Accuracy and Precision of a Novel Photogate System to Measure Toe Clearance on Stairs.

Background: Toe clearance on stairs is typically measured using optoelectronic systems, though these are often constrained to the laboratory, due to their complex setups. Here we measured stair toe clearance through a novel prototype photogate setup and compared this to optoelectronic measurements. Methods: Twelve participants (age 22 ± 3 years) completed 25 stair ascent trials, each on a seven-step staircase. Toe clearance over the fifth step edge was measured using Vicon and the photogates. Twenty-two photogates were created in rows through laser diodes and phototransistors. The height of the lowest photogate broken at step-edge crossing was used to determine photogate toe clearance. A limits of agreement analysis and Pearson's correlation coefficient compared the accuracy, precision and relationship between systems. Results: We found a mean difference of -1.5 mm (accuracy) between the two measurement systems, with upper and lower limits (precision) of 10.7 mm and -13.8 mm, respectively. A strong positive correlation was also found (r = 70, n = 12, p = 0.009) between the systems. Discussion: The results suggest that photogates could be an option for measuring real-world stair toe clearances, where optoelectronic systems are not routinely used. Improvements to the design and measurement factors may help to improve the precision of the photogates.

Using a stair horizontal-vertical illusion to increase foot clearance over an inconsistently taller stair-riser.

INTRODUCTION: Stair falls can be caused by inconsistent stair dimensions. During ascent, inconsistently taller stair risers lead to reduced foot clearances as the inconsistency goes unnoticed. A stair horizontal-vertical illusion increases perceived riser heights and foot clearance and could offset reduced foot clearances over inconsistently taller risers, though this might impact other stair safety measures. METHOD: Twelve participants (age: 22 (3) years) ascended a seven-step staircase under three conditions: i) all steps consistent in riser height (consistent), ii) a 1cm increase in step 5 riser height (inconsistent) and iii) a 1cm increase in step 5 riser height, superimposed with a stair horizontal-vertical illusion (illusion). Vertical foot clearance, foot overhang, and margins of stability were assessed over step 4, 5 and 6. Perceived riser height due to the illusion was determined through a computer perception test. A One-Way Repeated Measures ANOVA compared biomechanical variables between conditions. A One Sample t test compared perceived riser height to the true height. RESULTS: Over the inconsistent step 5, foot clearance reduced by 0.8cm compared to consistent. Illusion increased foot clearance by 1.1cm and decreased foot overhang by 4% compared to inconsistent. On step 4 the illusion led to more anterior instability compared to inconsistent. Illusion and inconsistent led to more mediolateral stability compared to consistent. The illusion increased perceived riser height by 12%. DISCUSSION: Foot clearance reductions over inconsistently taller risers can be offset by a stair horizontal-vertical illusion. Additional benefits included a safer foot overhang and unaffected stability over the inconsistent riser. Changes to step 4 stability might have resulted from leaning forward to look at the step 5 illusion. The stair horizontal-vertical illusion could be a practical solution for inconsistently taller stair risers, where a rebuild is usually the only solution.

The next step in optimising the stair horizontal-vertical illusion: Does a perception-action link exist in older adults?

INTRODUCTION: Tripping on stairs results from insufficient foot to step edge clearance and can often lead to a fall in older adults. A stair horizontal-vertical illusion is suggested to increase the perceived riser height of a step and increase foot clearance when stepping up. However, this perception-action link has not been empirically determined in older adults. Previous findings suggesting a perception-action effect have also been limited to a single step or a three-step staircase. On larger staircases, somatosensory learning of step heights may be greater which could override the illusory effect on the top step. Furthermore, the striped nature of the existing stair horizontal-vertical illusion is associated with visual stress and may not be aesthetically suitable for use on public stairs. These issues need resolving before potential future implementation on public stairs. METHODS: Experiment 1. A series of four computer-based perception tests were conducted in older (N = 14: 70 ± 6 years) and young adults (N = 42: 24 ± 3 years) to test the influence of different illusion designs on stair riser height estimation. Participants compared images of stairs, with horizontal-vertical illusions or arbitrary designs on the bottom step, to a plain stair with different bottom step riser heights and selected the stair they perceived to have the tallest bottom riser. Horizontal-vertical illusions included a previously developed design and versions with modified spatial frequencies and mark space ratios. Perceived riser height differences were assessed between designs and between age groups. Experiment 2. To assess the perception-action link, sixteen older (70 ± 7 years) and fifteen young (24 ± 3 years) adults ascended a seven-step staircase with and without horizontal-vertical illusions tested in experiment 1 placed onto steps one and seven. Foot clearances were measured over each step. To determine whether changes in perception were linked to changes in foot clearance, perceived riser heights for each horizontal-vertical illusion were assessed using the perception test from experiment 1 before and after stair ascent. Additional measures to characterise stair safety included vertical foot clearance, margins of stability, foot overhang, stair speed, and gaze duration, which were assessed over all seven steps. RESULTS: Experiment 1. All horizontal-vertical illusion designs led to significant increases in the perceived riser height in both young and older adults (12-19% increase) with no differences between age groups. Experiment 2. On step 7, each horizontal-vertical illusion led to an increase in vertical foot clearance for young (up to 0.8 cm) and older adults (up to 2.1 cm). On step 1 significant increases in vertical foot clearance were found for a single horizontal-vertical illusion when compared to plain (1.19 cm increase). The horizontal-vertical illusions caused significant increases in the perceived riser height (young; 13% increase, older; 11% increase) with no differences between illusion design, group or before and after stair ascent. No further differences were found for the remaining variables and steps. CONCLUSION: Results indicate a perception-action link between perceived riser height and vertical foot clearance in response to modified versions of the horizontal-vertical illusion in both young and older adults. This was shown with no detriment to additional stair safety measures. Further evaluating these illusions on private/public stairs, especially those with inconsistently taller steps, may be beneficial to help improve stair safety for older adults.

Influence of step-surface visual properties on confidence, anxiety, dynamic stability, and gaze behaviour in young and older adults.

BACKGROUND: Step-surface visual properties are often associated with stair falls. However, evidence for decorating stairs typically concerns the application of step-edge highlighters rather than the entire step-surface. Here we examine the influence of step-surface visual properties on stair descent safety, with a view to generating preliminary evidence for safe stair décor. METHODS: Fourteen young (YA: 23.1 ± 3.7 years), 13 higher (HAOA: 67 ± 3.5) and 14 lower (LAOA: 73.4 ± 5.7) ability older adults descended a seven-step staircase. Older adults were stratified based on physiological/cognitive function. Step-surface décor patterns assessed were: Black and white (Busy); fine grey (Plain); and striped multicolour (Striped); each implemented with/without black edge-highlighters (5.5 cm width) totalling six conditions. Participants descended three times per condition. Confidence was assessed prior to, and anxiety following, the first descent in each condition. 3D kinematics (Vicon) quantified descent speed, margin of stability, and foot clearances with respect to step-edges. Eye tracking (Pupil-labs) recorded gaze. Data from three phases of descent (entry, middle, exit) were analysed. Linear mixed-effects models assessed within-subject effects of décor (×3) and edge highlighters (×2), between-subject effects of age (×3), and interactions between terms (α = p < .05). RESULTS: Décor: Plain décor reduced anxiety in all ages and abilities (p = .032, effect size: gav = 0.3), and increased foot clearances in YA and HAOA in the middle phase (p < .001, gav = 0.53), thus improving safety. In contrast, LAOA exhibited no change in foot clearance with Plain décor. Patterned décor slowed descent (Busy: p < .001, gav = 0.2), increased margins of stability (Busy: p < .001, gav = 0.41; Striped: p < .001, gav = 0.25) and reduced steps looked ahead (Busy: p = .053, gav = 0.25; Striped: p = .039, gav = 0.28) in all ages and abilities. This reflects cautious descent, likely due to more challenging conditions for visually extracting information about the spatial characteristics of the steps useful to guide descent. Edge highlighters: Step-edge highlighters increased confidence (p < .001, gav = 0.53) and reduced anxiety (p < .001, gav = 0.45) in all ages and abilities and for all décor, whilst removing them slowed descent in HAOA (p = .01, gav = 0.26) and LAOA (p = .003, gav = 0.25). Step-edge highlighters also increased foot clearance in YA and HAOA (p = .003, gav = 0.14), whilst LAOA older adults showed no adaptation. No change in foot clearances with décor or step-edge highlighters in LAOA suggests an inability to adapt to step-surface visual properties. CONCLUSION: Patterned step surfaces can lead to more cautious and demanding stair negotiation from the perspective of visually extracting spatial information about the steps. In contrast, plain décor with step edge highlighters improves safety. We therefore suggest plain décor with edge highlighters is preferable for use on stairs.

Constancy of Preparatory Postural Adjustments for Reaching to Virtual Targets across Different Postural Configurations.

Postural and movement components must be coordinated without significant disturbance to balance when reaching from a standing position. Traditional theories propose that muscle activity prior to movement onset create the mechanics to counteract the internal torques generated by the future limb movement, reducing possible instability via centre of mass (CoM) displacement. However, during goal-directed reach movements executed on a fixed base of support (BoS), preparatory postural adjustments (or pPAs) promote movement of the CoM within the BoS. Considering this dichotomy, the current study investigated if pPAs constitute part of a whole-body strategy that is tied to the efficient execution of movement, rather than the constraints of balance. We reasoned that if pPAs were tied primarily to balance control, they would modulate as a function of perceived instability. Alternatively, if tied to dynamics necessary for movement initiation, they would remain unchanged, with feedback-based changes being sufficient to retain balance following volitional arm movement. Participants executed beyond-arm reaching movements in four different postural configurations that altered the quality of the BoS. Quantification of these changes to stability did not drastically alter the tuning or timing of preparatory muscle activity despite modifications to arm and CoM trajectories necessary to complete the reaching movement. In contrast to traditional views, preparatory postural muscle activity is not always tuned for balance maintenance or even as a calculation of upcoming instability but may reflect a requirement of voluntary movement towards a pre-defined location.

Children With Developmental Coordination Disorder Show Altered Visuomotor Control During Stair Negotiation Associated With Heightened State Anxiety.

Safe stair negotiation is an everyday task that children with developmental coordination disorder (DCD) are commonly thought to struggle with. Yet, there is currently a paucity of research supporting these claims. We investigated the visuomotor control strategies underpinning stair negotiation in children with (N = 18, age = 10.50 ± 2.04 years) and without (N = 16, age = 10.94 ± 2.08 years) DCD by measuring kinematics, gaze behavior and state anxiety as they ascended and descended a staircase. A questionnaire was administered to determine parents' confidence in their child's ability to safely navigate stairs and their child's fall history (within the last year). Kinematics were measured using three-dimensional motion capture (Vicon), whilst gaze was measured using mobile eye-tracking equipment (Pupil labs). The parents of DCD children reported significantly lower confidence in their child's ability to maintain balance on the stairs and significantly more stair-related falls in the previous year compared to the parents of typically developing (TD) children. During both stair ascent and stair descent, the children with DCD took longer to ascend/descend the staircase and displayed greater handrail use, reflecting a more cautious stair negotiation strategy. No differences were observed between groups in their margin of stability, but the DCD children exhibited significantly greater variability in their foot-clearances over the step edge, which may increase the risk of a fall. For stair descent only, the DCD children reported significantly higher levels of state anxiety than the TD children and looked significantly further along the staircase during the initial entry phase, suggesting an anxiety-related response that may bias gaze toward the planning of future stepping actions over the accurate execution of an ongoing step. Taken together, our findings provide the first quantifiable evidence that (a) safe stair negotiation is a significant challenge for children with DCD, and that (b) this challenge is reflected by marked differences in their visuomotor control strategies and state anxiety levels. Whilst it is currently unclear whether these differences are contributing to the frequency of stair-related falls in children with DCD, our findings pave the way for future research to answer these important questions.

Children With Developmental Coordination Disorder Exhibit Greater Stepping Error Despite Similar Gaze Patterns and State Anxiety Levels to Their Typically Developing Peers.

This study examined stepping accuracy, gaze behavior, and state-anxiety in children with (N = 21, age M = 10.81, SD = 1.89) and without (N = 18, age M = 11.39, SD = 2.06) developmental coordination disorder (DCD) during an adaptive locomotion task. Participants walked at a self-selected pace along a pathway, placing their foot into a raised rectangular floor-based target box followed by either no obstacles, one obstacle, or two obstacles. Stepping kinematics and accuracy were determined using three-dimensional motion capture, whilst gaze was determined using mobile eye-tracking equipment. The children with DCD displayed greater foot placement error and variability when placing their foot within the target box and were more likely to make contact with its edges than their typically developing (TD) peers. The DCD group also displayed greater variability in the length and width of their steps in the approach to the target box. No differences were observed between groups in any of the gaze variables measured, in mediolateral velocity of the center of mass during the swing phase into the target box, or in the levels of self-reported state-anxiety experienced prior to facing each task. We therefore provide the first quantifiable evidence that deficits to foot placement accuracy and precision may be partially responsible for the increased incidence of trips and falls in DCD, and that these deficits are likely to occur independently from gaze behavior and state-anxiety.

Negotiating stairs with an inconsistent riser: Implications for stepping safety.

Stairs are associated with falls, especially when step dimensions are inconsistent. However, the mechanisms by which inconsistencies cause this higher risk are mostly theoretical. In this experimental study we quantified the effect of inconsistent rise heights on biomechanical measurements of stepping safety from younger (n = 26) and older adults (n = 33). In ascent, both groups decreased foot clearance (~9 mm) over the inconsistently higher step (F(1,56) = 48.4, p < 0.001). In descent, they reduced foot contact length on the higher step by 3% (F(1,56) = 9.1, p < 0.01). Reduced clearance may result in a toe-catch potentially leading to a trip, while reduced foot contact lengths increase the risk of overstepping which may also lead to a fall. These effects occurred because participants did not alter their foot trajectories, indicating they either did not detect or were not able to adjust to the inconsistent rise, increasing the likelihood of a fall. Consistent stair construction is vital, and existing inconsistencies should be identified and safety interventions developed.

Can We Accurately Measure Axial Segment Coordination during Turning Using Inertial Measurement Units (IMUs)?

Camera-based 3D motion analysis systems are considered to be the gold standard for movement analysis. However, using such equipment in a clinical setting is prohibitive due to the expense and time-consuming nature of data collection and analysis. Therefore, Inertial Measurement Units (IMUs) have been suggested as an alternative to measure movement in clinical settings. One area which is both important and challenging is the assessment of turning kinematics in individuals with movement disorders. This study aimed to validate the use of IMUs in the measurement of turning kinematics in healthy adults compared to a camera-based 3D motion analysis system. Data were collected from twelve participants using a Vicon motion analysis system which were compared with data from four IMUs placed on the forehead, middle thorax, and feet in order to determine accuracy and reliability. The results demonstrated that the IMU sensors produced reliable kinematic measures and showed excellent reliability (ICCs 0.80-0.98) and no significant differences were seen in paired t-tests in all parameters when comparing the two systems. This suggests that the IMU sensors provide a viable alternative to camera-based motion capture that could be used in isolation to gather data from individuals with movement disorders in clinical settings and real-life situations.

Stair negotiation behaviour of older individuals: Do step dimensions matter?

Stair falls are a major health problem for older people. Most studies on identification of stair fall risk factors are limited to staircases set in given step dimensions. However, it remains unknown whether the conclusions drawn would still apply if the dimensions had been changed to represent more challenging or easier step dimensions encountered in domestic and public buildings. The purpose was to investigate whether the self-selected biomechanical stepping behaviours are maintained when the dimensions of a staircase are altered. Sixty-eight older adults (>65 years) negotiated a seven-step staircase set in two step dimensions (shallow staircase: rise 15 cm, going 28 cm; steep staircase: rise 20 cm, going 25 cm). Six biomechanical outcome measures indicative of stair fall risk were measured. K-means clustering profiled the overall stair-negotiating behaviour and cluster profiles were calculated. A Cramer's V measured the degree of association in membership between clusters. The cluster profiles revealed that the biomechanically risky and conservative factors that characterized the overall behaviour in the clusters did not differ for the majority of older adults between staircases for ascent and descent. A strong association of membership between the clusters on the shallow staircase and the steep staircase was found for stair ascent (Cramer's V: 0.412, p < 0.001) and descent (Cramer's V: 0.380, p = 0.003). The findings indicate that manipulating the demand of the task would not affect the underpinning mechanism of a potential stair fall. Therefore, for most individuals, detection of stair fall risk might not require testing using a staircase with challenging step dimensions.

Optimal lighting levels for stair safety: Influence of lightbulb type and brightness on confidence, dynamic balance and stepping characteristics.

INTRODUCTION: Poor lighting has been associated with stair falls in young and older adults. However, current guidelines for illuminating stairs seem arbitrary, differ widely between sources, and are often difficult to interpret. AIMS: Here we examined the influence of real-world bulb illumination properties on stair descent safety in young and older adults, with a view to generating preliminary evidence for appropriate lightbulb use/stair illumination. METHODS: Stair tread illumination (lx) was measured in a standard UK home (2.23 m ceiling) from a low (50 W; 630 lm) and a high (103 W, 1450 lm) power compact fluorescent lamp (CFL) bulb from the time they were turned on until they reached full brightness. This enabled modelling of their illumination characteristics during warm up. Illumination was also measured from a low (40 W, 470 lm) and a high (100 W, 1521 lm) power LED bulb at first turn-on. Computer-controlled custom lighting then replicated these profiles, in addition to a Bright control (350 lx), on an instrumented staircase descended (3 × trials per light condition) by 12 young (25.3 ± 4.4 years; 5 males), 12 higher ability older (HAOA: 69.6 ± 4.7 years; 5 males) and 13 lower ability older (LAOA: 72.4 ± 4.2; 3 males) healthy adults. Older adults were allocated to ability groups based on physiological and cognitive function. Stair-specific confidence was assessed prior to the first descent in each new lighting condition, and whole-body 3D kinematics (Vicon) quantified margins of stability and foot clearances with respect to the step edges. Mixed ANOVAs examined these measures for within-subject effects of lighting (×5), between-subject effects of age (×3) and interactions between lighting and age. RESULTS: Use of CFL bulbs led to lower self-reported confidence in older adults (20.37%, p = .01), and increased margins of stability (12.47%, p = .015) and foot clearances with respect to the step edges (10.36%, p = .003). Importantly, using CFL bulbs increased foot clearance variability with respect to the bottom step (32.74%, p = .046), which is where a high proportion of falls occur. CONCLUSION: Stair-tread illumination from CFL bulbs at first turn on leads to less safe stair negotiation. We suggest high powered LED bulbs may offer a safer alternative.

A novel multivariate approach for biomechanical profiling of stair negotiation.

Stair falls, especially during stair descent, are a major problem for older people. Stair fall risk has typically been assessed by quantifying mean differences between subject groups (e.g. older vs. younger individuals) for a number of biomechanical parameters individually indicative of risk, e.g., a reduced foot clearance with respect to the stair edge, which increases the chances of a trip. This approach neglects that individuals within a particular group may also exhibit other concurrent conservative strategies that could reduce the overall risk for a fall, e.g. a decreased variance in foot clearance. The purpose of the present study was to establish a multivariate approach that characterises the overall stepping behaviour of an individual. Twenty-five younger adults (age: 24.5 ±â€¯3.3 y) and 70 older adults (age: 71.1 ±â€¯4.1 y) descended a custom-built instrumented seven-step staircase at their self-selected pace in a step-over-step manner without using the handrails. Measured biomechanical parameters included: 1) Maximal centre of mass angular acceleration, 2) Foot clearance, 3) Proportion of foot length in contact with stair, 4) Required coefficient of friction, 5) Cadence, 6) Variance of these parameters. As a conventional analysis, a one-way ANOVA followed by Bonferroni post-hoc testing was used to identify differences between younger adults, older fallers and non-fallers. To examine differences in overall biomechanical stair descent behaviours between individuals, k-means clustering was used. The conventional grouping approach showed an effect of age and fall history on several single risk factors. The multivariate approach identified four clusters. Three clusters differed from the overall mean by showing both risky and conservative strategies on the biomechanical outcome measures, whereas the fourth cluster did not display any particularly risky or conservative strategies. In contrast to the conventional approach, the multivariate approach showed the stepping behaviours identified did not contain only older adults or previous fallers. This highlights the limited predictive power for stair fall risk of approaches based on single-parameter comparisons between predetermined groups. Establishing the predictive power of the current approach for future stair falls in older people is imperative for its implementation as a falls prevention tool.

Core crystallization and pile-up in the cooling sequence of evolving white dwarfs.

White dwarfs are stellar embers depleted of nuclear energy sources that cool over billions of years1. These stars, which are supported by electron degeneracy pressure, reach densities of 107 grams per cubic centimetre in their cores2. It has been predicted that a first-order phase transition occurs during white-dwarf cooling, leading to the crystallization of the non-degenerate carbon and oxygen ions in the core, which releases a considerable amount of latent heat and delays the cooling process by about one billion years3. However, no direct observational evidence of this effect has been reported so far. Here we report the presence of a pile-up in the cooling sequence of evolving white dwarfs within 100 parsecs of the Sun, determined using photometry and parallax data from the Gaia satellite4. Using modelling, we infer that this pile-up arises from the release of latent heat as the cores of the white dwarfs crystallize. In addition to the release of latent heat, we find strong evidence that cooling is further slowed by the liberation of gravitational energy from element sedimentation in the crystallizing cores5-7. Our results describe the energy released by crystallization in strongly coupled Coulomb plasmas8,9, and the measured cooling delays could help to improve the accuracy of methods used to determine the age of stellar populations from white dwarfs10.

Gait adaptability.

Our activities of daily living inherently involve interacting with the physical environment. This interaction involves both reactive (feedback) and proactive (feedforward) gait adaptations. Reactive adaptations involve responses to mechanical perturbations and occur, for instance, when we stumble over a doorstep or slip on an icy spot on the pavement. Examples of proactive adaptations in response to visual stimuli include stepping over an obstacle, targeting precise foot placements when walking on rough terrain, stepping up to the pavement, or making a turn for going around a corner. These adaptations have to be implemented in our steady-state gait pattern, thus posing a challenge to center-of-mass control and maintenance of forward progression. Yet, despite the apparent complexity of adaptive bipedal walking, we commonly do this with remarkable ease. This chapter will provide a comprehensive overview of the behavioral strategies and control mechanisms that we apply for executing these common, yet complex, gait adaptations. In addition, how we use visual information for guiding proactive gait adaptations and path selection will be discussed. Finally, cognitive involvement during gait adaptations will also be addressed.

Do postural constraints affect eye, head, and arm coordination?

If a whole body reaching task is produced when standing or adopting challenging postures, it is unclear whether changes in attentional demands or the sensorimotor integration necessary for balance control influence the interaction between visuomotor and postural components of the movement. Is gaze control prioritized by the central nervous system (CNS) to produce coordinated eye movements with the head and whole body regardless of movement context? Considering the coupled nature of visuomotor and whole body postural control during action, this study aimed to understand how changing equilibrium constraints (in the form of different postural configurations) influenced the initiation of eye, head, and arm movements. We quantified the eye-head metrics and segmental kinematics as participants executed either isolated gaze shifts or whole body reaching movements to visual targets. In total, four postural configurations were compared: seated, natural stance, with the feet together (narrow stance), or while balancing on a wooden beam. Contrary to our initial predictions, the lack of distinct changes in eye-head metrics; timing of eye, head, and arm movement initiation; and gaze accuracy, in spite of kinematic differences, suggests that the CNS integrates postural constraints into the control necessary to initiate gaze shifts. This may be achieved by adopting a whole body gaze strategy that allows for the successful completion of both gaze and reaching goals. NEW & NOTEWORTHY Differences in sequence of movement among the eye, head, and arm have been shown across various paradigms during reaching. Here we show that distinct changes in eye characteristics and movement sequence, coupled with stereotyped profiles of head and gaze movement, are not observed when adopting postures requiring changes to balance constraints. This suggests that a whole body gaze strategy is prioritized by the central nervous system with postural control subservient to gaze stability requirements.

The effects of constraining vision and eye movements on whole-body coordination during standing turns.

Turning the body towards a new direction is normally achieved via a top-down synergy whereby gaze (eye direction in space) leads the upper body segments, which in turn lead the feet. These anticipatory eye movements are observable even in darkness and constraining the initial eye movements modifies the stereotyped top-down reorientation sequence. Our aim was to elucidate the relative contributions of vision and eye movements to whole-body coordination during large standing turns by observing the effects of separately removing visual information or suppressing eye movements throughout the turn. We predicted that constraining eye movements would modify the steering synergy, whereas removing vision would have little effect. We found that preventing eye movements modified both timing and spatial characteristics of axial segment and feet rotation. When gaze was fixed, gait initiation, but not axial segment rotation, was delayed in comparison to both full vision and no vision turns. When eye movements were prevented, the predictable relationship between the extent head rotation led the body and peak head angular velocity was abolished suggesting that anticipatory head movements normally subserve gaze behaviour. In addition, stepping frequency significantly reduced during the gaze fixation condition but not during the no-vision condition, suggesting that oculomotor control is linked to stepping behaviour.

Reduced sensitivity for visual textures affects judgments of shape-from-shading and step-climbing behaviour in older adults.

Falls on stairs are a major hazard for older adults. Visual decline in normal ageing can affect step-climbing ability, altering gait and reducing toe clearance. Here we show that a loss of fine-grained visual information associated with age can affect the perception of surface undulations in patterned surfaces. We go on to show that such cues affect the limb trajectories of young adults, but due to their lack of sensitivity, not that of older adults. Interestingly neither the perceived height of a step nor conscious awareness is altered by our visual manipulation, but stepping behaviour is, suggesting that the influence of shape perception on stepping behaviour is via the unconscious, action-centred, dorsal visual pathway.

Older adults who have previously fallen due to a trip walk differently than those who have fallen due to a slip.

Studying the relationships between centre of mass (COM) and centre of pressure (COP) during walking has been shown to be useful in determining movement stability. The aim of the current study was to compare COM-COP separation measures during walking between groups of older adults with no history of falling, and a history of falling due to tripping or slipping. Any differences between individuals who have fallen due to a slip and those who have fallen due to a trip in measures of dynamic balance could potentially indicate differences in the mechanisms responsible for falls. Forty older adults were allocated into groups based on their self-reported fall history during walking. The non-faller group had not experienced a fall in at least the previous year. Participants who had experienced a fall were split into two groups based on whether a trip or slip resulted in the fall(s). A Vicon system was used to collect full body kinematic trajectories. Two force platforms were used to measure ground reaction forces. The COM was significantly further ahead of the COP at heel strike for the trip (14.3 ± 2.7 cm) and slip (15.3 ± 1.1 cm) groups compared to the non-fallers (12.0 ± 2.7 cm). COM was significantly further behind the COP at foot flat for the slip group (-14.9 ± 3.6 cm) compared to the non-fallers (-10.3 ± 3.9 cm). At mid-swing, the COM of the trip group was ahead of the COP (0.9 ± 1.6 cm), whereas for the slip group the COM was behind the COP (-1.2 ± 2.2 cm). These results show identifiable differences in dynamic balance control of walking between older adults with a history of tripping or slipping and non-fallers.

Is the size of the useful field of view affected by postural demands associated with standing and stepping?

The useful field of view (UFOV) is the visual area from which information is obtained at a brief glance. While studies have examined the effects of increased cognitive load on the visual field, no one has specifically looked at the effects of postural control or locomotor activity on the UFOV. The current study aimed to examine the effects of postural demand and locomotor activity on UFOV performance in healthy young adults. Eleven participants were tested on three modified UFOV tasks (central processing, peripheral processing, and divided-attention) while seated, standing, and stepping in place. Across all postural conditions, participants showed no difference in their central or peripheral processing. However, in the divided-attention task (reporting the letter in central vision and target location in peripheral vision amongst distracter items) a main effect of posture condition on peripheral target accuracy was found for targets at 57° of eccentricity (p=.037). The mean accuracy reduced from 80.5% (standing) to 74% (seated) to 56.3% (stepping). These findings show that postural demands do affect UFOV divided-attention performance. In particular, the size of the useful field of view significantly decreases when stepping. This finding has important implications for how the results of a UFOV test are used to evaluate the general size of the UFOV during varying activities, as the traditional seated test procedure may overestimate the size of the UFOV during locomotor activities.

Newly acquired fear of falling leads to altered eye movement patterns and reduced stepping safety: a case study.

This opportune case study describes visual and stepping behaviours of an 87 year old female (P8), both prior to, and following two falls. Before falling, when asked to walk along a path containing two stepping guides positioned before and after an obstacle, P8 generally visually fixated the first stepping guide until after foot contact inside it. However, after falling P8 consistently looked away from the stepping guide before completing the step into it in order to fixate the upcoming obstacle in her path. The timing of gaze redirection away from the target (in relation to foot contact inside it) correlated with absolute stepping error. No differences in eyesight, cognitive function, or balance were found between pre- and post-fall recordings. However, P8 did report large increases in fall-related anxiety and reduced balance confidence, supporting previously suggested links between anxiety/increased fear or falling and maladaptive visual/stepping behaviours. The results represent a novel insight into how psychological and related behavioural factors can change in older adults following a fall, and provide a possible partial rationalisation for why recent fallers are more likely to fall again in the following 12 months. These findings highlight novel possibilities for falls prevention and rehabilitation.