Collision avoidance behaviours while young adults avoid a virtual pedestrian approaching on a 45° angle under attentionally demanding conditions.

Individuals rely on visual information to determine when to adapt their behaviours (i.e., by changing path and/or speed) to avoid an approaching object or person. After initiating an avoidance behaviour, individuals may control the space (i.e., minimum clearance distance) between themselves and another person or object. The current study aimed to determine the action strategies of young adults while avoiding a virtual pedestrian approaching along a 45° angle in an attentionally demanding task. Twenty-one young adults (22.9 ± 1.9 yrs., 11 males) were immersed in a virtual environment and were instructed to walk along a 7.5 m path towards a goal located along the midline. Two virtual pedestrians (VP) positioned 2.83 m to the left and right of the midline approached participants on a 45° angle. To manipulate the point at which the participants and the VP would intersect during different trials, the VP approached at one of three speeds: 0.8×, 1.0×, or 1.2× each participants' average walking speed. Participants were instructed to walk to a goal without colliding with the VP while performing the attention task; reporting whether a shape changed above the VPs' heads. Results revealed that young adults did not modulate their timing of avoidance to the approach characteristics of the VP, as they consistently avoided the collision 1.67 s after the VP began moving. However, young adults seem to control how they avoid an oncoming collision by maintaining a consistent safety margin after an avoidance behaviour was initiated.

A treadmill running research protocol to assess dynamic visual acuity and balance for athletes with and without recent concussion history.

Athletes interpret dynamic visual scenes quickly and accurately during physical exertion. It is important to understand how increased exertion may impact vision and cognition following sport-related concussion (SRC).Purpose To examine the effect of a treadmill running research protocol on the assessment of dynamic visual acuity (DVA) and balance for athletes with and without recent history of SRC.Methods Varsity athletes following recent SRC (CONC=12) were compared to athletes without SRC (ATHLETE=19). The DVA task presented a Tumbling 'E' target in four possible orientations during random walk (RW) or horizontal (H) motion at a speed of 30°/s. Participants performed DVA trials standing on a force plate (1000Hz) at four time points: 1) pre-exercise (PRE-EX), 2) immediately (POST1), 3) 10-minutes (POST10), and 4) 20-minutes post- exercise (POST20). Performance was calculated as a change in DVA score from PRE-EX and median response time (RT, ms). Balance control was analyzed using the root mean square of centre of pressure displacement (dCOP).Results Both groups maintained DVA scores for both motion types and exhibited immediate exercise-induced benefits on RT. Both groups had similar change in balance control strategy following treadmill exercise.Conclusion Both groups elicited similar exercise-induced benefits on DVA following exercise. A repeated measures assessment following vigorous exercise may provide meaningful insights about visual and neurocognitive functions for athletes returning to sport following concussion.

Avoidance behaviours while circumventing to the left or right of someone with different shoulder widths and facing directions: How do side, width, or orientation matter?

BACKGROUND: Collision avoidance during locomotion is influenced by a variety of situational factors. When circumventing around an inanimate object, the amount of clearance is dependent on the side of avoidance. When avoiding other pedestrians, individuals most often choose to walk behind a moving pedestrian, and avoid people differently depending on their body size. However, side of avoidance has not been evaluated with human obstacles, nor facing direction of a stationary pedestrian, nor the size of a single pedestrian. Therefore, the aim of this study is to evaluate these knowledge gaps concurrently. RESEARCH QUESTION: How do people avoid a collision to the left-side or right-side of a single stationary pedestrian (interferer) of varying shoulder width and orientation? METHODS: Participants (n = 11) walked along a 10 m pathway towards a goal, while a stationary interferer stood 6.5 m from the start. The interferer faced one of three directions relative to the participant (orientation); forward, leftward, or rightward, with either their normal shoulder width or enlarged width created by wearing football shoulder pads. Participants were explicitly instructed as to which side of the interferer to avoid (forced-left vs forced-right). Each participant completed 32 randomized avoidance trials. Centre of Mass separation at the time of crossing was used to examine individual's avoidance behaviours. RESULTS: Results revealed no effect of interferer width, but a significant side of avoidance effect, where the centre of mass separation between the participant and interferer at the time of crossing was smallest when participants avoided to their left. SIGNIFICANCE: Findings suggest that changing the facing direction or artificially increasing the shoulder width of a stationary interferer will not affect one's avoidance behaviours. However, an asymmetry in side of avoidance is maintained similar to that observed in obstacle avoidance behaviours.

Aperture Crossing in Virtual Reality: Physical Fatigue Delays Response Time.

Visual perception and cognitive (i.e., decision-making) abilities facilitate successful avoidance of obstacles in a person's environment. However, detrimental changes to cognition can occur after physical fatigue is induced by strenuous exercise. The purpose of the current study was to determine if obstacle avoidance behaviors reflect similar negative effects following physically fatiguing exercise. A virtual reality (VR) closing-gap aperture crossing task was completed by 13 recreationally active individuals to assess the effects of physical fatigue on passability judgements and response time. Participants approached closing apertures that moved at one of seven speeds while deciding to either pass through the closing aperture or stop. Participants completed four blocks of trials over a 7-day period (i.e., pre- and post-tests on the fatiguing day and control day). No significant differences for passability judgements were found across each of the blocks, but there was a significant reduction in response time on the post-test exercise day. Thus, physical fatigue increased the time required to make, and follow through on, a decision. The current findings suggest that processes requiring more cortical areas and processing (i.e., response time) may be more detrimentally affected by physically fatiguing exercise compared to dichotomous visuomotor tasks (i.e., passability judgements).

Collision avoidance behaviors of recently concussed female rugby players with an approaching person.

BACKGROUND: Successful collision avoidance requires individuals to use readily available perceptual information to make decisions and act within their action capabilities. Female varsity rugby players use time-to-collision information to get closer to an obstacle before deviating; however, following a sport-related concussion (SRC), individuals may not be able to use the same strategies due to poorer action boundary perception. The current study examined the effects of a SRC on collision avoidance with an approaching person. METHODS: Non-concussed female varsity rugby athletes (ATH, n = 10) and recently concussed but asymptomatic teammates (CONC, n = 3) were instructed to walk at a comfortable pace and avoid colliding with an approaching confederate. Time-to-collision (TTC), rate of medial-lateral (ML) avoidance, and ML spatial requirement were calculated and analyzed using mixed repeated measures ANOVAs. FINDINGS: There were no physical characteristic differences between groups (p < 0.05) and no collisions occurred on any of the trials. However, CONC displayed larger TTC than ATH (p = 0.03), indicative of a more cautious avoidance strategy. INTERPRETATION: While rugby players are trained to avoid opponents, a more cautious strategy following a SRC may reflect visuomotor detraining and changes in embodiment. This suggests that despite being asymptomatic, there is a reduced sense of agency during dynamic perception-action tasks and persistent alterations between pre-concussion and post-concussion self.

Collision avoidance behaviours between older adult and young adult walkers.

BACKGROUND: Collision avoidance between two walkers requires a mutual adaptation based on visual information in order to be successful. Age-related changes to visuomotor processing, kinesthetic input, and intersegmental dynamics increases the risk of collision and falls in older adults. However, few studies examine behavioural strategies in older adults during collision avoidance tasks with another pedestrian. RESEARCH QUESTION: Is there a difference between older adults' and young adults' collision avoidance behaviours with another pedestrian? METHODS: Seventeen older adults (x¯ = 68 ± 3 years) and seventeen young adults (x¯ = 23 ± 2 years) walked at a comfortable walking speed along a 12.6 m pathway while avoiding another walker. Trials were randomized equally to include 20 interactions with the same age group and 21 interactions with the opposite age group. Minimum predicted distance (mpd) was used to characterize collision avoidance behaviours between older adults and young adults. RESULTS: Older adults had riskier avoidance behaviours, passing closer to the other pedestrian (0.79 m ± 0.18 m) compared to when two young adults were on a collision course (0.93 m ± 0.17 m) (χ²(3) = 35.94, p < .0001). Whenever an older adult was on a collision course with a young adult, the young adult contributed more to the avoidance regardless of passing order. SIGNIFICANCE: The results from the current study highlight age-related effects during a collision avoidance task in older adults resulting in risky behaviour and a potential collision. Future studies should further investigate age-related visuomotor deficits during collision avoidance tasks in cluttered environments using virtual reality in order to tease out factors that contribute most to avoidance behaviours in older adults.

The effects of different environments on older adults' ability to successfully cross a closing gap in virtual reality.

BACKGROUND: To navigate through dynamically changing environments and to avoid collisions with stationary and moving obstacles, older adults tend to over rely on their visual system because it is a more reliable source of information. Aging affects both visuomotor integration and visual perception, often resulting in the inability to produce appropriate adaptive locomotor actions in a timely manner. RESEARCH QUESTION: Does peripheral visual information in the environment affected older adults' ability to complete a gap-crossing task with a set of closing doors at different rates (0.6-1.2 m/s)? METHODS: Fifteen older adults (65-74 years) completed the study inside a virtual environment with three different levels of peripheral visual information: 1) empty; 2) stationary avatars; and 3) moving avatars. Kinematic data was collected using an Optotrak camera system to track the older adults' body movements during the task. RESULTS: The results demonstrated that regardless of the environment or closing door speed, older adults maintained consistent approach speeds. However, older adults collided with the fastest moving doors a significant number of times at the fastest door closing rates for the empty and moving avatar conditions. SIGNIFICANCE: Although it appears that older adults are able to attend on a central task (i.e., passing through closing doors) and maintain constant behaviours regardless of the visual information from peripheral environment, richness of the peripheral environment provides accurate feedback about self-motion affects success rates.

Collision avoidance behaviours when circumventing people of different sizes in various positions and locations.

The current study examined whether young adults' avoidance behaviours differed when circumventing a larger versus smaller interferer. It was expected that avoidance behaviours (repulsion) would be affected by the interferer's size (i.e., greater repulsion for larger body size). Participants (n = 20) walked along an 8 m pathway towards a goal while avoiding either a larger or smaller sized male interferer who stood stationary facing forward, backward, left, or right and were located 2, 4, or 6 m from the participants' starting position. Results revealed that there was an effect of interferer body size (personal-characteristics) and orientation (situational-characteristics) on M-L clearance between the interferer and participant at the time of crossing, suggesting that repulsion magnitudes are scaled to an interferer's closest body surface.

The effects of human following behaviours on decision making during aperture crossing scenarios.

BACKGROUND: Everyday locomotion often requires that we navigate crowded and cluttered environments. Individuals navigating through nonconfined space will require a deviation from the straight path in order to avoid apertures smaller than 1.4 times their shoulder width. When in a crowd, humans will follow the behaviours of those directly in front of them, making changes to their walking speed and direction heading based on the changes made by the people they are following. RESEARCH QUESTION: The current study aimed to discover whether the decisions made by young adults regarding the passability of an aperture would be influenced by the presence of a leader completing the same nonconfined aperture crossing task. METHODS: Participants (N = 24) walked in a virtual reality environment along a 6.5 m pathway towards a goal while avoiding two virtual poles which created an aperture (0.8-1.8 times the participants' shoulder widths). For some trials, a sex-matched avatar (shoulder width of 0.8, 1.0, or 1.2 times the participants' shoulder widths) completed the aperture crossing task, using its own body-scaled information, ahead of the participant. RESULTS: Participants walked through apertures smaller than 1.4 times their shoulder width (i.e. critical point) regardless of avatars' independent behaviours. Participants began to deviate 3.69 m from the aperture on all trials that required a deviation and approached their goal at a slower speed when the avatar was present. SIGNIFICANCE: This study demonstrates that during a nonconfined aperture crossing task, individuals are not influenced by human following behaviours and will continue to make decisions based on their own body-scaled information.

Are avatars treated like human obstacles during aperture crossing in virtual environments?

RESEARCH OBJECTIVE: The current study set out to determine whether individuals walking in a virtual reality environment pass through apertures made of two avatars differently than apertures created by two pole obstacles, as previously observed between pole and human obstacles in real-world environments. METHODS: Eleven healthy young adults wore a head-mounted virtual reality display, walked along a 10 m path and passed through a virtual aperture located 5 m from the starting location. Participants were instructed to avoid colliding with the obstacles when passing through the aperture. The experiment was conducted in a block design, where the aperture was either created by two pole obstacles or by two avatars. In both conditions, the width of the aperture ranged between 1.0-1.8x each participant's shoulder width. RESULTS: Regardless of whether the aperture was created by the virtual poles or the avatars, participants rotated their shoulders for all aperture sizes and results found no significant differences in shoulder rotation angle, onset of rotation, walking speed or velocity at time of crossing between the two types of obstacles. Therefore, it appears that the differences in avoidance behaviours observed in real-world settings between people and pole obstacles is not translated to a virtual reality environment. SIGNIFICANCE: It is possible that during experiments in which the avatars do not move, they do not possess human-like qualities suggested to be responsible for the increased caution used when walking through real human obstacles and instead, are treated as any ordinary obstacle.

Balance control in youth hockey players with and without a history of concussions during a lower limb reaching task.

BACKGROUND: Sport-related concussion (SRC) is a functional injury that affects several clinical domains, including balance and cognition. The purpose of this study was, 1) to determine whether a lower limb visuomotor task could identify balance control differences between youth athletes with and without previous SRC; and 2) if balance is affected by training over time. METHODS: Youth hockey players (n = 34) who reported previous SRC (CONCUSSED; n = 12; mean age = 14.4 yrs., SD = 1.6, mean time from injury = 1.9 yrs., median = 1.7 yrs. [0.6-4.6]) and no history of SRC (CONTROL; n = 22; mean age = 14.7, SD = 1.5) were tested twice over 70 days. Participants stood in single support on a Nintendo Wii Balance board sampled at 100 Hz and performed Go/No-Go tasks with each foot. Five FitLight Trainer™ (Aurora, ON) lights were arranged on the floor at 60°, 30°, and 0° and illuminated in random GREEN (Go) or RED (No-Go). Balance was assessed using root mean square displacement and velocity of CoP in anterior-posterior and medial-lateral directions. FINDINGS: CONCUSSED had significantly lower velocity of CoP in the anterior-posterior (F(1, 32) = 13.81, p < .001) and medial-lateral (F(1, 32) = 13.80, p < .001) directions than CONTROL, with no learning effects over time (anterior-posterior: F(1, 32) = 0.30, p = .137: F(1, 32) = 0.91, p = .346; medial-lateral: F(1, 32) = 0.91, p = .346). These findings suggest that CONCUSSED consistently performed the task more conservatively. INTERPRETATION: A lower limb Go/No-Go task may objectively identify differences between youth athletes with and without previous SRC. These visuomotor and balance control deficits may persist beyond clinical recovery.

The effect of galvanic vestibular stimulation on path trajectory during a path integration task.

The purpose of this study was to determine the effects of galvanic vestibular stimulation (GVS) on path trajectory and body rotation during a triangle completion task. Participants ( N = 17, female, 18-30 years) completed the triangle completion task in virtual reality using two different size triangles. GVS was delivered at three times each participant's threshold in either the left or right direction prior to the final leg of the triangle and continued until the participant reached their final position. Whole body kinematics were collected using an NDI Optotrak motion tracking system. Results revealed a significant main effect of GVS on arrival error such that no GVS (NGVS) had significantly smaller arrival errors than when GVS was administered. There was also a significant main effect of GVS on angular error such that NGVS had significantly smaller error than GVSaway and GVStowards. There was no significant difference between GVS trials in path variability during the final leg on route to the final position. These results demonstrate that vestibular perturbation reduced the accuracy of the triangle completion task, affecting path trajectory and body position during a path integration task in the absence of visual cues.

The effects of sport specific training of rugby players on avoidance behaviours during a head-on collision course with an approaching person.

Individuals use visual information to plan and adapt movements to dynamically changing environments. This information is used to accurately determine when and where they may come in contact with an object. More specifically, individuals may determine the time prior to contacting an object, known as time-to-contact (TTC). Sport provides a scenario where athletes compete in dynamically changing environments and must interact with opposing players. The effects of sport-specific training on obstacle avoidance is highly controversial and research suggests the quantifiable differences in behaviours compared to non-athletes is highly context specific. The current study aimed to examine if sport-specific training has an impact on the avoidance behaviours of rugby players during a head-on collision course with an approaching person. Female rugby players (N = 10, x- = 20 ±â€¯0.94 years) and non-athletes (N = 10, x- = 21.9 ±â€¯1.6 years) were instructed to walk along a 10 m path towards a goal located along the midline. A female confederate initially positioned along the midline 180° from the participant walked towards the participant to one of four predetermined final positions: 1) along the midline in the participants' starting position; 2) stopped along the midline 2.5 m from her starting position; 3) to the left of the participants' starting position; and 4) to the right of the participants' starting position. Results revealed when the path of the confederate was uncertain, individuals used a consistent TTC to determine when to change their path. The rugby players in the current study were found to avoid significantly later (i.e. smaller TTC) than non-athletes. However, following a change in path, sport-specific training did not impact the avoidance behaviours of the groups, but rather the environment was the regulating factor. When the path of the confederate was uncertain, individuals did not use a single avoidance strategy, instead considered the fit between their individual characteristics (i.e., action capabilities) and components of the environment (i.e. path of the confederate and task constraints). Athletes who are specifically trained to pass through spaces and avoid obstacles (i.e., rugby backs) may consider their action capabilities in conjunction with their visual information to determine time of avoidance.

Avoidance behaviours of young adults during a head-on collision course with an approaching person.

Individuals use visual information to guide their avoidance behaviours. More specifically, individuals may directly perceive the time prior to colliding with an approaching obstacle (i.e., time to contact, TTC) to determine when to avoid. In addition, individuals use body-scaled information to control their movements. These avoidance behaviours differ when avoiding a human obstacle compared to an inanimate object. As such, the purpose of this experiment was to examine the avoidance behaviours of individuals during a head-on collision course with an approaching person. Young adults (N = 20, [Formula: see text] = 22.25 ± 1.5 years, 10 males) were instructed to walk along a 10 m path towards a goal located along the midline. A female confederate positioned along the midline walked towards the participants to one of the four predetermined final positions: (1) along the midline in the participants' starting position; (2) stopped along the midline 2.5 m from her starting position; (3) to the left of the participants' starting position; and (4) to the right of the participants' starting position. Results revealed when the path of the confederate was certain, individuals used a greater TTC to determine when to change their path in comparison with when the path of the confederate was uncertain. Males were found to avoid significantly earlier (i.e., larger TTC) than females. However, following a change in path, sex did not impact the avoidance behaviours of the groups, but rather, the environment was the regulating factor.

The Effects of Obstacle Type and Locomotion Form on Path Selection in Rugby Players.

The current study investigated whether path selection of athletes specifically trained to fit through gaps is affected by the location of human obstacle and the form of locomotion. Female rugby players were instructed to walk, walk with the ball, or run with the ball along a path toward a goal while avoiding three obstacles (three vertical poles or two vertical poles and a confederate) placed halfway along the path, creating two equal apertures of 80 cm. Regardless of the form of locomotion, rugby players chose paths furthest from the confederate, suggesting that confederate location affects path selection. Furthermore, medial-lateral spatial requirements were more variable when participants were walking without the ball than while moving with the ball. Avoidance behaviors, but not path selection, appear to be impacted and minimized during sport-specific movements.

Action strategies for walking through multiple, misaligned apertures.

When avoiding obstacles, path selection is thought to be determined by the attraction of the end-goal. However for aperture crossing, it is unclear whether the attraction point originates in the center of the aperture or at the end-goal, as previous experiments align the aperture with the end-goal. The purpose of the current study was to decipher the possible location of the attraction point, by evaluating crossing behaviour for multiple, misaligned apertures. Participants were instructed to walk through three separate apertures while en route to an end-goal. The first and last apertures were fixed such that they were both either 0.9× or 1.7× shoulder width (SW) while the second aperture was either 0.9, 1.3 or 1.7× SW and shifted 25, 50 or 75cm off the midline. Findings revealed that the attraction of the end-goal, and not the middle of the aperture, guided crossing behaviour. The spatial margin decreased as the size of the shift increased. Furthermore, the frequency of rotation increased as the aperture was shifted away from midline, regardless of the aperture size. Since rotations would not normally occur for all of these aperture sizes when aligned with the end-goal, these results suggest that rotations were produced in an attempt to keep one's trajectory as close to the midline as possible. Therefore, not only does the attraction of the goal guide path trajectory, but individuals will choose to reduce the spatial margin and rotate the shoulders when walking through misaligned apertures, likely in attempt to maintain the straightest possible path.

The effects of exercise on a choice reaction time task in individuals with post-concussion syndrome.

PURPOSE: To assess cognitive performance differences pre- and post-exercise in individuals without concussion (non-concussed, NC) and individuals with post-concussion syndrome (PCS). METHODS: A total of 30 participants completed a choice reaction time (CRT) task in the form of an iPad application, measuring each individual's decision-making capabilities, while wearing a head-mounted eye tracker system. Participants completed four blocks of testing; the time interval between the first two blocks of trials and the last two blocks of trials was 10 minutes. Between the completion of block 2 and the start of block 3, the participants completed a 15-minute bout of exercise. RESULTS: Individuals with PCS at rest and following exercise displayed greater average reaction time (RT) (p<.01), lower overall accuracy (p<.01) and shorter final fixation durations (p<.05) than NC. Combined influence of learning and exercise resulted in a significant difference (p<.05) in RT from block 1 to block 3 and block 1 to block 4. CONCLUSION: Persistent concussion-based symptoms may be indicative of deficits in higher-level cognitive processing, as indicated by both decreased CRT performance and differences in gaze behaviours between groups. Therefore, individuals with PCS may not elicit appropriate decisions when navigating through an environment, potentially leading to further risk of injury.

The effects of obstacle proximity on aperture crossing behaviours.

Affordance theory and behavioural dynamics have been used as theoretical constructs to explain how individuals interact with the environment in order to avoid obstacles. Features of obstacle distance and multiple obstacle avoidance have been discussed in unique studies, yet the interactions of these environmental features have yet to be explored. The purpose of this study was to asses the effects of obstacle distance, relative to the goal, on aperture crossing strategies. Kinematics and gaze behaviours were assessed in a cohort of female young adults (N = 24, 21.3 ± 1.4 years). Results identified that participants chose to navigate through gaps of 1.3× shoulder width or greater, regardless of obstacle distance. However, safety margin in the anterior-posterior direction was found to increase with increased obstacle distance, suggesting unique environmental affordances for each obstacle distance. Therefore, although decision making on whether to navigate through, or around, the aperture appears to be unaffected by obstacle location, specific environmental features result in unique kinematic behaviours. Such behaviours fit within, and add merit to, the tenets of both affordance theory and behavioural dynamics.

Using a Manipulation Check to Uncover Age-Related Difference in Focus of Attention Instruction During a Balance Task.

BACKGROUND/STUDY CONTEXT: A manipulation check was used to investigate whether there is an age-related difference in the adherence to specific external- and internal-focus instructional constraints. METHODS: Participants stood on a force platform and were to maintain a feedback cursor (representing their center of pressure) along the horizontal direction, within a target on a computer monitor. Trials were conducted with either an external focus of attention (keeping the feedback cursor within the target) or an internal focus of attention (keeping the weight evenly distributed between both legs). RESULTS: The finding showed that younger adults followed the experimental instructions; however, older adults relied on external visual information when they were asked to focus on the body movements. CONCLUSION: Age-related declines may contribute to attention allocation differences. The authors propose that specific manipulation checks be used to ensure proper adherence to instructions when comparing age-related differences in postural control.

Limit cycle oscillations in standing human posture.

Limit cycle oscillations (LCOs) are a hallmark of dynamic instability in time-delayed and nonlinear systems such as climate change models, biological oscillators, and robotics. Here we study the links between the human neuromuscular system and LCOs in standing posture. First, we demonstrate through a simple mathematical model that the observation of LCOs in posture is indicative of excessive neuromuscular time-delay. To test this hypothesis we study LCOs in the postural sway of individuals with multiple sclerosis and concussed athletes representing two different populations with chronically and acutely increased neuromuscular time-delays. Using a wavelet analysis method we demonstrate that 67% of individuals with multiple sclerosis and 44% of individuals with concussion exhibit intermittent LCOs; 8% of MS-controls, 0% of older adults, and 0% of concussion-controls displayed LCOs. Thus, LCOs are not only key to understanding postural instability but also may have important applications for the detection of neuromuscular deficiencies.