Gazing into Thin Air: The Dual-Task Costs of Movement Planning and Execution during Adaptive Gait

Presentation of multiple task instructional sets impacts auditory Stroop performance during dual task locomotion

The auditory Stroop is a modification of the classic Stroop paradigm commonly used in dual-task research when the motor task requires the visual system. Despite its use, there are gaps in our understanding of this tool. For example, in visual/auditory Stroop paradigms, neutral cues irrelevant to the required response, which theoretically cause less interference/facilitation, are used to elucidate effects of visual/auditory demands on neural processes. Specifically, in auditory Stroop paradigms the use and choice of neutral cue words is inconsistent. To address these gaps, we instrumented participants with kinematic markers and a digital microphone and asked them to respond to auditory Stroop cues and neutral cue words consisting of either one or two syllables, while simultaneously performing an unobstructed locomotor task. Two blocks of trials were collected. In one block, participants had prior knowledge that either an auditory Stroop or a neutral word stimulus would be presented (Known); a second block presented both types of cognitive cues in a random order to participants (Mixed). We observed main effects of cognitive task (neutral, incongruent, congruent) and instructional set (Known, Mixed) on response times, but not on center of mass velocity. Also, more time was required to verbally respond to an incongruent compared to congruent or neutral task across all conditions, and neutral task words with one syllable resulted in longer response times compared to two syllable neutral words. We recommend that researchers include neutral cues when using the auditory Stroop test and to carefully consider their neutral word choice.

The effects of trait and state anxiety on gait in healthy young adults

Stable, personality-based (trait), and fluctuating, situational (state) anxiety have both been shown to consume attentional resources and reduce functional cognitive capacity, which may play a role in gait control. However, the role of attention in the relationship between trait and state anxiety has not yet been investigated formally. This study used a virtual reality-threat environment to evaluate whether changes in attention mediate the effects of state and trait anxiety on gait. Thirty adults aged 19-28 completed five walking trials in four conditions: (i) low threat-walking across a virtual plank (0.5 m wide) on flat ground; (ii) low threat + dual task (auditory digit monitoring); (iii) high threat-walking across a virtual plank elevated above a deep pit; and (iv) high threat + dual task. Trait anxiety levels were determined by the State-Trait Anxiety Inventory, while state anxiety was captured using self-assessment manikins. Higher trait anxiety predicted slower gait velocity and longer time in double support in the high-threat condition compared to low-threat condition (i vs iii), but not when dual tasking, compared to single-task walking, in the absence of threat (ii vs i). Additionally, higher trait anxiety predicted increased step length variability in the high compared to low-threat dual-task condition. Overall, trait anxiety predicts a slower, more cautious gait pattern during threatening conditions while dual tasking during the threat.

Patients with knee osteoarthritis have altered gait and gaze patterns compared to age-matched controls: A pilot study

PURPOSE

Although knee Osteoarthritis (KOA) sufferers are at an increased risk of falls, possibly due to impaired gait function, the associated gaze behaviour in patients with KOA are largely unknown. Thus, we compared gait and gaze behaviours characteristics between KOA patients and asymptomatic age-matched controls.

RESULTS

For Timed Up and Go (TUG) and stair climb tasks, the KOA group demonstrated longer periods of gaze fixations with less frequency of fixations compared to the control group. Conversely, for the Timed up and Go Agility (TUGA) test shorter fixation and frequency patterns were observed. The KOA group presented a shorter final stride length prior to the initiation of the first step in the Stair climb assessment. In addition, for the 30m walk and dual task assessments, the average step length was significantly shorter in the KOA group compared to controls.

CONCLUSION

Overall, we found altered gait and gaze behaviours are evident in KOA patients which could relate to their increased falls risk.

Spontaneous eye blinking during an auditory, an interoceptive and a visual task: The role of the sensory modality and the attentional focus

Previous evidence suggested that spontaneous eye blinking changes as a function of the attentional focus. In particular, eye blink rate (EBR) tends to increase when attention is directed to internal versus environmental processing. Most studies on this issue compared eye blinking during visual and mental imagery tasks, and interpreted the increase in EBR as a mechanism to focus cognitive resources on internal processing by disengaging attention from interfering information. However, since eye blinking also depends on the sensory modality of the task, the findings might be influenced by a modality-specific effect. In the present Registered Report we aim at investigating whether the environmental versus internal attentional focus can affect spontaneous blinking behaviour in non-visual tasks as well, in conditions where visual stimuli are not relevant. In a within-subject design, healthy participants performed an interoceptive task (i.e., heartbeat counting) and an auditory task in which pre-recorded heartbeats were presented aurally; during both tasks irrelevant visual stimuli were also presented. In a further control condition with the same auditory and visual stimuli, the participants were required to focus their attention on visual stimuli. Participants' EBR was recorded during each task by means of an eye-tracking system. We found that, although the interoceptive task was more difficult than the auditory and visual tasks, participants' EBR decreased by a comparable level in all tasks with respect to a rest condition, with no differences between internal versus environmental conditions. The present findings do not support the idea that EBR is modulated by an internal versus external focus of attention, at least in presence of controlled visual stimulation.

The perceived control model of falling: developing a unified framework to understand and assess maladaptive fear of falling

BACKGROUND

fear of falling is common in older adults and can have a profound influence on a variety of behaviours that increase fall risk. However, fear of falling can also have potentially positive outcomes for certain individuals. Without progressing our understanding of mechanisms underlying these contrasting outcomes, it is difficult to clinically manage fear of falling.

METHODS

this paper first summarises recent findings on the topic of fear of falling, balance and fall risk-including work highlighting the protective effects of fear. Specific focus is placed on describing how fear of falling influences perceptual, cognitive and motor process in ways that might either increase or reduce fall risk. Finally, it reports the development and validation of a new clinical tool that can be used to assess the maladaptive components of fear of falling.

RESULTS

we present a new conceptual framework-the Perceived Control Model of Falling-that describes specific mechanisms through which fear of falling can influence fall risk. The key conceptual advance is the identification of perceived control over situations that threaten one's balance as the crucial factor mediating the relationship between fear and increased fall risk. The new 4-item scale that we develop-the Updated Perceived Control over Falling Scale (UP-COF)-is a valid and reliable tool to clinically assess perceived control.

CONCLUSION

this new conceptualisation and tool (UP-COF) allows clinicians to identify individuals for whom fear of falling is likely to increase fall risk, and target specific underlying maladaptive processes such as low perceived control.

The Effect of Cognitive Task Complexity on Healthy Gait in the Walking Corsi Test

Dual-task activities are essential within everyday life, requiring visual-spatial memory (VSM) and mobility skills. Navigational memory is an important component of VSM needed to carry out everyday activities, but this is often not included in traditional tests such as the Corsi block tapping test (CBT). The Walking Corsi Test (WalCT) allows both VSM and navigational memory to be tested together, as well as allowing measures of gait to be collected, thus providing a more complete understanding of dual-task function. The aim of this study was to investigate the effect of an increasingly complex cognitive task on gait in a healthy adult population, using the WalCT and body-worn inertial measurement unit (IMU) sensors. Participants completed both the CBT and WalCT, where they were asked to replicate increasingly complex sequences until they were no longer able to carry this out correctly. IMU sensors were worn on the shins throughout the WalCT to assess changes in gait as task complexity increased. Results showed that there were significant differences in several gait parameters between completing a relatively simple cognitive task and completing a complex task. The type of memory used also appeared to have an impact on some gait variables. This indicates that even within a healthy population, gait is affected by cognitive task complexity, which may limit function in everyday dual-task activities.

Exploring how arm movement moderates the effect of task difficulty on balance performance in young and older adults

Emerging evidence highlights that arm movements exert a substantial and functionally relevant contribution on quiet standing balance control in young adults. Ageing is associated with "non-functional" compensatory postural control strategies (i.e., lower limb co-contraction), which in turn, may increase the reliance on an upper body strategy to control upright stance. Thus, the primary purpose of this study was to compare the effects of free versus restricted arm movements on balance performance in young and older adults, during tasks of different difficulty. Fifteen young (mean ± SD age; 21.3 ± 4.2 years) and fifteen older (mean ± SD age; 73.3 ± 5.0 years) adults performed bipedal, semi-tandem and tandem balance tasks under two arm position conditions: restricted arm movements and free arm movements. Centre of pressure (COP) amplitude and frequency were calculated as indices of postural performance and strategy, respectively. Especially in older adults, restriction of arm movement resulted in increased sway amplitude and frequency, which was primarily observed for the mediolateral direction. Further, increasing balance task difficulty raised the arm restriction cost (ARC; a new measure to quantify free vs. restricted arm movement differences in postural control) that was more prominent in older adults. These findings indicate the ARC provides a measure of reliance on the upper body for balance control and that arm movement is important for postural control in older adults, especially during tasks of greater difficulty.

The visual control of locomotion when stepping onto moving surfaces: A comparison of younger and older adults

Stepping between static and moving surfaces presents a locomotor challenge associated with increased injury frequency and severity in older adults. The current study evaluates younger and older adults' behaviours when overcoming challenges sampling moving walkway and escalator environments. Twelve younger adults (18-40 years, Male = 8) and 15 older adults (60-81 years, Male = 5) were examined using an integration of optoelectronic motion capture and mobile eye-tracking. Participants were investigated approaching and stepping onto a flat conveyor belt (static or moving; with or without surface (demarcation) lines). Specifically, the four conditions were: (i) static surface without demarcation lines; (ii) static surface with demarcation lines; (iii) moving surface without demarcation lines; and (iv) moving surface with demarcation lines. A two (age group) x two (surface-condition) x two (demarcation-condition) linear mixed-model revealed no main or interaction effects (p > .05) for perturbation magnitude, indicating participants maintained successful locomotion. However, different adaptive behaviours were identified between conditions with moving and accuracy demands (e.g., moving surfaces increased step length, demarcations reduced step length). Between subject effects identified differences between age groups. Older adults utilised different behaviours, such as earlier gaze transfer from the final approach walkway step location. Overall, the current study suggests that adaptive behaviours emerge relative to the environment's specific demands and the individual's action capabilities.

The effects of age and central field loss on maintaining balance control when stepping up to a new level under time-pressure

Objective

To investigate the effects of age and central field loss on the landing mechanics and balance control when stepping up to a new level under time-pressure.

Methods

Eight older individuals with age-related macular degeneration (AMD), eight visually normal older and eight visually normal younger individuals negotiated a floor-based obstacle followed by a 'step-up to a new level' task. The task was performed under (1) no-pressure; (2) time-pressure: an intermittent tone was played that increased in frequency and participants had to complete the task before the tone ceased. Landing mechanics and balance control for the step-up task was assessed with a floor-mounted force plate on the step.

Results

Increased ground reaction forces and loading rates were observed under time-pressure for young and older visual normals but not for AMD participants. Across conditions, loading rates and ground reaction forces were higher in young normals compared to older normals and AMD participants. Young visual normals also demonstrated 35-39% shorter double support times prior to and during the step-up compared to older normals and AMD participants. All groups shortened their double support times (31-40%) and single support times (7-9%) in the time-pressure compared to no-pressure condition. Regarding balance control, the centre-of-pressure displacement and velocity in the anterior-poster direction were increased under time-pressure for young and older visual normals but not for AMD participants. The centre-of-pressure displacement and velocity in the medial-lateral direction were decreased for the AMD participants under time-pressure but not for young and older visual normals.

Conclusions

Despite walking faster, AMD participants did not adapt their landing mechanics under time-pressure (i.e., they remained more cautious), whilst older and young adults with normal vision demonstrated more forceful landing mechanics with the young being most forceful. A more controlled landing might be a safety strategy to maintain balance control during the step-up, especially in time-pressure conditions when balance control in the anterior-posterior direction is more challenged.

Evaluating the integration of eye-tracking and motion capture technologies: Quantifying the accuracy and precision of gaze measures

Integrating mobile eye tracking and optoelectronic motion capture enables point of gaze to be expressed within the laboratory co-ordinate system and presents a method not commonly applied during research examining dynamic behaviors, such as locomotion. This paper examines the quality of gaze data collected through the integration. Based on research suggesting increased viewing distances are associated with reduced data quality; the accuracy and precision of gaze data as participants (N = 11) viewed floor-based targets at distances of 1–6 m was investigated. A mean accuracy of 2.55 ± 1.12° was identified, however, accuracy and precision measures (relative to targets) were significantly (p < .05) reduced at greater viewing distances. We then consider if signal processing techniques may improve accuracy and precision, and overcome issues associated with missing data. A 4th-order Butterworth lowpass filter with cut-off frequencies determined via autocorrelation did not significantly improve data quality, however, interpolation via Quintic spline was sufficient to overcome gaps of up to 0.1 s. We conclude the integration of gaze and motion capture presents a viable methodology in the study of human behavior and presents advantages for data collection, treatment, and analysis. We provide considerations for the collection, analysis, and treatment of gaze data that may help inform future methodological decisions.

Impact of dual tasking on gaze behaviour and locomotor strategies adopted while circumventing virtual pedestrians during a collision avoidance task

We investigated gaze behaviour and collision avoidance strategies in 16 healthy young individuals walking towards a goal while exposed to virtual pedestrians (VRPs) approaching from different directions (left, middle, right). This locomotor task and an auditory-based cognitive task were performed under single and dual-task conditions. Longer gaze fixation durations were observed on the approaching vs. other VRPs, with longer fixations devoted to the upper trunk and head compared to other body segments. Compared to other pedestrian approaches, the middle pedestrian received longer fixations and elicited faster walking speeds, larger onset distances of trajectory devitation and smaller obstacle clearances. Gaze and locomotor behaviours were similar between single and dual-task conditions but dual-task costs were observed for the cognitive task. The longer gaze fixations on approaching vs. other pedestrians suggest that enhanced visual attention is devoted to pedestrians posing a greater risk of collision. Likewise, longer gaze fixations for the middle pedestrians may be due to the greater collision risk entailed by this condition, and/or to the fact that this pedestrian was positioned in front of the end goal. Longer fixations on approaching VRPs' trunk and head may serve the purpose of anticipating their walking trajectory. Finally, the dual-task effects that were limited to the cognitive task suggest that healthy young adults prioritize the locomotor task and associated acquisition of visual information. The healthy patterns of visuomotor behaviour characterized in this study will serve as a basis for comparison to further understand defective collision avoidance strategies in patient populations.

Effects of multi-obstacle contexts on obstacle negotiation strategies in healthy older adults under dual-task conditions

BACKGROUND

Performance of obstacle crossing is an attentionally demanding task due to the need for motor planning and gait regulation, particularly among older adults. Despite extensive studies on age-associated changes in obstacle negotiation strategies, relatively little is known about adaptive mechanisms in the elderly regarding multiple obstacle crossings with different execution demands.

RESEARCH QUESTION

For better understanding of avoidance strategies employed by the elderly, the current study investigated adaptive mechanisms related to planning and implementation of more complex multi-obstacle contexts. Do older adults use a more conservative strategy such as prolonged step duration or elevated foot height when crossing obstacles with increased task demands of obstacle negotiation?

METHODS

Eleven healthy older and 11 young adults participated in the experiment. We examined how the presence and physical property of the second obstacle influenced the planning and adjustments for obstacle avoidance performance. Spatiotemporal characteristics of the stepping movement were analyzed using a 3D motion capture system.

RESULTS

Older adults showed a longer stance time before crossing the first obstacle than young adults when the task complexity increased. These stepping characteristics were more evident in the dual-task condition. However, their foot clearance and crossing speed were not influenced by the level of task complexity.

SIGNIFICANCE

These findings suggest that healthy elderly participants may have difficulty in developing the motor plan rather than implementing the stepping strategies under more complex obstacle constraints. A general cognitive decline with advancing age or adaptation of compensatory adjustment to enhance postural stability may underlie such altered obstacle negotiation behaviors in older adults.

Vision, cognition, and walking stability in young adults

Downward gazing is often observed when walking requires guidance. This gaze behavior is thought to promote walking stability through anticipatory stepping control. This study is part of an ongoing effort to investigate whether downward gazing also serves to enhance postural control, which can promote walking stability through a feedback/reactive mechanism. Since gaze behavior alone gives no indication as to what information is gathered and the functions it serves, we aimed to investigate the cognitive demands associated with downward gazing, as they are likely to differ between anticipatory and feedback use of visual input. To do so, we used a novel methodology to compromise walking stability in a manner that could not be resolved through modulation of stepping. Then, using interference methodology and neuroimaging, we tested for (1) interference related to dual tasking, and (2) changes in prefrontal activity. The novel methodology resulted in an increase in the time spent looking at the walking surface. Further, while some dual-task interference was observed, indicating that this gaze behavior is cognitively demanding, several gaze parameters pertaining to downward gazing and prefrontal activity correlated. These correlations revealed that a greater tendency to gaze onto the walking surface was associated with lower PFC activity, as is expected when sensory information is used through highly automatic, and useful, neural circuitry. These results, while not conclusive, do suggest that gazing onto the walking surface can be used for purposes other than anticipatory stepping control, bearing important motor-control and clinical implications.

Dual-tasking impacts gait, cognitive performance, and gaze behavior during walking in a real-world environment in older adult fallers and non-fallers

INTRODUCTION

Everyday walking often involves simultaneous performance of a cognitive task in environments with competing auditory and visual stimuli. Previous research has not evaluated task performance in these situations, where older adults are known to fall, limiting our understanding of how older adults adjust their gait, visual scanning (gaze), and cognitive processing to avoid falls (or not). The purpose of this study was to examine the effect of dual-task walking in a high-distraction real-world environment on cognitive performance, gait performance, and gaze behavior in older adult fallers relative to non-fallers.

METHODS

Fourteen community-dwelling, older adult fallers (76.6 ± 9.1 years, 11 females) and 15 community-dwelling, older adult non-fallers (77.4 ± 7.6 years, 11 females) participated. Participants performed single-task walking, single-task cognitive (seated category naming), and dual-task walking (category naming + walking) trials for 1 min each in a real-world environment (busy hospital lobby). Gait speed, stride length variability, stride duration variability, gaze fixation duration on 6 areas of interest (AOIs), and percentage of time fixating on 6 AOIs were recorded during single- and dual-task walking trials. Number of correct responses, time to first response, and mean subsequent response time (measure of rate of decline of response retrieval throughout trial) were determined for single-task cognitive and dual-task walking trials. Two-way MANCOVAs and MANOVAs were used to compare the effects of fall status and task condition on gait and cognitive variables. Hierarchical linear regression models were used to assess predictors of gaze behavior variables.

RESULTS

Compared to single-task, during dual-task trials, participants walked 0.21 m/s slower, had 1.5 fewer verbal responses, and a 2823 ms shorter mean subsequent response time, indicating a faster declining rate of retrieval during the cognitive task. Additionally, during dual-task walking, participants fixated their gaze on Far People (AOI) for a significantly smaller percentage of time and on the Near Walking Path (AOI) for a significantly greater percentage of time than during single-task walking. During all trials, being a non-faller predicted a longer average fixation duration on the Far Environment (AOI) than for fallers. Environmental busyness, baseline gait speed, and baseline executive function impacted gaze behavior.

CONCLUSION

All participants exhibited dual-task decrements in gait and cognitive performance and changes in gaze behavior from single- to dual-task walking. Perhaps of more importance, non-fallers appear to have had more freedom to divert their gaze to less relevant environmental stimuli while walking, and two measures of fall risk impacted patterns of gaze behavior differently. Thus, overt visual attention during walking in real-world environments should be further explored in relation to fall risk.

Coordination between motor and cognitive tasks in dual task gait

BACKGROUND

Dual Task (DT) paradigms are frequently used by researchers and clinicians to examine the integrity of motor processes in many movement disorders. However, the mechanism of this interaction is not fully understood. Therefore, the aim of this study was to examine the within-stride interactions between cognitive and motor processes during dual task gait (DT).

RESEARCH QUESTION

Do healthy young adults coordinate gait with secondary task processing? If so, is cognitive task processing capability associated with the coordination observed?

METHODS

Nineteen healthy young adults walked for two minutes on a motorized treadmill whilst counting backwards in sevens from three-digit numbers. The coordination of calculation verbalizations with gait parameters were assessed across six phases of the gait cycle. Mid verbalization time points (VER_Mid) were used as points of high cognitive processing of the dual task and compared with the end of the verbalizations (VER_End) as points of low cognitive processing.

RESULTS

VER_Mid and VER_End did not systematically occur in any phase of the gait cycle. However, 10/19 and 9/19 participants showed non-random distributions of verbalizations for VER_Mid and VER_End time points respectively (p < 0.01), indicating that these walkers coordinated gait with the cognitive task. Analysis of subgroups of Verbalization Coordinators and Non-Coordinators showed slower verbalization response durations (VRD) for VER_Mid Coordinators compared to VER_Mid Non-Coordinators, indicating that VER_Mid Coordinators found the cognitive tasks more demanding. No differences were found in VRD for VER_End Coordinators and VER_End Non-Coordinators.

SIGNIFICANCE

It was found that cognitive processing is coordinated with gait phases in some but not all healthy young adults during DT gait. When demands on cognitive processes are high, healthy young adults coordinate cognitive processing with phases of gait. Analysis of within-stride coordination may be of use for studying clinical conditions where gait and attentional cognition performance breaks down.

Postural Control While Walking Interferes With Spatial Learning in Older Adults Navigating in a Real Environment

Cognitive demands for postural control increase with aging and cognitive-motor interference (CMI) exists for a number of walking situations, especially with visuo-spatial cognitive tasks. Such interference also influences spatial learning abilities among older adults; however, this is rarely considered in research on aging in spatial navigation. We posited that visually and physically exploring an unknown environment may be subject to CMI for older adults. We investigated potential indicators of postural control interfering with spatial learning. Given known associations between age-related alterations in gait and brain structure, we also examined potential neuroanatomical correlates of this interference. Fourteen young and 14 older adults had to find an invisible goal in an unfamiliar, real, ecological environment. We measured walking speed, trajectory efficiency (direct route over taken route) and goal fixations (proportion of visual fixations toward the goal area). We calculated the change in walking speed between the first and last trials and adaptation indices for all three variables to quantify their modulation across learning trials. All participants were screened with a battery of visuo-cognitive tests. Eighteen of our participants (10 young, 8 older) also underwent a magnetic resonance imaging (MRI) examination. Older adults reduced their walking speed considerably on the first, compared to the last trial. The adaptation index of walking speed correlated positively with those of trajectory efficiency and goal fixations, indicating a reduction in resource sharing between walking and encoding the environment. The change in walking speed correlated negatively with gray matter volume in superior parietal and occipital regions and the precuneus. We interpret older adults’ change in walking speed as indicative of CMI, similar to dual task costs. This is supported by the correlations between the adaptation indices and between the change in walking speed and gray matter volume in brain regions that are important for navigation, given that they are involved in visual attention, sensory integration and encoding of space. These findings under ecological conditions in a natural spatial learning task question what constitutes dual tasking in older adults and they can lead future research to reconsider the actual cognitive burden of postural control in aging navigation research.

Re-evaluating the measurement and influence of conscious movement processing on gait performance in older adults: Development of the Gait-Specific Attentional Profile

BACKGROUND

Recent decades have seen increased interest in how anxiety-and associated changes in conscious movement processing (CMP)-can influence the control of balance and gait, particularly in older adults. However, the most prevalent scale used to measure CMP during gait (the Movement-Specific Reinvestment Scale (MSRS)) is generic (i.e., non-gait-specific) and potentially lacks sensitivity in this context.

METHODS

In a preliminary study, we first sought to evaluate if MSRS scores associated with the number of CMP-related thoughts self-reported by older adults while walking. The next aim was to develop and validate a new questionnaire (the Gait-Specific Attentional Profile, G-SAP) capable of measuring gait-specific CMP, in addition to other attentional processes purported to influence gait. This scale was validated using responses from 117 (exploratory) and 107 (confirmatory factor analysis) older adults, resulting in an 11-item scale with four sub-scales: CMP, anxiety, fall-related ruminations, and processing inefficiencies. Finally, in a separate cohort of 53 older adults, we evaluated associations between scores from both the G-SAP CMP subscale and the MSRS, and gait outcomes measured using a GAITRite walkway in addition to participants' fall-history.

RESULTS

MSRS scores were not associated with self-reported thoughts categorised as representing CMP. In regression analyses that controlled for functional balance, unlike the MSRS, the G-SAP subscale of CMP significantly predicted several gait characteristics including velocity (p = .033), step length (p = .032), and double-limb support (p = .015).

SIGNIFICANCE

The G-SAP provides gait-specific measures of four psychological factors implicated in mediating the control of balance and gait. In particular, unlike the MSRS, the G-SAP subscale of CMP appears sensitive to relevant attentional processes known to influence gait performance. We suggest that the G-SAP offers an opportunity for the research community to further develop understanding of psychological factors impacting gait performance across a range of applied clinical contexts.

Eye blink rate increases as a function of cognitive load during an auditory oddball paradigm

Previous evidence suggests that changes in spontaneous eye blink rate (EBR) in human adults might reflect the amount of attentional demand (i.e. cognitive load) during cognitive tasks. However, the actual direction of this relation is uncertain, since most studies investigated the role of cognitive load on EBR by employing visual tasks only. Here we aimed at elucidating the relationship between EBR and cognitive load in non-visual tasks. Sixteen healthy participants performed two auditory oddball tasks, i.e. passive listening to auditory tones versus active counting of target tones; each oddball task was immediately followed by a rest phase. Throughout the oddball tasks we assessed EBR and recorded the P300 on ERPs as an electrophysiological measure of attention. The results showed that participants' EBR increased during the active task compared to the respective rest phase. Amplitude and latency of the P300 too differed between passive and active tasks, but changes in EBR and P300 features were not correlated with each other. Our findings demonstrated that an increase in cognitive load is associated with an increase in EBR in cognitive tasks not involving visual attention. These findings are consistent with previous evidence suggesting shared neurobiological bases between attention and EBR.

Exploratory Analysis of Treading Water Coordination and the Influence of Task and Environmental Constraints

The radical embodied cognition approach to behavior requires emphasis upon how humans adapt their motor skills in response to changes in constraint. The aim of this exploratory study was to identify how the typical coordination patterns used to tread water were influenced by constraints representative of open water environments. Twenty-three participants were measured while treading water (TW) in a swimming flume in four conditions: (1) in still water, wearing a bathing suit (baseline); (2) wearing typical outdoor clothing (clothed); (3) with an additional cognitive task imposed (dual task); and (4) against a changing current (flow). Mixed methods kinematic analysis revealed four different TW coordination patterns were used across the conditions. The four TW patterns used represent a hierarchy of expertise in terms of the capacity to generate continuous lift forces, where pattern 1 (the lowest skill level) involved predominantly pushing and kicking limb movements (N = 1); pattern 2 was a movement pattern consisting of legs pushing/kicking and arms sculling (N = 7); pattern 3 was synchronous sculling of all four limbs (N = 6); and pattern 4 was the “eggbeater kick” (the highest skill level), with asynchronous sculling movements of the legs (N = 9). The four TW patterns were generally robust to the modified constraints. The higher skilled patterns (i.e., patterns 3 and 4) appeared to be the most stable coordination patterns. These results suggest that learning to perform more complex patterns to tread water might be an asset to survive in life-threatening situations.

The effects of temporal pressure on obstacle negotiation and gaze behaviour in young adults with simulated vision loss

Individuals with vision loss adapt their locomotion and gaze behaviour to safely negotiate objects in temporally unconstrained situations. However, everyday activities are often performed under time-pressure. We investigated the effects of blur on anxiety, movement kinematics and gaze behaviour during the negotiation of a floor-based obstacle under three amounts of pressure: 1) no-pressure; 2) tonal-pressure: an intermittent tone was played at a constant frequency; 3) tonal + time pressure: the intermittent tone increased in frequency and participants had to walk 20% faster to reach the end of the lab. Irrespective of the amount of pressure, the blurred vs. normal vision group reported 32% more anxiety, lifted the lead foot 43% higher and 10% slower over the obstacle, and looked 6% longer and 6% more frequently ahead of the obstacle. In the tonal + time pressure vs. no-pressure condition, both groups were more anxious, showed adaptations in movement kinematics related to walking faster, and adopted a ‘checking strategy’ by shortening their fixation durations at the obstacle. These results show that irrespective of temporal pressure, the blurred vision group remained more cautious as to how the lead foot negotiated the obstacle, in order to reduce the chance of tripping during crossing.

Using a Vibrotactile Biofeedback Device to Augment Foot Pressure During Walking in Healthy Older Adults: A Brief Report

Human movement based on sensory control is significant to motor task performance. Thus, impairments to sensory input significantly limit feedback-type motor control. The present study introduces a vibrotactile biofeedback (BF) system which augments information regarding the user’s foot pressure to enhance gait performance. The effects of the proposed system on the gait patterns of healthy older adults and on the cognitive load during gait were evaluated; these factors are essential to clarify feasibility of the device in real-life settings. The primary task of our study was to evaluate gait along with a cognitively demanding activity in 10 healthy older adults. Regarding kinematic and kinetic data in the BF condition, the subjects had significantly increased ankle dorsiflexion during the heel contact phase in the sagittal plane and marginally increased foot pressure at the toe-off and stride length. However, such kinematic and kinetic changes were not attributed to the increased walking speed. In addition, cognitive performance (i.e., the number of correct answers) was significantly decreased in participants during gait measurements in the BF condition. These data suggest that the system had the potential for modifying the kinematic and kinetic patterns during walking but not the more comprehensive walking performance in older adults. Moreover, the device appears to place a cognitive load on older adults. This short report provides crucial primary data that would help in designing successful sensory augmentation devices and further research on a BF system.

Gait characteristics of CKD patients: a systematic review

BACKGROUND

People with Chronic Kidney Disease (CKD) often present with prevalent gait impairment and high fall rates, particularly in advanced CKD stages. Gait impairment and its consequences is associated with increased hospital admission, institutionalization, and greater need for health care. The objective of this systematic review was to evaluate the quality of studies investigating CKD patients' gait characteristics at different CKD stages, to highlight areas of agreement and contradiction between studies reporting aspects of gait in CKD, and to discuss and emphasize gait parameters associated with fall risk.

METHODS

We performed a literature search of trials in CINAHL (EBSCO), Cochrane Library, EMBASE, Medline (EBSCO), PEDro, PubMed, and Scopus databases from their inception to June 30th 2018 using a two-stage process for the identification of studies. We retrieved English-, German-, Italian-, Spanish-, Portuguese and Dutch-language articles for review. Methodological quality of randomized and non-randomized studies was assessed with an adapted version of the Downs and Black checklist.

RESULTS

Thirty-one studies (22 cross-sectional with 3901 participants) and 9 longitudinal intervention studies (1 randomized control trial, 5 controlled clinical trials and 3 one-group pre-post-test; with 659 participants) were considered. The studies revealed a primary emphasis on gait speed measures within clinical tests, and a neglect of spatiotemporal gait variables. Most of the studies showed that CKD progression is associated with slowing of walking speed. No studies analysed the relation between gait parameters and fall risk.

CONCLUSIONS

There was a paucity of studies investigating aspects of gait quality in patients with CKD. In the majority of studies, only gait speed is analysed as a performance indicator. The relation between gait parameters and fall risk in CKD is not investigated. We formulate several recommendations to fill the current research gap, encourage the use of standardized gait analysis protocols that include assessment of spatiotemporal parameters in clinical care of patients with CKD, aimed at prevention of mobility decline and falls risk.

Visual scanning behavior during distracted walking in healthy young adults

BACKGROUND

An epidemic of pedestrian accidents when walking while texting suggests that people are less aware of their surroundings during distracted walking, and highlights the importance of visual scanning for pedestrian safety. Quantitative examination of visual scanning during distracted walking is still lacking.

RESEARCH QUESTION

Is visual scanning behavior altered by distracted walking in healthy young adults?

METHODS

We compared visual scanning behavior in 20 young adults during usual (single-task) walking, walking while performing a letter-fluency task, and walking while texting. Visual scanning behavior was measured by fixation count and dwell time percentage in specific areas of interest. Dual-task effects on gait speed, letter fluency, texting speed and accuracy, and situational awareness were also examined.

RESULT

Visual scanning behavior differed between the three walking conditions. During dual-task letter fluency, participants had significantly more non-walking path fixations than either of the other two conditions (i.e., more frequent, broader visual scanning). Conversely, during dual-task texting, gaze was focused predominantly on the phone, with little visual scanning of the walking path and surrounding environment. When walking without texting or talking, gaze was directed equally to far walking path and surrounding environment.

SIGNIFICANCE

Texting while walking is associated with a considerable reduction in overt visual attention to the walking path and surrounding areas. Whether this translates to reduced conscious awareness of environmental stimuli remains unclear. Performing a verbal task while walking was associated with more frequent, wider visual scanning behavior, which may be specific to the nature of the verbal task in this study.

The use of a dual-task paradigm to identify superior sensory organisation ability in rhythmic gymnasts

Previous study has showed superior sensory organisation ability in rhythmic gymnasts, but mostly in longitudinal data. With a cross-sectional design, this study used a dual-task paradigm to examine the above phenomenon. Fifteen female rhythmic gymnasts (15.0 ± 1.8 yr.) and matched peers (15.1 ± 2.1 yr.) were recruited. The Sensory Organization Test (SOT) was administered with a concurrent lower-demand (serial subtraction of three, serving as the baseline) or higher-demand (serial subtraction of seven, serving as the dual-task) arithmetic task. The results showed no main effect of group, but a group by level of arithmetic task (P = 0.001) interaction effect on SOT equilibrium score. The higher-demand task facilitated balance performance in the gymnasts, but it impeded performance in the controls, with the differences more pronounced in challenging SOT conditions. With the higher-demand task, the gymnasts adopted a sensory strategy with a higher visual ratio but a smaller somatosensory ratio compared to the controls. Better visual utilisation of sensory organisation ability was apparent in gymnasts, but only when the SOT test was performed with a higher-demand secondary task. We have demonstrated the efficacy of using the dual-task paradigm to identify the superior sensory organisation ability of adolescent rhythmic gymnasts.

Haptic-Based Perception-Empathy Biofeedback Enhances Postural Motor Learning During High-Cognitive Load Task in Healthy Older Adults

Falls and fall-induced injuries are major global public health problems, and sensory input impairment in older adults results in significant limitations in feedback-type postural control. A haptic-based biofeedback (BF) system can be used for augmenting somatosensory input in older adults, and the application of this BF system can increase the objectivity of the feedback and encourage comparison with that provided by a trainer. Nevertheless, an optimal BF system that focuses on interpersonal feedback for balance training in older adults has not been proposed. Thus, we proposed a haptic-based perception-empathy BF system that provides information regarding the older adult's center-of-foot pressure pattern to the trainee and trainer for refining the motor learning effect. The first objective of this study was to examine the effect of this balance training regimen in healthy older adults performing a postural learning task. Second, this study aimed to determine whether BF training required high cognitive load to clarify its practicability in real-life settings. Twenty older adults were assigned to two groups: BF and control groups. Participants in both groups tried balance training in the single-leg stance while performing a cognitive task (i.e., serial subtraction task). Retention was tested 24 h later. Testing comprised balance performance measures (i.e., 95% confidence ellipse area and mean velocity of sway) and dual-task performance (number of responses and correct answers). Measurements of postural control using a force plate revealed that the stability of the single-leg stance was significantly lower in the BF group than in the control group during the balance task. The BF group retained the improvement in the 95% confidence ellipse area 24 h after the retention test. Results of dual-task performance during the balance task were not different between the two groups. These results confirmed the potential benefit of the proposed balance training regimen in designing successful motor learning programs for preventing falls in older adults.

Conscious motor control impairs attentional processing efficiency during precision stepping

BACKGROUND

Current evidence suggests that fall-related anxiety can impair attentional processing efficiency during gait in both young and older adults, reducing the cognitive resources available for carrying out concurrent tasks (i.e., holding a conversation whilst walking or planning the safest route for navigation).

RESEARCH QUESTION

It has been suggested that fall-related anxiety may impair processing efficiency by directing attention 'internally', towards consciously controlling and monitoring movement. The present study aimed to evaluate this interpretation.

METHODS

Fifteen healthy young adults performed a precision stepping task during both single- and dual-task (completing the stepping task while simultaneously performing an arithmetic task), under three conditions: (1) Baseline; (2) Threat (walking on a platform raised 1.1 m above ground), and; (3) Internal focus of attention (cues/instructions to direct attention towards movement processing).

RESULTS

We observed significantly greater cognitive dual-task costs (i.e., poorer performance on the arithmetic task) during Threat compared to Baseline, with the greatest costs observed in individuals reporting the highest levels of Threat-induced conscious motor processing. Significantly greater cognitive dual-task costs were also observed during the Internal condition, confirming the assumption that consciously attending to movement reduces cognitive resources available for carrying out a secondary task during gait. These results were accompanied with significantly poorer stepping accuracy in dual-task trials during both Threat and Internal.

SIGNIFICANCE

These findings support previous attempts to rationalise attentional processing inefficiencies observed in anxious walkers as being a consequence of an anxiety-induced internal focus of attention.