Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “trajectory”

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 289 records · Page 16Linked to original sources
PubMed2006

Effect of previously fixated locations on saccade trajectory during free visual search.

Recent studies have shown that the saccade trajectory often curved away from an object that was previously attended but irrelevant to the current saccade goal. We investigated whether such curved saccades occur during serial visual search, which requires sequential saccades possibly controlled by inhibition to multiple locations. The results show that the saccade trajectories were affected by at least three previous fixations. Furthermore, the effect of the previous fixations on saccade trajectories decreased exponentially with time or the number of intervening saccades. The relationship between the curved saccade trajectory and inhibition of return during serial visual search was discussed.

Adult↗
PubMed2005

Characterizing psychosocial outcome trajectories following seizure surgery.

PURPOSE: We have developed a new approach to characterizing psychosocial outcome after seizure surgery that allows us to identify diverse individual trajectories as well as subgroups of patients with similar outcomes. METHODS: Eighty-nine anterior temporal lobectomy (ATL) patients were recruited through our Seizure Surgery Follow-up and Rehabilitation Program. The Austin CEP Interview was used to measure psychosocial adjustment presurgery, at discharge, and 1, 3, 6, 12, and 24 months postsurgery. Patient outcome trajectories were characterized across this time frame using a profile-focused form of dual clustering that leads to a lattice representation. RESULTS: Two major, distinct outcome subgroups were identified. Fifty-eight percent (58%) of patients reported good outcomes, characterized by improved family dynamics, enhanced vocational and social functioning, and driving by 24 months postsurgery. A range of trajectories led to these outcomes, including the experience of early postoperative adjustment difficulties. In contrast, 31% of patients perceived their outcomes as poor, reporting affective disturbance at 12 months and difficulties discarding sick role behaviors. Early anxiety served as a marker of poor outcomes, while resolution of early anxiety and vocational change at 12 months were indicators of good outcomes at 24 months. The remaining 11% of patients reported minimal adjustment features. CONCLUSIONS: For the majority of patients, seizure surgery gives rise to an evolving process of postoperative adjustment that leads to distinct outcome trajectories. Our approach questions the clinical sensitivity of health-related quality of life measures that average across patients to provide a unitary measure of outcome. Although preliminary, the findings have implications for postoperative treatment, including the identification of markers of longer-term outcomes.

Adaptation, Psychological↗
PubMed2001

Influence of visual distractors on movement trajectory.

In the present study, we explored the influence of a visual distractor on the trajectory of movements made to join two dots. The two dots could be unconnected (D) or connected by a straight (L) or curved line, convex either to the left (LL) or to the right (RL). The connecting line constituted the visual distractor. In Experiment 1, subjects were asked to perform the joining movement as straight as possible. The results showed that hand trajectory moved to the left of the midsagittal axis in LL and to the right in RL, while it was almost straight both in L and D. In Experiment 2, subjects were explicitly required to follow the connecting line during their movements to verify whether, in the previous experiment, they had used curved lines as guide for their movements. An increase of movement time and different hand paths showed that this was not the case. In Experiment 3, subjects were asked to move as straight as possible without vision of their hand. Hand trajectories were shifted to the left in all experimental conditions, but the leftward shift was greater in LL than in all other conditions, and also greater in D and L than in RL. These findings suggest that the visual distractor influenced hand trajectory by attracting subject's attention and competing with target for motor response. It is hypothesized that the attracting influence operated by the distractor was sustained by involuntary attentional mechanisms.

Adult↗
PubMed1983

Molecular dynamics of native protein. I. Computer simulation of trajectories.

The motion of the atoms in the small protein bovine pancreatic trypsin inhibitor has been simulated for about 60 picoseconds using two different potential energy functions. In one known as HHL the hydrogen bond is purely electrostatic, in the other, known as L79, the hydrogen bond is a directional O . . . H interaction. The energy parameters and techniques used to obtain an accurate, well-equilibrated trajectory are described in detail. The trajectories calculated here with either potential are superior to those obtained in previous simulations on the same protein in that they treat hydrogen bonding realistically and remain closer to the native X-ray structure. Comparison of the two trajectories shows that the potential energy parameters have a significant effect on the shift from the X-ray structure, the distribution of (phi, psi) torsion angles, the pattern of hydrogen bonds and the accessible surface area of individual residues. The L79 potential with directional hydrogen bonds is used to simulate a longer 132 picosecond trajectory that is analysed in the accompanying paper.

Animals↗
PubMed1999

Trajectories of condylar points during nonworking side and protrusive movements of the mandible.

STATEMENT OF PROBLEM: During lateral excursive and protrusive jaw movements, condylar points are distant from any instantaneous rotational center. Therefore, it is likely that different condylar points would follow similar trajectories during these movements. PURPOSE: This study evaluated the effect of changes in condylar point location on trajectories of condylar points on the nonworking side and during a protrusive jaw movement and compared these changes with the effects described for open-close and working-side condylar movements in the same group of subjects. METHODS: The movements of 5 clinically determined condylar points were recorded in 44 subjects during a contralateral excursion and during protrusion (7 radiographically determined condylar points in 2 subjects). RESULTS: During any single jaw movement, the trajectory of each condylar point was similar in form and dimension to the other condylar points within that subject. CONCLUSION: Changes in condylar point location had little effect on the trajectories of condylar points on the nonworking side and during protrusive jaw movement.

Adult↗
PubMed1999

Trajectories of condylar points during working-side excursive movements of the mandible.

STATEMENT OF PROBLEM: Trajectories of different condylar points provide different interpretations of condylar movement during open-close jaw movements. Movement of the working-side condyle is often assessed clinically by recording the trajectory of a single arbitrary condylar point. PURPOSE: This study examined the effect of the differences in condylar point location on condylar point movement trajectories during a working-side movement. METHODS: Different points exhibited different trajectories during a single working-side movement in each of 44 subjects. RESULTS: Up to 40% of a point's displacement could be attributed simply to the location of the point. CONCLUSIONS: Interpretation of condylar movement on the working side within a subject depends on the point chosen.

Adult↗
PubMed1997

Trajectories of the human binocular fixation point during conjugate and non-conjugate gaze-shifts.

This paper describes the spatial trajectories of the binocular fixation point (the intersection point of the two lines of sight) during gaze-shifts within a horizontal plane of regard. Gaze was voluntarily shifted between pairs of real, continuously visible LED targets that were either iso-vergent at 5-25 deg convergence (conjugate version saccades) or differed in vergence angle (by 5-20 deg) as well as in direction (by 5-60 deg; combined version and vergence). Orientations of both eyes were recorded by phase detection in a homogeneous magnetic field with scleral sensor coils. "Conjugate" saccades showed an outward-looping, curved trajectory as a result of transient divergence, typically associated with horizontal saccades. These outward loops were disproportionately larger for far than for near targets, due to the non-linear relation between vergence and distance. Transient divergence increased moderately in magnitude and duration when basic vergence increased from 5 to 25 deg. As a result, transient saccadic disparities increased in angular magnitude as targets got close. Increasing tonic vergence did not, however, slow down conjugate saccades, in contrast to the previously described dynamic slowing effects of vergence on version during gaze-shift involving simultaneous vergence and version changes. Convergent and divergent non-conjugate gaze-shifts each had characteristic trajectories; outward loops were much reduced in convergent and virtually absent in divergent movements. The saccadic component of non-conjugate gaze-shifts was preceded by a pre-saccadic vergence component in the direction of the imminent gaze-shift; its magnitude increased systematically with the increase in vergence demand and with the decrease in version demand. For both pre-saccadic convergence and divergence, this pre-saccadic part of the trajectory tended to follow an iso-direction line through the target of origin; directional change did not start until the saccade began. This suggests that for targets that differ in direction as well as distance, control of the vergence and version components of the gaze-shift can be dissociated to some degree. This seems to argue against models of binocular oculomotor control which assume that each eye responds primarily to its own target, and suggests rather that target vergence and target direction may be processed and responded to separately by ocular vergence and version, with a strong interaction between the two oculomotor activities whenever they occur at the same time.

Adult↗
PubMed1997

Predictive smooth pursuit of complex two-dimensional trajectories demonstrated by perturbation responses in monkeys.

Two-dimensional sum-of-sines waveforms were pursued by the eye with very small phase delays compared with visual feedback delays estimated in the same monkeys. Processing delays in making smooth corrections averaged 90 msec after infrequent right-angle perturbations from a circular trajectory. These feedback delays were much larger than component phase delays during pursuit that averaged: 10 msec for sinusoids, 3 msec for circles, 20 msec for sum-of-two-sines trajectories, and 19 msec for sum-of-three-sines trajectories. This suggests that predictive control can play a strong role during tracking for a variety of simple and complex target trajectories.

Animals↗
PubMed1999

Temporal recruitment along the trajectory of moving objects and the perception of position.

The trajectory of a moving object provides information about its velocity, direction and position. This information can be used to enhance the visual system's ability to detect changes in these parameters. We show that the visibility of the trajectory of a moving object influences the perception of its position. This form of temporal recruitment builds up on a long timescale of approximately 500 ms. Temporary occlusion of the trajectory during this time period reduces recruitment, but does not abolish it. Moreover, we found no spatial restrictions on recruitment on the scale of 10 degrees of arc. When the position of objects on trajectories with different degrees of visibility are compared, this recruitment effect causes spatial offsets. This leads to a visual illusion in which the position of moving objects is misperceived.

Attention↗
PubMed1996

TRAJAN: a tool for analyzing trajectories from molecular simulations.

Molecular dynamics simulations of biological systems are notoriously difficult to analyze because of the complexity of the information that contain. We describe a new method for analyzing trajectories from simulations in order to extract important features of the motion. The trajectory of each atom is partitioned into conformation wells, in each of which its motion is assumed to be predominantly harmonic oscillation around an average position. Thus each atom moves anharmonically through a sequence of wells during the trajectory. The movement of atoms between wells, their ellipsoids of motion within each well, and correlations in the motion of atoms are quantified and can be visualized with molecular graphics. The TRAJAN analysis procedure is applicable to trajectories from equilibrium and nonequilibrium simulations and is not restricted to molecular dynamics simulations. Its application is demonstrated for a range of model systems.

Algorithms↗
PubMed1997

pK(a) calculations along a bacteriorhodopsin molecular dynamics trajectory.

Electrostatic calculations of pK(a-values) are reported along a 400 ps molecular dynamics trajectory of bacteriorhodopsin. The sensitivity of calculated pK(a) values to a number of structural factors and factors related to the modelling of the electrostatics are also studied. The results are very sensitive to the choice of internal dielectric constant of the protein (in the interval 2-4). Moreover it is important to include internal water molecules and to average over a long enough portion ( approximately 100 ps) of an equilibrium molecular dynamics trajectory. The internal waters are necessary to get an ion-counter ion complex with the Schiff base and Arg 82 protonated and the aspartic groups (85 and 212) deprotonated. The fluctuations along the MD-trajectory do not change the protonation state of internal residues at neutral pH. However, at other pH values the averaging along a trajectory maybe crucial to get correct protonation states. A relationship is found between the arginine group 82, the aspartic group 85 and the glutamate group 204. Glu 204 is protonated in the ground state but the pK(a) value decreases towards deprotonation when the chromophore isomerizes into the cis state.

Journal Article↗
PubMed2004

Direct dynamics trajectory study of vibrational effects: can polanyi rules be generalized to a polyatomic system?

We present an ab initio direct dynamics trajectory study of the hydrogen abstraction reaction: H2CO+ + CD4 --> H2COD+ + CD3, with methane excited in two different distortion modes (nu4 and nu2). The trajectory simulations were able to reproduce experimental results and for the first time show how vibrational enhancement originates in reaction of small polyatomic species. Roughly equal contributions from two vibrational enhancement mechanisms were found. The "distortion" mechanism correlates the vibrational effects with vibration-induced reactant distortions, and the "velocity" mechanism correlates vibrational effects with vibrational velocities of the constituent atoms. This reaction has a reactant-like transition state and, thus, would correspond to an "early" barrier system in the context of the well-known Polanyi rules for predicting effects of vibration and collision energy. Straightforward application of these rules would predict that vibration should be ineffective in driving reaction, in disagreement with both experiment and trajectory results. Using the trajectories for guidance, we were able to construct a two-dimensional cut through the reaction potential energy surface that does suggest a predictive, Polanyi-type rule.

Journal Article↗
PubMed2005

Trajectory dynamics study of the Ar + CH4 dissociation reaction at high temperatures: the importance of zero-point-energy effects.

Large-scale classical trajectory calculations have been performed to study the reaction Ar + CH4--> CH3 +H + Ar in the temperature range 2500 < or = T/K < or = 4500. The potential energy surface used for ArCH4 is the sum of the nonbonding pairwise potentials of Hase and collaborators (J. Chem. Phys. 2001, 114, 535) that models the intermolecular interaction and the CH4 intramolecular potential of Duchovic et al. (J. Phys. Chem. 1984, 88, 1339), which has been modified to account for the H-H repulsion at small bending angles. The thermal rate coefficient has been calculated, and the zero-point energy (ZPE) of the CH3 product molecule has been taken into account in the analysis of the results; also, two approaches have been applied for discarding predissociative trajectories. In both cases, good agreement is observed between the experimental and trajectory results after imposing the ZPE of CH3. The energy-transfer parameters have also been obtained from trajectory calculations and compared with available values estimated from experiment using the master equation formalism; in general, the agreement is good.

Journal Article↗
PubMed2006

Classical trajectory simulations of photoionization dynamics of tryptophan: intramolecular energy flow, hydrogen-transfer processes and conformational transitions.

One-photon and two-photon ionization dynamics of tryptophan is studied by classical trajectory simulations using the semiempirical parametric method number 3 (PM3) potential surface in "on the fly" calculations. The tryptophan conformer is assumed to be in the vibrational ground state prior to ionization. Initial conditions for the trajectories are weighted according to the Wigner distribution function computed for that state. Vertical ionization in the spirit of the classical Franck-Condon principle is assumed. For the two-photon ionization process the ionization is assumed to go resonantively through the first excited state. Most trajectories are computed, and the analysis is carried out for the first 10 ps. A range of interesting effects are observed. The main findings are as follows: (1) Multiple conformational transitions are observed in most of the trajectories within the ultrafast duration of 10 ps. (2) Hydrogen transfer from the carboxyl group to the amino group and back has been observed. A zwitterion is formed as a transient state. (3) Two new isomers are formed during the dynamics, which have apparently not been previously observed. (4) Fast energy flow between the ring modes and the amino acid backbone is observed for both one- and two-photon ionization. However, the effective vibrational temperatures only approach the same value after 90 ps. The conformation transition dynamics, the proton-transfer processes and the vibrational energy flow are discussed and analyzed.

Computer Simulation↗
PubMed1997

Possible explanations for trajectory curvature in multijoint arm movements.

Although the straightness of hand paths is a widely accepted feature of human multijoint reaching movement, detailed examinations have revealed slight curvatures in some regions of the workspace. This observation raises the question of whether planned trajectories are straight or curved. If they are straight, 3 possible factors can explain the observed curvatures: (a) imperfect control, (b) visual distortion, or (c) interaction between straight virtual trajectories and the dynamics of the arm. Participants instructed to generate straight movement paths produced movements much straighter than those generated spontaneously. Participants generated spontaneously curved trajectories in the frontoparallel plane, where visual distortion is not expected. Electromyograms suggested that participants generated straighter paths without an increase in arm stiffness. These findings argue against the 3 factors. It follows that planned trajectories are likely to be curved.

Adult↗
PubMed2005

Conjoint developmental trajectories of young adult alcohol and tobacco use.

Developmental and etiological advances have set the stage for considering trajectories of problem behavior across the life course, but little work thus far addresses co-occurring problem behavior trajectories. Although recent work characterizes drinking and smoking trajectories, none has explored the course of concurrent drinking and smoking. Using panel data from the Monitoring the Future Project (N=32,087), the authors applied growth mixture modeling to 4 waves of heavy drinking and smoking in a young-adult sample. The authors extracted a single latent group membership factor from heavy drinking and smoking. Associations between trajectory classes and risk factors were relatively unique to the substance being predicted. The association of smoking with alcohol expectancies and delinquency appeared to exist by virtue of smoking's comorbidity with drinking.

Adult↗
PubMed2005

Variation in the drinking trajectories of freshmen college students.

F. K. Del Boca, J. Darkes, P. E. Greenbaum, and M. S. Goldman (2004) examined temporal variations in drinking during the freshmen college year and the relationship of several risk factors to these variations. Here, using the same data, the authors investigate whether a single growth curve adequately characterizes the variability in individual drinking trajectories. Latent growth mixture modeling identified 5 drinking trajectory classes: light-stable, light-stable plus high holiday, medium-increasing, highdecreasing, and heavy-stable. In multivariate predictor analyses, gender (i.e., more women) and lower alcohol expectancies distinguished the light-stable class from other trajectories; only expectancies differentiated the high-decreasing from the heavy-stable and medium-increasing classes. These findings allow for improved identification of individuals at risk for developing problematic trajectories and for development of interventions tailored to specific drinker classes.

Adolescent↗
PubMed2004

The relationship between inhibition of return and saccade trajectory deviations.

After presentation of a peripheral cue, a subsequent saccade to the cued location is delayed (inhibition of return: IOR). Furthermore, saccades typically deviate away from the cued location. The present study examined the relationship between these inhibitory effects. IOR and saccade trajectory deviations were found after central (endogenous) and peripheral (exogenous) cuing of attention, and both effects were larger with an onset cue than with a color singleton cue. However, a dissociation in time course was found between IOR and saccade trajectory deviations. Saccade trajectory deviations occurred at short delays between the cue and the saccade, but IOR was found at longer delays. A model is proposed in which IOR is caused by inhibition applied to a preoculomotor attentional map, whereas saccade trajectory deviations are caused by inhibition applied to the saccade map, in which the final stage of oculomotor programming takes place.

Attention↗