about by a visual-vestibular conflict measure by which the visual stimulus (light spot) is qualified as representing either a moving object or a spatial reference for self-motion. While at suprathreshold stimulus intensities the conflict can determine perception magnitude, at threshold levels its influence is restricted mainly on the probability of occurrence of object and self-motion perception.

Adult↗
PubMed2005

The motion-induced position shift depends on the visual awareness of motion.

Visual motion signals distort the perceived positions of briefly presented stimuli; a briefly-flashed, stationary stimulus appears spatially displaced in the direction of a nearby motion. The present study examined the role of the visual awareness of motion in the motion-induced position shift by using exclusive dominance and suppression of binocular rivalry. Observers dichoptically viewed a flickering radial checkerboard and two sinusoidal gratings that drifted vertically in opposite directions. When observers viewed exclusively either the checkerboard or motion stimulus, two horizontal lines were flashed, one for each side of the rivalry stimulus. During the exclusive dominance of the grating motion, the lines appeared to shift in the directions of the nearby motions. The position shift was identical to that during non-rivalry, monocular viewing of the motion stimulus. However, when the grating motions were completely suppressed, no position shift was observed. These results demonstrate that the motion-induced position shift depends on the visual awareness of motion.

Awareness↗
PubMed1997

Perception of motion direction in luminance- and contrast-defined reversed-phi motion sequences.

Nonlinear processing can be used to recover the motion of contrast modulations of binary noise patterns. A nonlinear stage has also been proposed to explain the perception of forward motion in motion sequences which typically elicit reversed-phi. We examined perceived direction of motion for stimuli in which these reversed motion sequences were used to modulate the contrast of binary noise patterns. A percept of forward motion could be elicted by both luminance-defined and contrast-defined stimuli. The perceived direction of motion seen in the contrast-defined stimuli showed a profound carrier dependency. The replacement of a static carrier by a dynamic carrier can reverse the perceived direction of motion. Forward motion was never seen with dynamic carriers. For luminance- and contrast-defined patterns the reversed motion percept increasingly dominated, with increases in the spatial frequency and temporal frequency of the modulation. Differences in the patterns of responses to the two stimuli over spatial and temporal frequency were abolished by the addition of noise to the luminance-defined stimulus. These data suggest the possibility that a single mechanism may mediate the perception of luminance- and contrast-defined motion.

Contrast Sensitivity↗
PubMed1999

Time course of motion adaptation: motion-onset visual evoked potentials and subjective estimates.

The aim of this study was to quantitatively describe the dynamics of adaptation to visual motion with electrophysiological and psychophysical methods in man. We recorded visual evoked potentials (VEPs) to motion onset of random dot patterns from occipital and occipito-temporal electrodes during a succession of adaptation-recovery sequences. In these sequences the test stimulus was used to set the adaptation level: seven trials with 70% motion duty cycle (adaptation) followed by seven trials of 7% motion duty cycle (recovery). In a similar paradigm we determined the length of the perceptual motion after-effect to obtain a psychophysical measure of the time course of motion adaptation. Our results show a highly significant reduction of the N2 amplitude in the maximally compared to the minimally adapted condition (P < 0.001). Electrophysiological and psychophysical results both indicate that adaptation to visual motion is faster than recovery: The data were fit with an exponential model yielding adaptation and recovery time constants, respectively, of 2.5 and 10.2 s for the N2 amplitude (occipito temporal derivation) and of 7.7 and 16.7 s for the perceptual motion after-effect. Implications for the design of motion stimuli are discussed, e.g. a motion stimulus moving 10% of the time may lead to about 30% motion adaptation.

Adaptation, Ocular↗
PubMed1997

The relative contribution of selected carpal bones to global wrist motion during simulated planar and out-of-plane wrist motion.

The relative contribution of the scaphoid, lunate, triquetrum, and capitate to wrist motion was examined in 6 fresh cadaver forearms. A wrist-joint motion simulator was used to dynamically move each wrist through planar and nonplanar motions. During wrist flexion-extension, the motion of the capitate closely followed the motion of the third metacarpal, while the lunate motion was approximately 50% of the total motion; the triquetrum, 65%, and the scaphoid, 90%. Similar differences in motion for these carpal bones occurred during radioulnar deviation and circumduction and dart-throw motions. This suggests that the scaphoid, lunate, and triquetrum do not normally function as a single unit, but that each bone has an unique arc of motion during global wrist motion.

Biomechanical Phenomena↗
PubMed2003

Detection of nano-second internal motion and determination of overall tumbling times independent of the time scale of internal motion in proteins from NMR relaxation data.

The usual analysis of (15)N relaxation data of proteins is straightforward as long as the assumption can be made that the backbone of most residues only undergoes fast (ps), small amplitude internal motions. If this assumption cannot be made, as for example for proteins which undergo domain motions or for unfolded or partially folded proteins, one needs a method to establish for each residue whether it undergoes fast (ps) or slow (ns) internal motion. Even then it is impossible to determine the correct overall tumbling time, tau(m)(0), via the usual method from the ratio of the longitudinal and transverse relaxation times, if the majority of residues do not undergo fast, small amplitude internal motions. The latter problem is solved when tau(m)(0) can be determined independent of the time scale, tau(i), or the amplitude, S(2), of the internal motion. We propose a new protocol, called PINATA, for analyzing (15)N relaxation data acquired at minimally two field strengths, where no a priori assumption about time scales or amplitude of internal motions needs to be made, and overall tumbling can either be isotropic or anisotropic. The protocol involves four steps. First, for each residue, it is detected whether it undergoes ps- or ns-internal motion, via the combination of the ratio of the longitudinal relaxation time at two fields and the hetero-nuclear NOE. Second, for each residue tau(m)(0) and the exchange broadening, Rex, are iteratively determined. The accuracy of the determination of tau(m)(0) is ca. +/-0.5 ns and of Rex ca +/- 0.7 s(-1), when the relaxation data are of good quality and tau(m)(0)>5 ns, S(2)>0.3, and tau(i)< approximately 3 ns. Third, given tau(m)(0) and Rex, step 1 is repeated to iteratively improve on the internal motion and obtain better estimates of the internal parameter values. Fourth, final time scales and amplitudes for internal motions are determined via grid search based fitting and chi(2)-analysis. The protocol was successfully tested on synthetic and experimental data sets. The synthetic dataset mimics internal motions on either fast or slow time scales, or a combination of both, of either small- or large amplitude, superimposed onto anisotropic overall motion. The procedures are incorporated into MATLAB scripts, which are available on request.

Algorithms↗
PubMed1996

Orthogonal motion after-effect illusion predicted by a model of cortical motion processing.

The motion after-effect occurs after prolonged viewing of motion; a subsequent stationary scene is perceived as moving in the opposite direction. This illusion is thought to arise because motion is represented by the differential activities of populations of cortical neurons tuned to opposite directions; fatigue in one population leads to an imbalance that favours the opposite direction once the stimulus ceases. Following adaptation to multiple directions of motion, the after-effect is unidirectional, indicating that motion signals are integrated across all directions. Yet humans can perceive several directions of motion simultaneously. The question therefore arises as to how the visual system can perform both sharp segregation and global integration of motion signals. Here we show in computer simulations that this can occur if excitatory interactions between different directions are sharply tuned while inhibitory interactions are broadly tuned. Our model predicts that adaptation to simultaneous motion in opposite directions will lead to an orthogonal motion after-effect. This prediction was confirmed in psychophysical experiments. Thus, broadly tuned inhibitory interactions are likely to be important in the integration and segregation of motion signals. These interactions may occur in the cortical area MT, which contains motion-sensitive neurons with properties similar to those required by our model.

Afterimage↗
PubMed2006

A motion phantom study on helical tomotherapy: the dosimetric impacts of delivery technique and motion.

Helical tomotherapy (HT) can potentially be used for lung cancer treatment including stereotactic radiosurgery because of its advanced image guidance and its ability to deliver highly conformal dose distributions. However, previous theoretical and simulation studies reported that the effect of respiratory motion on statically planned tomotherapy treatments may cause substantial differences between the calculated and actual delivered radiation isodose distribution, particularly when the treatment is hypofractionated. In order to determine the dosimetric effects of motion upon actual HT treatment delivery, phantom film dosimetry measurements were performed under static and moving conditions using a clinical HT treatment unit. The motion phantom system was constructed using a programmable motor, a base, a moving platform and a life size lung heterogeneity phantom with wood inserts representing lung tissue with a 3.0 cm diameter spherical tumour density equivalent insert. In order to determine the effects of different motion and tomotherapy delivery parameters, treatment plans were created using jaw sizes of 1.04 cm and 2.47 cm, with incremental gantry rotation periods between the minimum allowed (10 s) and the maximum allowed (60 s). The couch speed varied from 0.009 cm s(-1) to 0.049 cm s(-1), and delivered to a phantom under static and dynamic conditions with peak-to-peak motion amplitudes of 1.2 cm and 2 cm and periods of 3 and 5 s to simulate human respiratory motion of lung tumours. A cylindrical clinical target volume (CTV) was contoured to tightly enclose the tumour insert. 2.0 Gy was prescribed to 95% of the CTV. Two-dimensional dose was measured by a Kodak EDR2 film. Dynamic phantom doses were then quantitatively compared to static phantom doses in terms of axial dose profiles, cumulative dose volume histograms (DVH), percentage of CTV receiving the prescription dose and the minimum dose received by 95% of the CTV. The larger motion amplitude resulted in more under-dosing at the ends of the CTV in the axis of motion, and this effect was greater for the smaller jaw size plans. Due to the size of the penumbra, the 2.47 cm jaw plans provide adequate coverage for smaller amplitudes of motion, +/-0.6 cm in our experiment, without adding any additional margin in the axis of motion to the treatment volume. The periodic heterogeneous patterns described by previous studies were not observed from the single fraction of the phantom measurement. Besides the jaw sizes, CTV dose coverage is not significantly dependent on machine and phantom motion periods. The lack of adverse synchronization patterns from both results validate that HT is a safe technique for treating moving target and hypofractionation.

Equipment Design↗
PubMed2003

Carpal bone kinematics in combined wrist joint motions may differ from the bone kinematics during simple wrist motions.

Present in-vivo carpal kinematic studies have been limited to flexion-extension and radio-ulnar deviation. However these simple motions do not represent the full range of wrist motion employed during activities of daily living. In this study, we investigated combined carpal bone motions for one normal subject. A healthy left wrist from a 48 year old female was CT scanned in three positions: the clinical neutral position of the forearm, the pronated and maximum extended wrist posture, and the supinated and maximum flexed wrist posture. The scans were obtained using a GE8800 scanner at 120 kV and 40 mA. The voxel size was 0.234 mm X0.234 mm X1.0 mm. Principal axes registration methods were used to quantify the carpal bone kinematics. The movement of the carpal bones were described by the means of helical axis parameters. Our subject's carpal bone kinematics in the complex motions differed from the previously studied simple motions. For example, published studies have found that the primary motion of the capitate follows the global motion of the wrist during simple wrist flexion-extension. However, for the complex pronation and extension motion, the capitate rotated ulnarly out of the plane of motion. The only previous study of pisiform motion has shown that during flexion-extension the pisiform moves in the plane of motion. However during pronation and extension, the pisiform rotated ulnarly; while in flexion, the rotation was a combination of flexion and supination.

Carpal Bones↗
PubMed2003

Correlation between normal modes in the 20-200 cm-1 frequency range and localized torsion motions related to certain collective motions in proteins.

In certain biologically relevant collective motions, such as protein domain motions and sub-domain motions, large amplitude movements are localized in one or a few flexible regions consisting of a small number of residues. This paper explores the possible use of normal mode analysis in probing localized vibrational torsion motions in these flexible regions that may be related to certain collective motions. The normal modes of 10 structures of five proteins in different conformation (TRP repressor, calmodulin, calbindin D(9k), HIV-1 protease and troponin C), known to have shear or hinge domain or sub-domain motion, respectively, are analyzed. Our study identifies, for each structure, unique normal modes in the 20-200 cm-1 frequency range, whose corresponding motions are primarily concentrated in the region where large amplitude torsion movements of a known domain or sub-domain motion occur. This suggests possible correlation between normal modes at 20-200 cm-1 frequency range and initial fluctuational motions leading to localized collective motions in proteins, and thus the potential application of normal mode analysis in facilitating the study of biologically important localized motions in biomolecules.

Calbindins↗
PubMed2002

Motion integration during motion aftereffects.

The perceived global motion of a stimulus depends on how its different local motion-direction vectors are distributed in space and time. When they are explicitly co-localized, as in the case of locally paired motion, competitive motion integration mechanisms produce a unitary global motion direction determined by their vector average. During motion aftereffects induced by simultaneous adaptation to multiple motion directions, just as in the case of locally paired motion, different directional signals originate simultaneously from exactly the same position in space. Therefore, the perceived global motion direction during motion aftereffects results from local vector averaging of the co-localized motion-direction signals induced by adaptation.

Journal Article↗
PubMed1994

Transparent motion perception as detection of unbalanced motion signals. I. Psychophysics.

Our visual system can solve the difficult problem of representing multiple motions in the same part of the visual space, the motion transparency problem. We investigated the conditions under which transparent motion perception occurs through psychophysical observations, using a series of visual displays composed of two simple patterns moving in opposite directions. We found that whenever a display has finely balanced opposing motion signals in all local regions, it is perceptually nontransparent. The displays that appeared transparent always contain locally unbalanced motion signals, with some local regions having net motion signals in one direction and some other regions in the opposite direction. These interdigitating net motion signals in both directions appear to be integrated separately to form two overlapping transparent surfaces. Displays that were spatially balanced could be made perceptually transparent if the two components moving in opposite directions were at different stereo depth planes or had different spatial frequency contents. Our results can be explained by proposing a disparity- and spatial frequency-specific suppression stage in the motion pathway, at which motion signals of different directions, but of the same disparity and spatial frequency contents, locally inhibit each other. Such a mechanism would suppress noise input to the motion system, which generally activates several direction channels simultaneously, and would still not eliminate activity evoked by transparent surfaces that are at different depths or have different textures.

Cues↗
PubMed2002

Neural correlates of visual-motion perception as object- or self-motion.

Both self-motion and objects moving in our visual field generate visual motion by displacing images on the retina. Resolving this ambiguity may seem effortless but large-field visual-motion stimuli can yield perceptual rivalry between the real percept of object-motion and the illusory percept of self-motion (vection). We used functional magnetic resonance imaging to record brain activity in human observers exposed to constant-velocity roll-motion. This stimulus induced responses in areas reaching from calcarine to parieto-occipital and to ventral and lateral temporo-occipital cortex and the anterior insula. During vection, early motion-sensitive visual areas and vestibular parieto-insular cortex deactivated, whereas higher-order parieto- and temporo-occipital areas known to respond to optical flow retained identical activity levels. Within this sustained response, these latter areas displayed transient activations in response to each perceptual switch as identified in event-related analyses. Our results thus show that these areas are responsive to the type of visual motion stimulus and highly sensitive to its perceptual bistability. The only region to be more active during perceived self-motion was in, or close to, the cerebellar nodulus. This activation may correspond to the gain increase of torsional optokinetic nystagmus during vection and/or to changes in sensory processing related to the rotational percept. In conclusion, we identified neural correlates of perceiving self-motion from vision alone, i.e., in the absence of confirmatory vestibular or proprioceptive input. These functional properties preserve the organism's ability to move accurately in its environment by relying on visual cues under conditions when the other spatial senses fail to provide such information.

Adult↗
PubMed1995

Restricted ability to recover three-dimensional global motion from one-dimensional motion signals: psychophysical observations.

We tested human ability to recover the 3D structure and motion information from time-varying images where only 1D motion cues were available. Under these conditions, observers exhibit poor performance in discriminating between two perpendicular axes of rotation, or discriminating between rigid and non-rigid 3D motion. This behavior of the visual system is to be contrasted with the good depth from motion performance exhibited when 2D motion cues are given in the image, as was found previously in numerous studies, and also in the work presented here. In a related paper, we suggest a theoretical framework in which to understand this differential performance on the basis of the two types of motion cues (1D vs 2D). Our findings are consistent with those of previous studies of frontoparallel motion, where it was shown that in many cases, the 1D cues alone were not integrated by the visual system into the correct global motion percept. This accumulating evidence suggests that oriented (1D) motion detectors alone cannot account for observed human performance of global motion perception, and that the role of units such as point or endpoint detectors should be studied further.

Cues↗
PubMed1994

Adaptation to second-order motion results in a motion aftereffect for directionally-ambiguous test stimuli.

The magnitude of the motion aftereffect (MAE) obtained following adaptation to first- or second-order motion was measured in two experiments using a nulling method. The second-order motion adaptation stimulus was composed of contrast-modulated noise produced by multiplying two-dimensional random noise by a drifting, 1 c/deg, vertical sine grating. The first-order motion adaptation stimulus was composed of luminance-modulated noise produced by adding, rather than multiplying, the sine grating and noise field. The test stimuli were directionally-ambiguous first- or second-order motion patterns composed of either two oppositely drifting sine gratings added to static noise or its contrast-modulated equivalent. The amplitudes of the two drifting components were manipulated such that as one increased in amplitude the other decreased in amplitude by the same degree. This technique was employed to estimate the null point at which the test no longer appeared to drift in the direction opposite the adaptation direction. In the first experiment all stimuli were equated for visibility by presenting them at the same multiple of threshold and all possible combinations of first- and second-order motion adaptation and test stimuli were examined. The results were similar for all conditions: following adaptation the amplitude of the test component drifting in the same direction as adaptation needed to be approximately twice that of the oppositely drifting component in order to null the perception of unidirectional motion of the test. In a second experiment, the effects of manipulating the amplitude (visibility) of the first- and second-order motion adaptation stimuli on MAE magnitude were investigated. This revealed an approximately linear relationship between MAE magnitude and the amplitudes of the adaptation stimuli. The results demonstrate that, contrary to the findings of several previous studies, adaptation to second-order motion does produce a substantial movement aftereffect. Cross-adaptation between first- and second-order motion stimuli also occurs under appropriate conditions and produces aftereffects that are comparable in magnitude when the stimuli are equated for visibility.

Adaptation, Ocular↗