Analysis of gait kinematics to determine the effect of manipulating the appearance of stairs to improve safety: a linked series of laboratory-based, repeated measures studies

Background: Falls on stairs are a common and dangerous problem for older people. This series of studies evaluated whether or not selected changes to the appearance of stairs could make them safer for older people to negotiate. Objectives: To determine the effect of (1) a step edge highlighter and its position and (2) an optimised horizontal–vertical (H–V) visual illusion placed on a step riser on gait safety during stair descent and ascent. Design: A series of studies using a repeated measures, laboratory-based design, investigating gait control and safety in independently mobile older people. Setting: The University of Bradford Vision and Mobility Laboratory. Participants: Fit and healthy older people aged 60 years of age or more, independently mobile, reasonably active and with normal healthy eyes and corrected vision. Interventions: A step edge highlighter in a variety of offsets from the stair edge and an optimised H–V visual illusion placed on the stair riser. The H–V illusion was provided on a staircase by horizontal step edge highlighters on the tread edges and vertical stripes on the step risers. Main outcome measures: Gait parameters that are important for safe stepping in ascent and descent, measured using three-dimensional lower limb segmental kinematic data

Audiovisual integration increases the intentional step synchronization of side-by-side walkers

When people walk side-by-side, they often synchronize their steps. To achieve this, individuals might cross-modally match audiovisual signals from the movements of the partner and kinesthetic, cutaneous, visual and auditory signals from their own movements. Because signals from different sensory systems are processed with noise and asynchronously, the challenge of the CNS is to derive the best estimate based on this conflicting information. This is currently thought to be done by a mechanism operating as a Maximum Likelihood Estimator (MLE). The present work investigated whether audiovisual signals from the partner are integrated according to MLE in order to synchronize steps during walking. Three experiments were conducted in which the sensory cues from a walking partner were virtually simulated. In Experiment 1 seven participants were instructed to synchronize with human-sized Point Light Walkers and/or footstep sounds. Results revealed highest synchronization performance with auditory and audiovisual cues. This was quantified by the time to achieve synchronization and by synchronization variability. However, this auditory dominance effect might have been due to artifacts of the setup. Therefore, in Experiment 2 human-sized virtual mannequins were implemented. Also, audiovisual stimuli were rendered in real-time and thus were synchronous and co-localized. All four participants synchronized best with audiovisual cues. For three of the four participants results point toward their optimal integration consistent with the MLE model. Experiment 3 yielded performance decrements for all three participants when the cues were incongruent. Overall, these findings suggest that individuals might optimally integrate audiovisual cues to synchronize steps during side-by-side walking.info:eu-repo/semantics/publishedVersio

Are age-related changes in perceptual-motor regulation related to an increased falls risk?

Introduction Decades of research have shown that approximately one in three older adults, aged 65 years or older, falls at least once each year (Campbell et al., 1990; World Health Organization, 2007). This is a problem in our ageing society; as the number of people in this aged cohort continues to increase, leading to an expected increase of falls and falls related medical costs in the coming years (Hendrie, Hall, Arena, & Legge, 2004). The consequences of falling are not only severe in terms of medical costs, for older adults a fall means injuries, decreases in quality of life and could even lead to death (Burns, Stevens, & Lee, 2016). The current thesis adopts an ecological approach to investigate opportunities for falls prevention. According to an ecological approach, guidance of action is mediated by the perception of ‘opportunities for action’ or ‘affordances’ (Gibson, 1979). These affordances are always action scaled; a person perceives possibilities for action in relation to his or her own action system. For instance, a curb might afford ‘stepping onto’ for me, as I have sufficient leg length and strength to perform a step up, however, it will afford ‘climbing onto’ for a toddler who’s legs might not yet have the length to afford stepping onto the curb. Perception of affordances is therefore influenced by how well a person knows his or her own capabilities or in other words how well one ‘calibrates’ perception and action. To achieve this calibration, one needs to experience of ‘explore’ one’s action system, or, as Gibson (1979) put it: "…we must perceive in order to move, but we must also move in order to perceive" (p. 213). This cyclic nature of perception forms the basis for the perception and action cycle and perceptual-motor coupling. The perception and action cycle can help to understand successful movement and therefore potentially to explain movement errors (such as the ones leading to falls) as well. If one component of the perception and action cycle is unsuccessful it could affect success in movement. For instance, if a person would not calibrate properly, making one insecure about one’s own action capabilities, it might lead to insecurities in moving around. From this it follows that for successful performance, it is important to successfully couple perception and action. Aims, Methods and Results per Study The current study incorporates four inter-related studies with differing methods. The first study (described in Chapter 2) is a systematic review, which sought to investigate the perceptual-motor calibration component of the perception and action cycle. The aim of this study was to assess in what conditions calibration occurs most efficiently, with a sub-aim to assess what is known about age-related changes in calibration. Seven databases were screened to identify literature that combined topics related to ‘perception’, ‘action’ and ‘calibration’ or ‘scaling’. Twenty-three papers satisfied the inclusion criteria. Results of the first study showed that calibration occurs rapidly if the movements performed to explore the perceptual and action coupling provide relevant information for perception. For instance, when standing height is raised by placing a participant on 10-cm high blocks, calibration occurred rapidly when participants were allowed to walk with the block (allowing much exploration), but not when only allowed standing stationary with no body movement (Mark, Balliett, Craver, Douglas, & Fox, 1990). Furthermore, this study identified a general limitation in the research on calibration; no studies have been identified that have studied calibration to changed action capabilities in an older cohort. The second, third and fourth study in this thesis (described in Chapter 4, Chapter 5 and Chapter 6) all use the same ‘curb-approach task’ to study the regulation of gait towards a target. For each trial in the curb approach task, participants were positioned at the far end of an 8m long GAITRite pressure sensitive walkway (GAITRite®, CIR Systems, Inc., Franklyn, NJ, USA). At a ‘go’ signal, participants started walking the length of the walkway (placing one footfall on a target that was randomly placed in the first 3 meters of the walk to prevent participants from performing identical walks in each trial), to the end of the walkway where a curb-like platform (L: 2m, W: 1m, H: 0.15m) was positioned. Participants stepped onto the platform and continued to the far end at which a push-button was positioned that signaled the end of the trial. 33 trials were performed per participant. Outcome measures of the curb-approach task were related to three analyses introduced in previous studies in locomotor pointing (De Rugy, Taga, et al., 2002; Montagne et al., 2000). Firstly, an analysis was introduced that assessed the changes in variability (standard deviation) of the position of foot placements. Secondly, an analysis was introduced that assessed whether the timing of the initiation of adaptations in gait (deviations from a ‘standard’ step) are related to the total amount of adjustments to be made (indicating a perception-action coupling). Finally, an analysis was introduced VII that assessed the strength of perceptual-motor coupling; the degree to which changes in step length depended on the perception of required adjustments. The second study (as described in Chapter 4) aimed to assess whether successful performance in the curb-approach task required similar perceptual-motor regulation compared to the long-jump run up. Sixteen younger adults were included and ask to perform the curb-approach task. Results confirmed the similarities between the curb-approach and the long jump approach. Regulation seemed to be initiated earlier in the curb-approach compared to the long jump, but a similar pattern was observed in decreasing variability of foot placement and an increasingly stronger perceptual-motor coupling as participants got closer to their target in both tasks. The second study concluded that the curb-approach task would provide an effective paradigm to study perceptual-motor regulation in an older cohort (for whom a long jump would be too demanding). The third study (Chapter 5) aimed to assess age-related changes in regulation in the curb approach task. In this study, the data collected from the 16 younger participants (study2) was compared to data collected from a cohort of 105 older adults. Results showed that with older age, participants showed less variability in foot placement during their approach. Furthermore, it was shown that with age, participants were more likely to adopt a strategy that involved shortening rather than lengthening of steps. Age-related changes were most prominent in the measures of strength of perceptual-motor regulation. Similar to the younger participants, older participants showed an increased strength of coupling (or in other words; made stronger adjustments) as they got closer to the curb. However, it was also shown that with age the strength of the coupling over all steps increased, indicating that the older participants made stronger gait adaptations. As the third study identified that age-related changes are most prominent in the measures of perceptual-motor coupling, it was decided to focus the final study (Chapter 6) on the question whether these changes could be related to an increased risk of falls. Ninety-eight participants were included in the analysis for this study, who first performed the curb-approach task and then were entered in a 12 –month follow-up to screen for the occurrence of gait-related falls. Results showed that participants who reported experiencing a gait-related fall showed stronger perceptual-motor coupling (stronger gait adaptations) in stepping onto the curb. Discussion and Conclusion The results of this thesis showed that the curb-approach task provides a novel and valid method to measure perceptual-motor regulation of locomotor pointing in in a low demands setting, suitable for the older cohort. Older adults showed stronger gait adaptations compared to their younger counterparts and adaptations in the step onto the curb were stronger still in on older adults prone to experiencing gait-related falls. These results suggest that, in controlling gait, humans are capable of changing the strength of perceptual-motor coupling in accordance with the difficulty of the task. With age, action capabilities decrease and the curb-approach task becomes harder; our results show that this is met with a strengthening of perceptual-motor coupling. Implications of the current thesis are that in falls risk screenings as well as falls prevention, it is important to consider the entire perception and action cycle. An ecologically-grounded functional approach to healthy aging is advocated which considers a person in relation to his/her behavior and environment (Vaz, Silva, Mancini, Carello, & Kinsella-Shaw, 2017)

Failures in adaptive locomotion in healthy young adults

Young adults fall most frequently when walking, and trips account for 25% of these falls (Heijnen & Rietdyk, 2016). Common approaches to understanding tripping include the examination of behavior when a stationary obstacle is crossed successfully, or to deliberately trip the participant with a covert obstacle. However, these approaches do not establish the underlying cause of failure; examining inadvertent failures does, as this occurs most often in the field (Heijnen & Rietdyk, 2016). In order to identify the behavior that results in obstacle contact, this dissertation examined gait characteristics during inadvertent failures and manipulated the sensory information available to guide the limb trajectory. Manipulating the availability of sensory information is important to determine the information used to successfully guide the limbs, particularly the trail limb. Three experiments were conducted to systematically examine the role of visual and somatosensory information in young adults. I hypothesized that young adults would contact the obstacle due to incorrect foot placement when visual and somatosensory information were not manipulated. I hypothesized that healthy young adults would be able to use an obstacle memory to successfully cross the obstacle when both feedforward visual information and somatosensory information regarding obstacle contact were not available. Finally, I hypothesized that healthy young adults would progressively decrease foot clearance, resulting in values that would result in contact if the obstacle were still in place, when somatosensory information regarding obstacle contact was not available. My work has increased the understanding of several factors related to adaptive locomotion: failures, obstacle memory, and limb independence. First, obstacle contacts occurred most frequently with the trail limb and were mainly due to inadequate foot elevation. Obstacle contacts were caused by a progressive decrease in foot elevation with repeated trials in combination with high variability. Second, humans used an obstacle memory to guide the trail limb over the obstacle, and visual information gathered while walking up to the obstacle was important to establish this obstacle memory. Knowledge of results (i.e. failures) was used to update the obstacle memory. Finally, different behavior between the lead and the trail limb supported the argument that the limbs are controlled independently. Overall, a wide variety in behavior between participants was observed, highlighting the difficulties in developing a universal fall-prevention program. My work has expanded the understanding of adaptive locomotion by establishing the cause of inadvertent failures and the sensory information used to establish an obstacle memory in order to ensure safe travel through a cluttered environment

Keeping Safe : Intra-individual Consistency in Obstacle Avoidance Behaviour Across Grasping and Locomotion Tasks

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Jutta Billino was supported by grants from the German Research Foundation, Collaborative Research Centre SFB/TRR 135: Cardinal Mechanisms of Perception.Peer reviewedPublisher PD

Virtual reality-based assessment and rehabilitation of functional mobility

The advent of virtual reality (VR) as a tool for real-world training dates back to the mid-twentieth century and the early years of driving and flight simulators. These simulation environments, while far below the quality of today’s visual displays, proved to be advantageous to the learner due to the safe training environments the simulations provided. More recently, these training environments have proven beneficial in the transfer of user-learned skills from the simulated environment to the real world [5, 31, 48, 51, 57]. Of course the VR technology of today has come a long way. Contemporary displays boast high-resolution, wide-angle fields of view and increased portability. This has led to the evolution of new VR research and training applications in many different arenas, several of which are covered in other chapters of this book. This is true of clinical assessment and rehabilitation as well, as the field has recognized the potential advantages of incorporating VR technologies into patient training for almost 20 years [7, 10, 18, 45, 78]

When an object appears unexpectedly: object circumvention in adults

Obstacles often appear unexpectedly in our pathway and these require us to make immediate adjustments. Despite how regularly we encounter such situations only few studies have considered how we adjust to unexpected obstacles in the pathway which require us to walk around them. The current study considered how adults adjust to the possibility of an obstacle appearing and then also how foot placement is adjusted to circumvent an obstacle. Fifteen healthy adults walked down an 11m walkway, initially they were told this was a clear pathway and nothing in the environment would change (no gate), they then performed a series of trials in which a gate may (gate close) or may not (gate open) partially obstruct their pathway. We found that medio-lateral trunk velocity and acceleration was significantly increased when there was the possibility of an obstacle but before the obstacle appeared. This demonstrates an adaptive walking strategy which seems to enable healthy young adults to successfully circumvent obstacles. We also categorised foot placement adjustments and found that adults favoured making shorter and wider steps away from the obstacle. We suggest this combination of adjustments allows participants to maintain stability whilst successfully circumventing the obstacle

A methodology for the Lower Limb Robotic Rehabilitation system

The overall goal of this thesis is to develop a new functional lower limb robot-assisted rehabilitation system for people with a paretic lower limb. A unilateral rehabilitation method is investigated, where the robot acts as an assistive device to provide the impaired leg therapeutic training through simulating the kinematics and dynamics of the ankle and lower leg movements. Foot trajectories of healthy subjects and post-stroke patients were recorded by a dedicated optical motion tracking system in a clinical gait measurement laboratory. A prototype 6 degrees of freedom parallel robot was initially built in order to verify capability of achieving singularity-free foot trajectories of healthy subjects in various exercises. This was then followed by building and testing another larger parallel robot to investigate the real-sized foot trajectories of patients. The overall results verify the designed robot’s capability in successfully tracking foot trajectories during different exercises. The thesis finally proposes a system of bilateral rehabilitation based on the concept of self-learning, where a passive parallel mechanism follows and records motion signatures of the patient’s healthy leg, and an active parallel mechanism provides motion for the impaired leg based on the kinematic mapping of the motion produced by the passive mechanism

Associations between gait-related falls and gait adaptations when stepping onto a curb: A prospective falls study

Objectives. Examine gait regulation during the approach to stepping onto a curb for older adults who did or did not report gait-related falls over a 12-month follow-up. Methods. Ninety-eight participants aged 60 years and older were analyzed. Primary outcomes were step length adaptations (lengthening or shortening) during a curb approach and the occurrence of a gait-related fall during a 12-month follow-up. Results. Linear-mixed effects modelling indicated stronger adaptations towards the end of the approach. Participants who reported experiencing a gait-related fall showed a stronger relationship between the adjustment required and adjustment produced; indicating different gait adaptations during the step leading onto the curb. Discussion. The link between prospective gait-related falls and gait-adaptations indicated that older adults with reduced capabilities require stronger adaptations to complete tasks reminiscent of everyday life. This finding may provide insight into the mechanisms of falls in older adults and should inform new falls prevention interventions