Obstacle Circumvention Research Articles

Cautious Gait during Navigational Tasks in People with Hemiparesis: An Observational Study.

Locomotor and balance disorders are major limitations for subjects with hemiparesis. The Timed Up and Go (TUG) test is a complex navigational task involving oriented walking and obstacle circumvention. We hypothesized that subjects with hemiparesis adopt a cautious gait during complex locomotor tasks. The primary aim was to compare spatio-temporal gait parameters, indicators of cautious gait, between the locomotor subtasks of the TUG (Go, Turn, Return) and a Straight-line walk in people with hemiparesis. Our secondary aim was to analyze the relationships between TUG performance and balance measures, compare spatio-temporal gait parameters between fallers and non-fallers, and identify the biomechanical determinants of TUG performance. Biomechanical parameters during the TUG and Straight-line walk were analyzed using a motion capture system. A repeated measures ANOVA and two stepwise ascending multiple regressions (with performance variables and biomechanical variables) were conducted. Gait speed, step length, and % single support phase (SSP) of the 29 participants were reduced during Turn compared to Go and Return and the Straight-line walk, and step width and % double support phase were increased. TUG performance was related to several balance measures. Turn performance (R2 = 63%) and Turn trajectory deviation followed by % SSP on the paretic side and the vertical center of mass velocity during Go (R2 = 71%) determined TUG performance time. People with hemiparesis adopt a cautious gait during complex navigation at the expense of performance.

A Survey of Needle Steering Approaches in Minimally Invasive Surgery.

In virtue of a curved insertion path inside tissues, needle steering techniques have revealed the potential with the assistance of medical robots and images. The superiority of this technique has been preliminarily verified with several maneuvers: target realignment, obstacle circumvention, and multi-target access. However, the momentum of needle steering approaches in the past decade leads to an open question-"How to choose an applicable needle steering approach for a specific clinical application?" This survey discusses this question in terms of design choices and clinical considerations, respectively. In view of design choices, this survey proposes a hierarchical taxonomy of current needle steering approaches. Needle steering approaches of different manipulations and designs are classified to systematically review the design choices and their influences on clinical treatments. In view of clinical consideration, this survey discusses the steerability and acceptability of the current needle steering approaches. On this basis, the pros and cons of the current needle steering approaches are weighed and their suitable applications are summarized. At last, this survey concluded with an outlook of the needle steering techniques, including the potential clinical applications and future developments in mechanical design.

An Optimal-Path-Planning Method for Unmanned Surface Vehicles Based on a Novel Group Intelligence Algorithm

Path planning is crucial for unmanned surface vehicles (USVs) to navigate and avoid obstacles efficiently. This study evaluates and contrasts various USV path-planning algorithms, focusing on their effectiveness in dynamic obstacle avoidance, resistance to water currents, and path smoothness. Meanwhile, this research introduces a novel collective intelligence algorithm tailored for two-dimensional environments, integrating dynamic obstacle avoidance and smooth path optimization. The approach tackles the global-path-planning challenge, specifically accounting for moving obstacles and current influences. The algorithm adeptly combines strategies for dynamic obstacle circumvention with an eight-directional current resistance approach, ensuring locally optimal paths that minimize the impact of currents on navigation. Additionally, advanced artificial bee colony algorithms were used during the research process to enhance the method and improve the smoothness of the generated path. Simulation results have verified the superiority of the algorithm in improving the quality of USV path planning. Compared with traditional bee colony algorithms, the improved algorithm increased the length of the optimization path by 8%, shortened the optimization time by 50%, and achieved almost 100% avoidance of dynamic obstacles.

About the Use of Gearless Electric Motors in the Construction of an Exoskeleton Walking on an Uneven Surface

The regular walking (up or down) on a ladder (or an inclined plane) of a human operator with an exoskeleton of the lower extremities, carrying an additional load, is considered. It is assumed that the exoskeleton is equipped with high— torque electric motors without gearboxes — in the knee and, perhaps, in other joints. The modes of flat, single-support quasi-comfortable walking are considered, in the implementation of which both electric motors and a human operator with experience working with this mechanism participate. The nominal pattern of movement associated, in particular, with the circumvention of obstacles (steps) with a portable foot and placing it in the support position at the next step is set and supported by a person. The task of the algorithm controlling electric motors is to partially reduce the load that falls on the operator. From the point of view of minimizing human energy consumption, the supporting leg and especially its knee joint are the most important. In the knee joint of the supporting leg, an algorithm for controlling the corresponding electric motor is proposed, based on measuring the vertical reaction force of the support in combination, perhaps, with the angle in the knee and angular velocity. Feedback is constructed, the "successful" values of the coefficients of which can be predicted using a kind of least squares method along the nominal mode. The task of this feedback is actually the distribution of the load that falls to the share of the operator and the system of electric motors. It is shown by using numerical research methods to what benefits in terms of energy consumption in one regular step this can, in principle, lead. This principle of feedback construction extends further to the hip and ankle moments of the supporting leg. It is assumed that the portable leg is controlled everywhere only by the human operator’s own efforts, the absence of gearboxes allows this to be done without much friction loss, which in turn affects the smallness of energy costs and for the operator.

Algorithm Selection and Application for Robot Path Planning Problems

This article primarily delves into the investigation of robotic path planning in the presence of obstacles, aiming to ascertain optimal traversal routes. It conducts a thorough categorization and discussion of two critical aspects: the ascertainability of the overall map and the regularity of obstacles. In addressing this inquiry, two obstacle scenarios, namely regular and irregular, are posited. The article scrutinizes the path planning and obstacle circumvention techniques for both scenarios. Regarding regular obstacles, a comparative assessment of the A* algorithm, Floyd’s algorithm, and Dijkstra’s algorithm was conducted, culminating in the selection of the A* algorithm for its superior efficiency. For irregular obstacles, the article proposes a pre-processing approach involving the utilization of Matlab’s iterative pixel point traversal to assess obstacle proportions within nodes, subsequently converting irregular obstacles into a regularized format. To summarize, in scenarios with a known overall map, the article advocates employing the A* algorithm for proficient path planning. In situations where the map is undisclosed but obstacles exhibit regularity, the D* algorithm is recommended. For instances involving irregular obstacles and an undisclosed map, a dynamic method for handling newly incorporated nodes into the map is proposed. This article presents tailored solutions for robotic path planning across diverse conditions, offering concise yet effective problem-solving strategies. In conclusion, this study offers a comprehensive array of solutions for robot path planning in obstructed environments, enabling the selection of apt methodologies based on varying conditions and exigencies.

Advanced 3D Navigation System for AGV in Complex Smart Factory Environments

The advancement of Industry 4.0 has significantly propelled the widespread application of automated guided vehicle (AGV) systems within smart factories. As the structural diversity and complexity of smart factories escalate, the conventional two-dimensional plan-based navigation systems with fixed routes have become inadequate. Addressing this challenge, we devised a novel mobile robot navigation system encompassing foundational control, map construction positioning, and autonomous navigation functionalities. Initially, employing point cloud matching algorithms facilitated the construction of a three-dimensional point cloud map within indoor environments, subsequently converted into a navigational two-dimensional grid map. Simultaneously, the utilization of a multi-threaded normal distribution transform (NDT) algorithm enabled precise robot localization in three-dimensional settings. Leveraging grid maps and the robot’s inherent localization data, the A* algorithm was utilized for global path planning. Moreover, building upon the global path, the timed elastic band (TEB) algorithm was employed to establish a kinematic model, crucial for local obstacle avoidance planning. This research substantiated its findings through simulated experiments and real vehicle deployments: Mobile robots scanned environmental data via laser radar and constructing point clouds and grid maps. This facilitated centimeter-level localization and successful circumvention of static obstacles, while simultaneously charting optimal paths to bypass dynamic hindrances. The devised navigation system demonstrated commendable autonomous navigation capabilities. Experimental evidence showcased satisfactory accuracy in practical applications, with positioning errors of 3.6 cm along the x-axis, 3.3 cm along the y-axis, and 4.3° in orientation. This innovation stands to substantially alleviate the low navigation precision and sluggishness encountered by AGV vehicles within intricate smart factory environments, promising a favorable prospect for practical applications.

The effect of whole body vibration on gait stability in individuals with Parkinson's disease: a preliminary study

Background/Aims Whole body vibration could benefit functional mobility in people with Parkinson's disease. A preliminary study was undertaken to analyse the acute effect of whole body vibration on unobstructed walking and obstacle circumvention in people with Parkinson's disease. Methods People with Parkinson's disease and typically healthy individuals as matched controls were divided into four groups with nine individuals in each: experimental or placebo for people with Parkinson's disease and experimental or placebo for the control group. The participants were evaluated in two different gait conditions: unobstructed walking and obstacle circumvention. Then the participants undertook a session of whole body vibration on a KIKOS P201 lateral vibratory platform in two positions: feet shoulder-width apart, and feet shoulder-width apart with slightly flexed knees. The participants were re-evaluated after this session. Results After whole body vibration, those in the experimental Parkinson's disease group had a reduced co-contraction of the tibialis anterior and the gastrocnemius lateralis muscles during unobstructed walking, whereas the co-contraction of the tibialis anterior and the gastrocnemius lateralis muscles increased in the experimental control group. In addition, those in the experimental control group had reduced stride duration in unobstructed walking and in obstacle circumvention. After the placebo intervention, the co-contraction of the tibialis anterior and the gastrocnemius lateralis muscles increased in all conditions and stride duration was reduced in unobstructed walking. Conclusions Although whole body vibration had no acute efficiency on gait (unobstructed walking and obstacle circumvention), it can improve other components, such as strength, which could be important for people with Parkinson's disease.

A dense obstacle avoidance algorithm for UAVs based on safe flight corridor

Aiming at the problem of autonomous obstacle avoidance of fixed-wing UAVs in a complex, dense and multi-obstacle environment, a path planning algorithm for fixed-wing UAVs based on a safe flight corridor is proposed. The difficulty of avoiding dense obstacles lies in the choice of obstacle circumvention and traversal: although circumvention is safer, the flight cost is greater; although the traversal cost is lower, the safety threat is higher. How to quickly solve the optimal path is the core issue. This paper firstly defines a safe flight corridor innovatively based on the maneuvering characteristics of fixed-wing UAVs and the Dubins curves. By comprehensively considering UAV flight safety and flight costs, an obstacle threat evaluation function is constructed. Secondly, in view of the computational complexity caused by the dense obstacles, an obstacle clustering algorithm based on obstacle density is proposed, and the nonlinear evaluation function in a high dynamic environment is quickly approximated by Monte Carlo sampling method. Finally, simulations verify the effectiveness of the proposed algorithm in solving dense obstacle avoidance for fixed-wing UAVs.

Acute unilateral vestibular neuritis contributes to alterations in vestibular function modulating circumvention around obstacles: A pilot study suggesting a role for vestibular signals in the spatial perception of orientation during circumvention.

Walking among crowds avoiding colliding with people is described by patients with vestibular disorders as vertigo-inducing. Accurate body motion while circumventing an impeding obstacle in the gait pathway is dependent on an integration of multimodal sensory cues. However, a direct role of vestibular signals in spatial perception of distance or orientation during obstacle circumvention has not been investigated to date. We examined trunk yaw motion during circumvention in patients with acute unilateral vestibular loss (aUVL) and compared their results with age-matched healthy controls (HCs). Subjects performed five gait tasks with eyes open two times: walk 6 m in total, but after 3 m, circumvent to the left or right, as closely as possible, a cylindrical obstacle representing a person, and then veer back to the original path; walk 6 m, but after left and right circumvention at 3 m, veer, respectively, to the right, and left 45 deg; and walk 6 m without circumvention. Trunk yaw angular velocities (YAVs) were measured using a gyroscope system. Yaw angular velocity peak amplitudes approaching to, and departing from, the circumvented object were always greater for patients with aUVL compared to HCs, regardless of whether passing was to the aUVLs' deficit or normal side. The departing peak YAV was always greater, circa 52 and 87%, than the approaching YAV for HCs when going straight and veering 45 deg (p ≤ 0.0006), respectively. For patients with aUVL, departing velocities were marginally greater (12%) than approaching YAVs when going straight (p < 0.05) and were only 40% greater when veering 45 deg (p = 0.05). The differences in departing YAVs resulted in significantly lower trajectory-end yaw angles for veering trials to the deficit side in patients with aUVL (34 vs. 43 degs in HCs). The results demonstrate the effects of vestibular loss on yaw velocity control during the three phases of circumvention. First, approaching an obstacle, a greater YAV is found in patients with aUVL. Second, the departing YAV is found to be less than in HCs with respect to the approaching velocity, resulting in larger deficit side passing yaw angles. Third, patients with UVLs show yaw errors returning to the desired trajectory. These results could provide a basis for rehabilitation protocols helping to avoid collisions while walking in crowded spaces.

Dual tasking reduces gait asymmetry of trajectory deviation during obstacle circumvention in people with Parkinson's disease.

Certain aspects of gait may depend on cognition, and the effects of dual-tasking (DT) on gait asymmetry (GA) during obstacle circumvention in people with Parkinson's disease (pwPD) may be walking phase-dependent. While the approaching phase requires allocating significant cognitive resources to perform the task, outweighing the available resources may increase GA. During the avoiding phase, the obstacle could be used as an external cue, enhancing the attention to the obstacle and, consequently, improving gait control and regulating GA. The study investigated the effects of obstacle circumvention during gait with DT on GA in pwPD, considering the circumvention phase. Thirty participants, 15 pwPD and 15 neurologically healthy individuals, circumvented an obstacle 20 times (in total) according to side (right and left side) and DT (presence and absence). Spatial-temporal stride parameters, medial-lateral and horizontal trajectory deviations from the original path, strategy to obstacle circumvention (lead limb away from or close to the obstacle during the crossing step), and gaze parameters were calculated during the approaching and avoiding phases. The parameters were grouped considering the side that the obstacle was circumvented during each task, and the symmetry index was calculated. The results showed greater asymmetry of time of fixations, width, duration, and velocity during the approaching phase (p<0.02), whereas the avoiding phase decreased asymmetry of medial-lateral and horizontal trajectory deviations parameters (p<0.001) during obstacle circumvention with DT, in both pwPD and control group. The findings offer a basis for considering that goal-directed movement control may regulate GA in pwPD.

A global path planning algorithm based on the feature map

The feature map is a characteristic of high computational efficiency, but it is seldom used in path planning due to its lack of expression of environmental details. To solve this problem, a global path planning algorithm based on the feature map is proposed based on the directionality of line segment features. First, the robot searches the path along the direction of the target position but turns to search in the direction parallel to the obstacle, which it approaches until the line between the robot and the target position does not intersect with obstacles. Then it turns to the target position, keep searching the path. Meanwhile, the problems of the direction selection of turning point, corner point and obstacle circumvention in the searching process are analysed and corresponding solutions are put forth. Finally, a path optimisation algorithm with variable parameters is proposed, making the optimised path shorter and smoother. Simulation experiments demonstrate that the proposed algorithm is superior to A* algorithm in terms of computation time and path length, especially of the computation efficiency.

The starting distance of obstacle circumvention did not affect intersegmental coordination in individuals with Parkinson's disease.

Obstacle circumvention is a challenging task in Parkinson's disease (PD). Body segments adjustments, such as changing the direction of the trunk, followed by a change in the direction of the head, and modifications in the positioning of the feet, are necessary to circumvent an obstacle during walking. For that, individuals need to identify the distance to the obstacle, its characteristics (such as its dimension), and perform well-coordinated movements. However, PD is characterized by rigidity, which may be increased in the axial axis and compromise the task execution. Also, worsening sensory integration in PD may increase the time to perform these body segments adjustments, thus impairing the movement coordination when starting obstacle circumvention near to the obstacle. To determine if the starting distance (1.5m, 3m, or 5m) from the obstacle could modify the intersegmental coordination (specifically, the coordination between head, trunk, and pelvis) during the obstacle circumvention steps in individuals with PD. Fourteen individuals with a diagnosis of idiopathic PD and 15 neurologically healthy individuals (CG) from the community were included in this study. The participants were evaluated in three different gait conditions, according to the starting distance from the obstacle: 1.5m, 3m, and 5m away from the obstacle. Vector coding technique was employed to establish the coupling between head, trunk, and pelvis in the steps immediately before and during obstacle circumvention. Three-way ANOVA's (group, distance, and step) were calculated with the level of significance at p<0.05. For all couplings of coordination, there were no effects of distance. However, significant main effects of group and steps (p<0.05) were found for all couplings with different patterns of coordination: head/pelvis (group: in-phase and anti-phase variables; steps: anti-phase variable), head/trunk (group: trunk variable; steps: in-phase and anti-phase variables) and trunk/pelvis (group: anti-phase; steps: trunk and pelvis). Finally, only head/trunk coupling showed an interaction between group*steps. Individuals with PD showed 7.95% lower head movement (p<0.024) and 14.85% greater trunk movement than CG (p<0.002). Also, individuals with PD performed 17.56% greater head movement in the step before the circumvention compared to the step during circumvention (p<0.044). The starting distance from the obstacle did not influence the pattern of axial intersegmental coordination in both groups. However, how these segments interact in the preparation and during the obstacle circumvention are opposite in individuals with PD. While on the previous step to obstacle circumvention, the head movement was greater than the trunk, during the obstacle circumvention step, individuals with PD rotated the trunk more.

The Role of Cognition When Executing an Online, Visually Evoked Adjustment to an Obstacle Circumvention Strategy

We know that performing simultaneous cognitive tasks during locomotion results in reduced performance on either or both tasks, however the role of the cognitive system in the execution of last-minute changes to ongoing adaptive locomotor tasks is not fully understood. Nineteen participants were initially cued to circumvent to left, right, or step over an obstacle while an auditory cognitive task was simultaneously presented. In half of the trials, no change in avoidance strategy was required; in the remaining trials, participants were visually cued two steps in advance to execute a new circumvention strategy. Participants decreased gait velocity and increased cognitive task response times when executing changes in strategy, highlighting the important role the cognitive system plays in these complex tasks.

Joint-level force sensing for indirect hybrid force/position control of continuum robots with friction

Continuum robots offer the dexterity and obstacle circumvention capabilities necessary to enable surgery in deep surgical sites. They also can enable joint-level ex situ force sensing (JEFS), which provides an estimate of end-effector wrenches given joint-level forces. Prior works on JEFS relied on a restrictive embodiment with minimal actuation line friction and captured model and frictional actuation transmission uncertainties using a configuration space formulation. In this work, we overcome these limitations. First, frictional losses are canceled using a feed-forward term based on support vector regression in joint space. Then, regression maps and their interpolation are used to account for actuation hysteresis. The residual joint-force error is then further minimized using a least-squares model parameter update. An indirect hybrid force/position controller using JEFS is presented with evaluation carried out on a realistic pre-clinically deployable insertable robotic effectors platform (IREP) for single-port access surgery. Automated mock force-controlled ablation, exploration, and knot tightening are evaluated. A user study involving the daVinci Research Kit surgeon console and the IREP as a surgical slave was carried out to compare the performance of users with and without force feedback based on JEFS for force-controlled ablation and knot tightening. Results in automated experiments and a user study of telemanipulated experiments suggest that intrinsic force-sensing can achieve levels of force uncertainty and force regulation errors of the order of 0.2 N. Using JEFS and automated task execution, repeatability, and force regulation accuracy is shown to be comparable to using a commercial force sensor for human-in-the-loop feedback.

Reading text messages at different stages of pedestrian circumvention affects strategies for collision avoidance in young and older adults

BackgroundReading text messages is associated with accidents while walking in community places. Research questionTo what extent does reading text messages at different stages of obstacle circumvention affect avoidance strategies while walking in young vs. older adults? MethodsSixteen healthy young and 14 older adults were assessed while walking and viewing a virtual environment (VE) simulating a subway station with three virtual pedestrians positioned 7.5 m away from the participant in the centre (0°), left and right (±40°). As participants advanced 0.5 m towards a target in the far space, a virtual pedestrian randomly approached them. Text messages were delivered at onset of pedestrian movement (0.5 m; early message) or during obstacle circumvention (2.5 m; late message). A Vicon motion capture system captured trajectory displacement while walking. ResultsIn both age groups, accuracy of message report (AMR) was reduced for early compared to late messages (p < 0.001), although older adults showed larger deterioration (p < 0.001) compared to younger participants. Locomotor outcomes (obstacle clearance, onset time of avoidance and walking speed) showed no differences between young and older participants (p > 0.05). Early messages led to slower walking speed (p < 0.001) and more frequent collisions compared to late messages and the no-message condition. Late messages yielded faster walking speed (p < 0.001) and onset time of avoidance (p < 0.02) compared to the other conditions. SignificanceResults indicate that the stage of an avoidance strategy at which text messages are received impacts on pedestrian circumvention, with early messages posing a greater challenge to collision avoidance. In older adults, the reduced AMR suggests larger dual-task interference and prioritization of the walking task. The lack of further walking speed reduction in older vs. young adults may put them at greater risk of collisions in crowded, unpredictable community environments.

Gaze behavior of healthy young individuals navigating in a community environment

Introduction Independent community walking relies heavily on the sense of vision and involves locomotor adaptations (i.e. changes in speed and direction) that are essential to avoid hazards in the environment (e.g. obstacles). In this project, we are examining gaze behavior and body kinematics as healthy individuals ambulate and avoid other pedestrians in a living lab representing a community environment. To characterize gaze behavior and kinematic strategies during obstacle circumvention while walking in a community environment. Material and methods Twelve healthy young individuals (18–29 yrs) were assessed while walking towards a target with different exposures to static and moving obstacles in Alexis Nihon Mall in Montreal. Kinematics and temporal distance factors were assessed with wearable sensors (APDM) while gaze behavior was recorded with an eye-tracker (Tobii Pro 2). Results Preliminary data analysis (n = 3) indicate that looming vs. receding pedestrians were looked at a closer distance and less frequently, for shorter duration but they yield higher relative gaze fixation duration. Also, right vs. left pedestrians were looked at a further distance. Conclusion Results suggest that looming pedestrians, while present for shorter duration, impose a greater risk of collision. Results further suggest a possible lateralization of attention and maintenance of personal space during collision avoidance. Collectively, present findings will help better understand how visual information is used for obstacle negotiation in a community environment and will serve as a basis for comparison to understand community walking challenges experienced by older adults and individuals with a physical disability.

Intersegmental body coordination during obstacle avoidance in a virtual environment

Introduction Postural coordination is essential for implementing efficient obstacle circumvention strategies during locomotion. While virtual environments (VEs) are increasingly used to replicate real-life conditions and safely assess or train patients on complex locomotor tasks, the extent to which coordination strategies in VEs differ from that observed in the physical environment (PE) remains to be elucidated. Material and methods The objective was to estimate the extent to which coordination strategies in the VE differ from the PE. Healthy young participants (n = 10) were assessed while walking towards a target and avoiding pedestrians approaching from different directions (left, centre, right) in a VE vs. PE. The VE, identical in size and appearance to the PE, was viewed using a HTC VIVE head-mounted display (HMD). Centre of mass trajectory (CoMt), as well as head, thorax and pelvis yaw, were measured using a Vicon system. Results In both environments, participants reoriented their body segments towards their heading direction during obstacle circumvention. In the PE, the reorientation sequence started with the head (2.94 ± 0.04 m from obstacle), followed by the trunk (2.74 ± 0.03 m), pelvis (2.71 ± 0.04 m) and CoMt (2.64 ± 0.04). In the VE, reorientation started with the pelvis (2.97 ± 0.03 m) and trunk (2.95 ± 0.03 m), followed by the head (2.79 ± 0.04 m) and CoMt (2.77 ± 0.04 m). Smaller maximum head reorientation (Δ = 1.72 ± 0.67; P Conclusion Head reorientation was smaller and delayed in the VE, which could be due to the characteristics of HMD and a need for longer visual fixation on the obstacle/target. These differences should be considered when using VR in locomotor rehabilitation.

Parkinson’s patients delay fixations when circumventing an obstacle and performing a dual cognitive task

BackgroundPeople with Parkinson’s disease (PD) do not differ from neurologically healthy individuals in obstacle circumvention during walking, therefore they are able to use visual feedback adequately to control motor behavior in this task. However, individuals are often distracted by the secondary task when circumventing an obstacle. An increased cognitive load can require prolonged gaze fixation time on a location of interest to compensate for longer information processing duration. Research questionTo investigate the effects of cognitive dual tasking (DT) on gaze behavior during waking with obstacle circumvention in people with PD and control group, and to determine the impact of gaze behavior on motor strategy. MethodsFifteen individuals with PD (PD-group) and 15 neurologically healthy individuals walked at a self-selected speed over a walkway and circumvented an obstacle centered in the walkway. The experimental conditions (5 trials each one) included obstacle circumvention without DT (OC) and obstacle circumvention with DT (OCDT). In the cognitive task, the participant mentally counted the number of times a target number appeared in an audio recording. We analyzed gaze behavior (i.e. number of gaze fixations and duration on the ground and obstacle), standard gait measures and DT cost. Two-way ANOVAs were completed for gait parameters and moment of fixation. ResultsThere was no significant difference in DT cost between groups and no obstacle contacts. The participants performed a longer mean duration of fixations on the ground during OCDT compared to OC. Group x condition interactions indicated that the PD-group delayed the obstacle fixation relative to the NHI for OCDT (p < 0.001) and presented greater medial-lateral body clearance (p < 0.001) and longer double support time (p < 0.001) during OCDT compared to OC. SignificanceThe results of this study suggest that deficits in locomotion during DT in PD-group may be caused, at least in part, by a reduced ability to fixate gaze at appropriate times during walking.

Locomotor circumvention strategies in response to static pedestrians in a virtual and physical environment

BackgroundCircumvention of pedestrians is an essential requirement of community ambulation and can be challenging to reproduce in laboratory or clinical settings. Virtual reality (VR) is a powerful tool that allows investigations, assessments or training of such tasks under ecological but controlled conditions. The extent to which current VR technologies can elicit responses similar to those observed in the physical world, however, remains to be determined. Research questions(1) To what extent does the circumvention of static pedestrians in VR differ from that observed in the physical environment (PE)? and; (2) To what extent does the inter-trial variability of obstacle circumvention outcomes differ in VR vs. the PE? MethodsHealthy young participants (n = 13) were assessed while walking and avoiding a collision with an interferer that stood either at 3.0 and 3.5 m from the participant's starting position (experimental trials) or that exited to the side (catch trials). The task was performed in the PE and VE, in a random order. A female collaborator acted as interferer in the PE and her kinematics was used to create the avatar used in the VE. ResultsCompared to the PE, the circumvention of a static pedestrian in VR was characterized by larger obstacle clearances and slower walking speeds. Characteristics of circumvention strategy such as the preferred side of circumvention, response to obstacle position and pattern of speed adaptation were similar between VR and the PE. Inter-trial variability for the different outcomes were also similar between the two environments. SignificanceDifferences in obstacle clearance and speed indicate the use of “safer” circumvention strategies in VR. However, the patterns of locomotor adaptation that were largely similar between the two environments which suggests that VR is a valuable tool to study, assess and possibly train complex locomotor tasks such as obstacle avoidance.

Directionally biased sidestepping of Kip3/kinesin-8 is regulated by ATP waiting time and motor–microtubule interaction strength

Kinesin-8 motors, which move in a highly processive manner toward microtubule plus ends where they act as depolymerases, are essential regulators of microtubule dynamics in cells. To understand their navigation strategy on the microtubule lattice, we studied the 3D motion of single yeast kinesin-8 motors, Kip3, on freely suspended microtubules in vitro. We observed short-pitch, left-handed helical trajectories indicating that kinesin-8 motors frequently switch protofilaments in a directionally biased manner. Intriguingly, sidestepping was not directly coupled to forward stepping but rather depended on the average dwell time per forward step under limiting ATP concentrations. Based on our experimental findings and numerical simulations we propose that effective sidestepping toward the left is regulated by a bifurcation in the Kip3 step cycle, involving a transition from a two-head-bound to a one-head-bound conformation in the ATP-waiting state. Results from a kinesin-1 mutant with extended neck linker hint toward a generic sidestepping mechanism for processive kinesins, facilitating the circumvention of intracellular obstacles on the microtubule surface.