Head Trajectories Research Articles

Computing and evaluating view-normalized body part trajectories

This paper proposes an approach to compute and evaluate view-normalized body part trajectories of pedestrians from monocular video sequences. The proposed approach uses the 2D trajectories of both feet and of the head extracted from the tracked silhouettes. On that basis, it segments the walking trajectory into piecewise linear segments. Finally, a normalization process is applied to head and feet trajectories over each obtained straight walking segment. View normalization makes head and feet trajectories appear as if seen from a fronto-parallel viewpoint. The latter is assumed to be optimal for gait modeling and identification purposes. The proposed approach is fully automatic as it requires neither manual initialization nor camera calibration. An extensive experimental evaluation of the proposed approach confirms the validity of the normalization process.

Adaptation to cyclic stance perturbations in Parkinson's disease depends on postural demands

The postural reactions of 10 moderate PD patients and 10 age matched controls were studied during stance on a sinusoidally back and forth moving platform during 5 blocks of 10, 1-min trials. Free stance was followed by weight bearing, lowering or raising the center of gravity (COG) by 10%. Next, a book was balanced on the head and finally, forward inclination was constrained. Normal stance strategy, including predictive muscle responses was found during free stance. Modifying COG height caused little response changes. Stance strategy became abnormal when head trajectory or forward inclination was restricted, indicating that ability to generate a nonstandard multi-joint stance strategy, rather than production of adequate stabilizing forces, is impaired in moderate, medicated PD patients.

RECOGNIZING SIMPLE HUMAN ACTIONS USING 3D HEAD MOVEMENT

Recognizing human actions from video has been a challenging problem in computer vision. Although human actions can be inferred from a wide range of data, it has been demonstrated that simple human actions can be inferred by tracking the movement of the head in 2D. This is a promising idea as detecting and tracking the head is expected to be simpler and faster because the head has lower shape variability and higher visibility than other body parts (e.g., hands and/or feet). Although tracking the movement of the head alone does not provide sufficient information for distinguishing among complex human actions, it could serve as a complimentary component of a more sophisticated action recognition system. In this article, we extend this idea by developing a more general, viewpoint invariant, action recognition system by detecting and tracking the 3D position of the head using multiple cameras. The proposed approach employs Principal Component Analysis (PCA) to register the 3D trajectories in a common coordinate system and Dynamic Time Warping (DTW) to align them in time for matching. We present experimental results to demonstrate the potential of using 3D head trajectory information to distinguish among simple but common human actions independently of viewpoint.

Conditions of possible head impacts for standing passengers in public transportation: an experimental study

Standing passenger safety is currently a major challenge for the development of public transportation. One of the current difficulties to overcome this problem is the lack of knowledge about the motion of passengers following a minor incident, e.g. an emergency braking or light collision. This study brings new experimental data about the head kinematics of volunteers in these types of situations. Data were obtained for (1) the three-dimensional head trajectories; (2) the maximal excursions of the head along the longitudinal axis; and (3) corridors of the head tangential velocity versus its longitudinal displacement. Even though there are limitations, these data can be used as a first estimate to predict the risks of impact between the heads of passengers and their surrounding environment. They also provide insight into the impact velocity of this eventual collision. Furthermore, they highlight the influence of the level of perturbation and of the restraint device possibly used.

Uncontrolled manifold analysis of segmental angle variability during walking: preadolescents with and without Down syndrome

The uncontrolled manifold (UCM) approach allows us to address issues concerning the nature of variability. In this study we applied the UCM analysis to gait and to a population known for exhibiting high levels of performance variability, Down syndrome (DS). We wanted to determine if preadolescents (ages between 8 and 10) with DS partition goal-equivalent variability (UCM( ||)) and non-goal equivalent variability differently than peers with typical development (TD) and whether treadmill practice would result in utilizing greater amounts of functional, task-specific variability to accomplish the task goal. We also wanted to determine how variance is structured with respect to two important performance variables: center of mass (COM) and head trajectory at one specific event (i.e., heel contact) for both groups during gait. Preadolescents with and without DS walked on a treadmill below, at, and above their preferred overground speed. We tested both groups before and after four visits of treadmill practice. We found that children with DS partition more UCM( ||) variance than children with TD across all speeds and both pre and post practice. The results also suggest that more segmental configuration variance was structured such that less motion of COM than head position was exhibited at heel contact. Overall, we believe children with DS are employing a different control strategy to compensate for their inherent limitations by exploiting that variability that corresponds to successfully performing the task.

Controlled Metal Detector Mounted on Mine Detection Robot

Landmine detection capability of metal detectors is very sensitive to the gap between buried landmines and the sensor heads. Therefore, human deminers manually scan ground surface with the metal detectors in such a manner that the sensor heads follow the ground surface. In case of robots assisted landmine detection, this function can be performed accurately and safely by controlling the gap and attitude of the sensor heads. In this investigation, the effectiveness of the gap and attitude control of the sensor head by some mechanical manipulator on the landmine detection performance has been addressed quantitatively. To this end, the paper describes the development of a Controlled Metal Detector (CMD) for controlling the gap and attitude of the sensor head. The CMD generates trajectories of the sensor head from the depth information of the ground surface acquired with 3-D stereovision camera in order to avoid any obstacles and possible impact with the ground, and then tracks the trajectories with a trajectory-tracking controller. The effectiveness and the impact related to the gap and attitude control on the landmine detection performance of the CMD have been demonstrated by experimental studies.

Analysis of trajectories of eye, head, and hand movements for early diagnosis of Parkinson’s disease

Relationships between eye, head, and hand movements in patients with stages I-II Parkinson's disease were studied using an original method. The tests for individual movements in patients and healthy individuals yielded similar results, while coordination test revealed significant differences.

Infant eye and head movements toward the side opposite the cue in the anti-saccade paradigm

BackgroundThe anti-saccade task, when people must respond in the direction opposite to a visual stimulus, has been used as a marker of operation of the frontal cortical oculomotor area. However, early development of oculomotor control has been little studied with the infant anti-saccade paradigm, and a few studies did not recognize anti-saccades in infants in light of the results of adult anti-saccade. Since the characteristics of infant eye movements are little known, applying the criteria used in adult study is by no means the best way to study infant anti-saccade. As it is indicated that coordinated eye and head movements often enable infants to control the direction of their gaze, head movements should be examined as an infant orienting response. The aim of this study was to address how infants used eye and head movements during the anti-saccade paradigm. To distinguish infants' responses, we also investigated eye and head movements during a task for an inhibition of return. Inhibition of return, in which delayed responses occur in the direction to which attention had previously been oriented, has been thought to mark activity of the superior colliculus. Since the superior colliculus is thought to develop much earlier in life than the frontal lobes, we thought it useful to compare these task performances during infancy.MethodsInfants were divided into three groups according to age. Anti-saccade and inhibition-of-return tasks were given. Their eye and head movements during tasks were independently recorded by the corneal reflection method in the head-free condition.ResultsYounger infants tended to initiate eye movement less than older ones in both tasks. In the anti-saccade task, responses opposite to the cue tended to show longer latency than responses to the cue. Infants made faster responses toward the side opposite the cue when it was to the right than when it was left of fixation. Regarding the comparison of responses toward the side opposite the cue between two tasks, the leftward eye movement was faster than the leftward head movements in the inhibition-of-return task, while no difference of latency was observed between eye and head movements in the anti-saccade task. A qualitative analysis of the trajectory of these responses revealed that head movement trajectories were steeper in the anti-saccade than in the inhibition-of-return task.ConclusionYounger infants move head and eyes together, with head movements frequently starting first. On the other hand, both the leftward latency difference between eye and head and gentle trajectories of head in inhibition of return indicate that eye movements are more predominant over head movements in the inhibition-of-return task than in the anti-saccade task. This would suggest an earlier developing inhibition-of-return mechanism.

Reliability of the intrinsic and extrinsic patterns of level walking in older women

The aim of the study was to assess short- and long-term reliability of the harmonic analysis of the trajectories of head, upper trunk, and pelvis during walking in healthy older women, which reveals mechanisms to coordinate upper body segments and control head stability in the search for a safer gait. A stereophotogrammetric system was used to measure the displacement of markers located at head, shoulder, and pelvis level in 11 healthy older women (77 ± 2 years) walking on an oval shaped 20-m walkway circuit, in three experimental sessions separated by 6 weeks. The harmonic analysis of the time-curves was highly reliable both within and between sessions (standard error of measurement ranging between 0.15 mm and 1.50 mm for the amplitudes and 0.03 rad and 0.41 rad for the phases) and revealed different oscillatory patterns for the pelvis, head, and upper trunk. An intrinsic pattern, representing the natural overall movement symmetry of the whole population of older women of this study, was described by the first medio-lateral harmonic and second antero-posterior and vertical harmonics. An extrinsic pattern, characteristic of each individual in the population, was described by the first antero-posterior and vertical harmonics. The intrinsic pattern was both intra- and inter-subject repeatable (coefficient of multiple correlation, CMC, ranging between 0.82 and 0.99), while the extrinsic pattern was only intra-subject repeatable (CMC ranging between 0.70 and 0.90). Harmonic analysis reliably describes upper body kinematics in older women for detecting the intrinsic and extrinsic patterns of gait, which reveal fundamental mechanisms governing their walking.

Premotor Correlates of Integrated Feedback Control for Eye–Head Gaze Shifts

Simple activities like picking up the morning newspaper or catching a ball require finely coordinated movements of multiple body segments. How our brain readily achieves such kinematically complex yet remarkably precise multijoint movements remains a fundamental and unresolved question in neuroscience. Many prevailing theoretical frameworks ensure multijoint coordination by means of integrative feedback control. However, to date, it has proven both technically and conceptually difficult to determine whether the activity of motor circuits is consistent with integrated feedback coding. Here, we tested this proposal using coordinated eye-head gaze shifts as an example behavior. Individual neurons in the premotor network that command saccadic eye movements were recorded in monkeys trained to make voluntary eye-head gaze shifts. Head-movement feedback was experimentally controlled by unexpectedly and transiently altering the head trajectory midflight during a subset of movements. We found that the duration and dynamics of neuronal responses were appropriately updated following head perturbations to preserve global movement accuracy. Perturbation-induced increases in gaze shift durations were accompanied by equivalent changes in response durations so that neuronal activity remained tightly synchronized to gaze shift offset. In addition, the saccadic command signal was updated on-line in response to head perturbations applied during gaze shifts. Nearly instantaneous updating of responses, coupled with longer latency changes in overall discharge durations, indicated the convergence of at least two levels of feedback. We propose that this strategy is likely to have analogs in other motor systems and provides the flexibility required for fine-tuning goal-directed movements.

Responses of Collicular Fixation Neurons to Gaze Shift Perturbations in Head-Unrestrained Monkey Reveal Gaze Feedback Control

A prominent hypothesis in motor control is that endpoint errors are minimized because motor commands are updated in real time via internal feedback loops. We investigated in monkey whether orienting saccadic gaze shifts made in the dark with coordinated eye-head movements are controlled by feedback. We recorded from superior colliculus fixation neurons (SCFNs) that fired tonically during fixation and were silent during gaze shifts. When we briefly (<or=700 ms) interrupted gaze shifts by transiently braking head movements, SCFNs fired steadily during brake-induced gaze immobility, and their mean frequency was inversely related to the remaining distance between current gaze position and the target. After head release, a corrective gaze saccade brought gaze on the unseen goal, and SCFN firing frequency peaked. The results support gaze feedback control and show that the SC is part of a network that encodes, during orientation, the distance between eye and target, irrespective of gaze trajectory characteristics.

Targeted Disruption of Tyrosylprotein Sulfotransferase-2, an Enzyme That Catalyzes Post-translational Protein Tyrosine O-Sulfation, Causes Male Infertility

Tyrosine O-sulfation is a post-translational modification mediated by one of two Golgi tyrosylprotein sulfotransferases (TPST-1 and -2) expressed in all mammalian cells. Tyrosine sulfation plays an important role in the function of some known TPST substrates by enhancing protein-protein interactions. To explore the role of these enzymes in vivo and gain insight into other potential TPST substrates, TPST-2-deficient mice were generated by targeted disruption of the Tpst2 gene. Tpst2(+/-) mice appear normal and, when interbred, yield litters of normal size with a Mendelian distribution of the targeted mutation. Tpst2(-/-) mice have moderately delayed growth but appear healthy and attain normal body weight by 10 weeks of age. In contrast to Tpst1(-/-) males that have normal fertility, Tpst2(-/-) males are infertile. Tpst2(-/-) sperm are normal in number, morphology, and motility in normal media and appear to capacitate and undergo acrosomal exocytosis normally. However, they are severely defective in their motility in viscous media and in their ability to fertilize zona pellucida-intact eggs. Adhesion of Tpst2(-/-) sperm to the egg plasma membrane is reduced compared with wild type sperm, but sperm-egg fusion is similar or even increased. These data strongly suggest that tyrosine sulfation of unidentified substrate(s) play a crucial role in these processes and document for the first time the critical importance of post-translational tyrosine sulfation in male fertility.

Head control strategies during whole-body turns

Recent reports have described the motion of individual body segments during turns toward visual targets. During a whole-body turn, the head's trajectory in space is determined by both body-in-space rotation and head-on-body rotation. To inform subsequent investigations of head control strategies during turns, we provide a kinematic description of head and pelvis rotation in 20 healthy human subjects as they performed step turns toward a visible target or in the direction of a previously seen target. At the time of peak head velocity in space, the head was moving faster than the pelvis by approximately 54 degrees s(-1) when turning toward a visible target, and approximately 25 degrees s(-1) when turning in a remembered direction. Peak head velocities were slower in the absence of a visual target, but pelvis velocities were not significantly different. The pattern of relative motion between the head and pelvis followed a temporal sequence. Early in the turn, the head rotated with respect to the pelvis in the same direction as the pelvis was rotating in space. During the mid portions of the turn, en bloc rotation of the head and pelvis predominated. Later in the turn, head-in-space velocity was lower than pelvis-in-space velocity, and was thus relatively stabilized. This pattern of head movement during turns is quite similar to eye-in-head movements during large eye-head gaze shifts. This suggests that in addition to saccadic and stabilization mechanisms, a specific control strategy to move segments together should be incorporated into models of gaze reorienting behavior.

Frontal Impact Dummy Kinematics in Oblique Frontal Collisions: Evaluation Against Post Mortem Human Subject Test Data

Objective. Today, a predominant percentage of vehicles involved in car crashes are exposed to oblique or frontal offset collisions. The aim of this study is to evaluate the 50th percentile male Hybrid III, THOR 99, and THOR Alpha dummies by comparing them with the corresponding kinematics of post mortem human subjects (PMHS) in this type of collision. Methods. The PMHS data include results from oblique frontal collision tests. They include sled tests with near-side and far-side belt geometries at 15°, 30°, and 45° angles. The test subjects were restrained with a three-point lap-shoulder belt and the Δ V was 30 km/h. Results. The results from the Hybrid III and THOR 99 tests showed that, in most of the test, the head trajectories were an average of approximately 0.1 m shorter than those from equivalent PMHS. The Hybrid III and THOR 99 far-side belt geometry tests showed that the belt remained in place longer on the shoulder of the Hybrid III than on the THOR 99 and the THOR Alpha. This was probably due to a stiffer lumbar spine in the Hybrid III and to a large groove in the steel of the superior surface of the Hybrid III shoulder structure. The THOR 99 escaped from the shoulder belt about 40–50 ms earlier than the THOR Alpha. The results from the THOR Alpha tests show that the head trajectory accorded fairly well with the PMHS data, as long as the shoulder belt did not slip off the shoulder. Although the THOR Alpha shoulder escaped the shoulder belt in the 45° far-side belt geometry, the PMHS did not. This may be due to the THOR Alpha shoulder design, with approximately 0.05 m smaller superior and medial shoulder range-of-motion, in combination with a relatively soft lumbar spine. Conclusions. The THOR Alpha provides head trajectories similar to those of the PMHS under these loading conditions, provided the shoulder belt remains in position on the shoulder. When the shoulder belt slipped off the dummy shoulder, the head kinematics was altered. The shoulder range-of-motion may be a contributing factor to the overall kinematics of an occupant in oblique frontal impact situations where the occupant moves in a trajectory at an angle from that of the longitudinal direction of the car.

Paramètres géométriques et mécaniques nécessaires à la reconstruction d'accidents piétons

Le but de ce travail est de mettre en evidence les parametres qui influent sur la trajectoire de la tete lors d'une reconstruction d'accidents pietons en vue d'une meilleure prediction numerique du risque lesionnel. Celle-ci est realisee a partir d'un couplage de modeles multi-corps (pour le pieton) et elements finis (pour la tete et le vehicule).

Head stabilization on a continuously oscillating platform: the effect of a proprioceptive disturbance on the balancing strategy

When standing and balancing on a continuously and predictably moving platform, body equilibrium relies on both anticipatory control and proprioceptive feedback. We have vibrated different postural muscles of the body to assess any effect of confounding the proprioceptive input on balance during such unstable conditions. Low and high platform oscillation frequencies were used, because different strategies are used to withstand the two perturbations. Eyes open (EO) and closed (EC) conditions were also tested, to assess whether the stabilizing effect of vision is independent from the proprioceptive disturbance. Subjects (n = 14) performed two series of trials, EO and EC: (1) quiet erect stance, (2) stance on the platform translating at 0.2 or 0.6 Hz sinusoidally in the anteroposterior (A-P) direction (dynamic conditions). Continuous bilateral vibration (90 Hz) was produced by two vibrators fixed to the following homonymous muscles: dorsal neck, quadriceps, biceps femoris, tibialis anterior, and triceps surae. Acquisition of body segments' displacement began 10 s after the start of platform translation. From markers fixed to head, hip, and malleolus, we computed the A-P oscillation of head and hip, body orientation in space, and cross-correlation (CC) and time-delay between malleolus and head trajectories. The results were (a) the head A-P oscillation was smaller with EO than EC, under both quiet stance and dynamic conditions; (b) vibration of tibialis and triceps surae, but not of other muscles, slightly increased head and body A-P oscillation with EC under dynamic conditions; (c) at 0.2 Hz but not at 0.6 Hz, for all visual and vibration conditions, there was a significant association between head and feet; (d) at 0.2 Hz, EC, neck muscle vibration increased this association, whereas vibration of the other muscles induced a major time delay in the oscillation of head compared with feet; (e) vibration of either neck or tibialis induced forward body leaning, while vibration of either triceps surae or biceps femoris induced backward leaning, with both EO and EC, under both static and dynamic conditions; (f) the head A-P oscillation, however, under dynamic conditions was not dependent on body leaning. The relatively scarce effects of proprioceptive disturbance on head stabilization and multijoint coordination (in spite of effects on body orientation similar to those observed during stance) speak for a major role of anticipatory control in the dynamic equilibrium task. However, the significant vibration-induced time delay in segments' coordination at low translation frequency, EC, suggests that the normally patterned Ia input promotes continuous adjustments of the feed-forward control mode.

Comparison of head- and body-velocity trajectories during locomotion among healthy and vestibulopathic subjects

The optimal strategies for improving locomotor stability in people with vestibulopathy remain unclear. To help identify likely targets for intervention, we sought to determine whether vestibulopathic postural control impairment during locomotor activity was more localized to either the head or the whole body. We used high curvature analysis (HCA) to quantify the smoothness of head- and body-velocity trajectories during repeated stepping in 18 vestibulopathic and 17 healthy subjects. We employed a mixed-model repeated measures analysis of variance to compare differences in head- and body-trajectory HCA scores. Pearson coefficients were used to describe relationships between head- and body-trajectory HCA scores within each group. The results revealed that neither head- nor body-velocity trajectories were relatively more impaired in subjects with vestibulopathy. Importantly, however, the smoothness of head and body trajectories was more strongly related in subjects with vestibulopathy compared with healthy subjects, suggesting that the fundamental motor control impairment produced by vestibulopathy may be related to an abnormal coupling of head and body motion. We discuss implications for locomotor training in patients with vestibulopathy.

Modulation of force transmission to the head while carrying a backpack load at different walking speeds

This study was designed to investigate the capability of the joints and segments to reduce transmission of forces during load carriage. Eleven subjects were required to carry a backpack loaded with 40% of their body weight and to walk at 6 speeds increasing from 0.6 to 1.6 m s −1 in increments of 0.2 m s −1, and then decreasing in the same manner. Subjects were filmed in 3-dimensions, but analysis of shock transmission ratio (TR) was limited to the sagittal plane. Shock transmission was measured as the ratio of peak vertical accelerations (ankle:head, ankle:knee, and knee:head) measured immediately following foot strike. TR for all ratios increased significantly as a function of increasing speed. TR from the ankle to the head showed no significant increase as a function of load carriage, but did increase as a function of load in transmission from knee to head. A significant interaction effect revealed that during load carriage at the higher speeds the acceleration of the ankle and knee decreased below that for the unloaded conditions. These findings suggest that the potentially injurious effects of previously observed increased ground reaction forces and increased joint stiffness while walking with loads are offset by adaptations in the gait pattern that maintain force transmission at acceptable levels. Increased variability in the acceleration of the head and in the transmission ratios suggest a potentially destabilizing effect of load carriage on the head trajectory.

Head–neck finite element model of the crash test dummy THOR

Development, calibration and validation of a three-dimensional finite element model of the head-neck sub-assemblies of the THOR 50th percentile male dummy are presented. The model provides, in conjunction with the use of the physical dummy, a computational tool for head-neck injury studies related to motor vehicle, rail, or aircraft crashes. Physical dummy CAD data is used to construct the finite element mesh. Mass and inertia properties of the model are consistent with those of the hardware. The THOR head spring-cable system, designed to produce a neck that gives more biofidelic head trajectories, is properly represented in the model. Several modelling methods are discussed in detail. The deformable components of the model include head skin (vinyl), face foam (Confor foam), face pad (silicone rubber), head springs, neck cables and neck discs (neoprene rubber). The material properties are determined, or calibrated, mainly from system identifications with data from material tests, head and face impact tests on a full dummy and sled tests on stand-alone head-neck sub-assemblies. The model is validated with the remaining sled test data and head-neck pendulum test data. Key simulation results such as head spring forces, motion trajectories, accelerations at head centre of gravity, and neck forces and moments are compared with the corresponding experimental data, and error analyses are conducted for the presented results.

Intrabolus pressure gradient identifies pathological constriction in the upper esophageal sphincter during flow.

Propulsion of a bolus through the upper esophageal sphincter (UES) is driven by a pressure drop in the direction of flow against frictional resisting force. Basic mechanics suggest that the axial rate of drop in intrabolus pressure (IBP), i.e., the intrabolus pressure gradient (IBPG), should be locally sensitive to abnormal constriction. We sought to quantify space-time patterns of IBP and IBPG that correlate with pathological disruption to transsphincteric bolus transport. High-resolution high-fidelity perfused manometry was applied concurrent with videofluoroscopy in 6 healthy controls and 10 patients with restricted UES opening and 4 bolus volumes. Pressures were interpolated spatially and displayed as space-time isocontours with bolus head and tail trajectories superimposed to identify the IBP domain. IBP and IBPG were averaged over an approximately steady period of transsphincteric flow. The axial location and magnitude of maximum IBPG were quantified for each swallow relative to the location of the abnormal restriction. We found that average hypopharyngeal IBP and locally maximal IBPG were significantly higher in the patient group (P < 0.001), whereas the maximum IBPG was insensitive to bolus volume, and the locations of maximum IBPG in the patient group were well correlated with axial locations of maximal UES constriction (r = 0.84, P < 0.01). Space-time structure of IBP and IBPG correlated qualitatively with swallow dysfunction. Because IBPG reflects pressure force driving the bolus against frictional force in the UES, IBPG reflects local changes in frictional resistance from pathological constriction during bolus flow. Consequently, the location and magnitude of IBPG reflect the existence and location of abnormal constriction, and IBP and IBPG structure reflect decompensation of the pharyngeal swallow.