Dual-task interference of reactive stepping kinematics for balance recovery strategies in older adults.

OBJECTIVE: To characterize the interference of reactive stepping kinematics related to the increase or maintenance of the number of steps in response to a large perturbation during dual tasks among older adults. METHODS: This was a cross-sectional study that included 52 community-dwelling healthy older adults. Reactive stepping performance was analyzed after forward balance loss during a single task and a second cognitive task. The number of steps taken to recover balance and dual-task interference (DTI) for muscular onset latency, anteroposterior (AP) center of pressure (COP) displacement and velocity before step initiation, and step temporal and spatial variables were measured. The DTI of the variables was compared between the participants who increased versus those who maintained the number of steps taken during the dual task relative to the single task. RESULTS: Twenty-eight (53.8 %) participants increased their steps during dual tasks relative to a single task. In older adults, the AP COP peak velocity (P < 0.001) and step length (P < 0.001) were significantly worse during dual tasks than during a single task. However, this was not observed for older adults who did not increase their steps. The DTI for the AP COP peak velocity and step length were significantly larger for the older adults who increased their steps than those who did not (AP COP peak velocity; P = 0.044, step length; P = 0.003). Both groups showed a significant muscular onset delay during dual tasks than during a single task (P < 0.001), and no significant differences were found between the groups. CONCLUSIONS: Our findings suggest that reactive stepping strategies in older adults after a large external perturbation during secondary cognitive tasks can be attributed to interference with COP control before step initiation and step length.

A Comparative Study of Cognitive and Motor Performance in Liver Recipients.

Introduction: Neurocognitive and motor impairments are often observed both before and after liver transplantation, resulting in inefficiencies in dual-task performance. Specific aim: The aim of this study was to evaluate the motor-cognitive dual-task performance in liver recipients, with a particular emphasis on cognition, performance status, and the impact of the COVID-19 pandemic. Design: A prospective, cross-sectional, web-based design with a control group was used. The study included 22 liver transplant recipients and 23 controls. Participants completed a motor-cognitive dual-task test (timed up and go test, TUG), a cognitive assessment (mini mental state examination), and a physical performance test (5-repetition sit-to-stand test). The study also used a functional performance status scale (The Karnofsky performance status) and assessed fear of coronavirus disease (fear of COVID-19 scale). Dual-task interference was assessed and the rate of correct responses per second was calculated to assess cognitive performance. Results: The results indicated no statistically significant difference in TUG time and TUG correct responses per second between the groups (group × condition interactions; P > 0.05). There was no significant difference in cognitive and motor dual-task interference during the TUG test between the two groups (P > 0.05). The Karnofsky Performance Status score was significantly correlated with TUG motor dual-task interference (r = -0.424 and P = 0.049). Conclusion: This study suggests that dual-task performance does not differ in cognitive or motor performance between liver recipients and healthy controls under the same dual-task condition. However, further controlled studies are needed to improve the generalizability of these findings.

Implicit learning provides advantage over explicit learning for gait-cognitive dual-task interference.

Dual-task performance holds significant relevance in real-world scenarios. Implicit learning is a possible approach for improving dual-task performance. Analogy learning, utilizing a single metaphor to convey essential information about motor skills, has emerged as a practical method for fostering implicit learning. However, evidence supporting the effect of implicit learning on gait-cognitive dual-task performance is insufficient. This exploratory study aimed to examine the effects of implicit and explicit learning on dual-task performance in both gait and cognitive tasks. Tandem gait was employed on a treadmill to assess motor function, whereas serial seven subtraction tasks were used to gauge cognitive performance. Thirty healthy community-dwelling older individuals were randomly assigned to implicit or explicit learning groups. Each group learned the tandem gait task according to their individual learning styles. The implicit learning group showed a significant improvement in gait performance under the dual-task condition compared with the explicit learning group. Furthermore, the implicit learning group exhibited improved dual-task interference for both tasks. Our findings suggest that implicit learning may offer greater advantages than explicit learning in acquiring autonomous motor skills. Future research is needed to uncover the mechanisms underlying implicit learning and to harness its potential for gait-cognitive dual-task performance in clinical settings.

Regional brain activity and neural network changes in cognitive-motor dual-task interference: A functional near-infrared spectroscopy study.

Previous neuroimaging studies have reported dual-task interference (DTi) and deterioration of task performance in a cognitive-motor dual task (DT) compared to that in a single task (ST). Greater frontoparietal activity is a neural signature of DTi; nonetheless, the underlying mechanism of cortical network in DTi still remains unclear. This study aimed to investigate the regional brain activity and neural network changes during DTi induced by highly demanding cognitive-motor DT. Thirty-four right-handed healthy young adults performed the spiral-drawing task. They underwent a paced auditory serial addition test (PASAT) simultaneously or independently while their cortical activity was measured using functional near-infrared spectroscopy. Motor performance was determined using the balanced integration score (BIS), a balanced index of drawing speed and precision. The cognitive task of the PASAT was administered with two difficulty levels defined by 1 s (PASAT-1 s) and 2 s (PASAT-2 s) intervals, allowing for the serial addition of numbers. Cognitive performance was determined using the percentage of correct responses. These motor and cognitive performances were significantly reduced during DT, which combined a drawing and a cognitive task at either difficulty level, compared to those in the corresponding ST conditions. The DT conditions were also characterized by significantly increased activity in the right dorsolateral prefrontal cortex (DLPFC) compared to that in the ST conditions. Multivariate Granger causality (GC) analysis of cortical activity in the selected frontoparietal regions of interest further revealed selective top-down causal connectivity from the right DLPFC to the right inferior parietal cortex during DTs. Furthermore, changes in the frontoparietal GC connectivity strength between the PASAT-2 s DT and ST conditions significantly correlated negatively with changes in the percentage of correct responses. Therefore, DTi can occur even in cognitively proficient young adults, and the right DLPFC and frontoparietal network being crucial neural mechanisms underlying DTi. These findings provide new insights into DTi and its underlying neural mechanisms and have implications for the clinical utility of cognitive-motor DTs applied to clinical populations with cognitive decline, such as those with psychiatric and brain disorders.

Increased dual-task interference during upper limb movements in stroke exceeding that found in aging - a systematic review and meta-analysis.

Objective: To determine whether dual-task interference during upper limb tasks is increased in patients after stroke compared to healthy older subjects and to compare magnitude of stroke-induced change in interference to that explained by aging. Methods: We conducted a systematic literature search in MEDLINE, CINAHL, Google Scholar and PEDro databases up to October 2023 for studies on upper limb dual-tasks in stroke and elderly healthy subjects. Eleven upper limb dual-task studies in stroke patients and 11 studies in healthy older subjects were identified and systematically reviewed. A meta-analysis was performed on seven stroke studies and on five studies in healthy older subjects that included control groups. Results: Most stroke studies investigated proximal arm movements with kinematic measures, but few studies evaluated manual dexterity. In contrast, studies in healthy older subjects used more distal (finger tapping) tasks. The meta-analysis showed that stroke patients had on average a 19% (CI 95% = 1.0-37.3) increase in dual-task interference compared to age-matched healthy controls (Z = 2.06, p = 0.04). Older healthy subjects showed greater dual-task interference compared to younger subjects (19% greater, CI 95% = 6.5-31.2, Z = 2.98, p = 0.003). Conclusion: Meta-analysis revealed an increase in dual-task interference during upper limb movements in stroke patients, exceeding age-related changes, supporting the presence of subclinical impairments in divided attention post-stroke that may impede motor recovery.

Effects of divided attention on movement-related cortical potential in community-dwelling elderly adults: A preliminary study.

Dual-tasking is defined as performing two or more tasks concurrently. This study aimed to investigate the effect of divided attention on movement-related cortical potential (MRCP) during dual-task performance in 11 community-dwelling elderly individuals while the load of the secondary task was altered. MRCP was recorded during a single task (ST), simple dual task (S-DT), and complex dual task (C-DT) as no-, low-, and high-load divided attention tasks, respectively. The ST involved self-paced tapping with an extended right index finger. In the S-DT and C-DT, the subjects simultaneously performed the ST and a visual number counting task with different levels of load. The coefficient of variation of movement frequency was significantly more variable in the C-DT than in the ST. The MRCP amplitude from electroencephalography electrode C3, contralateral to the moving hand, was significantly higher in the C-DT than in the ST. Higher attention diversion led to a significant reduction in MRCP amplitude in the participants. These results suggest that attention division in dual-task situations plays an important role in movement preparation and execution. We propose that MRCP can serve as a marker for screening the ability of older individuals to perform dual-tasks.

The Impact of Dual-Tasks and Disease Severity on Posture, Gait, and Functional Mobility among People Living with Dementia in Residential Care Facilities: A Pilot Study.

Gait speed and timed-up-and-go (TUG) predict cognitive decline, falls, and mortality. Dual-tasks may be useful in cognitive screening among people living with dementia (PWD), but more evidence is needed. This cross-sectional study aimed to compare single- and dual-task performance and determine the influence of dementia severity on dual-task performance and interference. Thirty PWD in two residential care facilities (Age: 81.3 ± 7.1 years; Montreal Cognitive Assessment: 10.4 ± 6.0 points) completed two trials of single- (feet apart) and dual-task posture (feet apart while counting backward), single- (walk 4 m) and dual-task gait (walk 4m while naming words), and single- (timed-up-and-go (TUG)), and dual-task functional mobility (TUG while completing a category task) with APDM inertial sensors. Dual-tasks resulted in greater sway frequency, jerk, and sway area; slower gait speed; greater double limb support; shorter stride length; reduced mid-swing elevation; longer TUG duration; reduced turn angle; and slower turn velocity than single-tasks (ps < 0.05). Dual-task performance was impacted (reduced double limb support, greater mid-swing elevation), and dual-task interference (greater jerk, faster gait speed) was related to moderate-to-severe compared to mild PWD. Moderate-to-severe PWD had poorer dynamic stability and a reduced ability to appropriately select a cautious gait during dual-tasks than those with mild PWD, indicating the usefulness of dual-tasks for cognitive screening.

Disturbance of information in superior parietal lobe during dual-task interference in a simulated driving task.

Performing a secondary task while driving causes a decline in driving performance. This phenomenon, called dual-task interference, can have lethal consequences. Previous fMRI studies have looked at the changes in the average brain activity to uncover the neural correlates of dual-task interference. From these results, it is unclear whether the overall modulations in brain activity result from general effects such as task difficulty, attentional modulations, and mental effort or whether it is caused by a change in the responses specific to each condition due to dual-task interference. To overcome this limitation, here, we used multi-voxel pattern analysis (MVPA) to interrogate the change in the information content in multiple brain regions during dual-task interference in simulated driving. Participants performed a lane-change task in a simulated driving environment, along with a tone discrimination task with either short or long onset time difference (Stimulus Onset Asynchrony, SOA) between the two tasks. Behavioral results indicated a robust dual-task effect on lane-change reaction time (RT). MVPA revealed regions that carry information about the driving lane-change direction (shift right/shift left), including the superior parietal lobe (SPL), visual, and motor regions. Comparison of decoding accuracies across SOA conditions in the SPL region revealed lower accuracy in the short compared to the long SOA condition. This change in accuracy was not observed in the visual and motor regions. These findings suggest that the dual-task interference in driving may be related to the disturbance of information processing in the SPL region.

Visual behavior and road traffic hazard situations when using a bike computer on a racing bike: An eye movement study.

Bike computers are an important equipment, especially on race bikes where athletes can monitor output parameters. The purpose of the present experiment was to determine the effect of visually monitoring the cadence of a bike computer and to perceive hazard traffic situations in a virtual environment. In a within subject-design individuals (N = 21) were instructed to perform the riding task in two single-task conditions (only watching the traffic at the video with occluded or without occluded bike computer), two dual-task conditions (monitoring the cadence of 70 RPM or 90 RPM and observing the traffic) and one control condition (no instructions). Percentage dwell time of the eye movements, the constant error from the target cadence, and percentage of the recognized hazard traffic situations were analyzed. The analysis indicated that the visual behavior to monitor the traffic was not reduced when individuals used a bike computer to control the cadence.

Cortical thickness is related to cognitive-motor automaticity and attention allocation in individuals with Alzheimer's disease: a regions of interest study.

Alzheimer's disease (AD) is characterized by a distinct pattern of cortical thinning and resultant changes in cognition and function. These result in prominent deficits in cognitive-motor automaticity. The relationship between AD-related cortical thinning and decreased automaticity is not well-understood. We aimed to investigate the relationship between cortical thickness regions-of-interest (ROI) and automaticity and attention allocation in AD using hypothesis-driven and exploratory approaches. We performed an ROI analysis of 46 patients with AD. Data regarding MR images, demographic characteristics, cognitive-motor dual task performance, and cognition were extracted from medical records. Cortical thickness was calculated from MR T1 images using FreeSurfer. Data from the dual task assessment was used to calculate the combined dual task effect (cDTE), a measure of cognitive-motor automaticity, and the modified attention allocation index (mAAI). Four hierarchical multiple linear regression models were conducted regressing cDTE and mAAI separately on (1) hypothesis-generated ROIs and (2) exploratory ROIs. For cDTE, cortical thicknesses explained 20.5% (p = 0.014) and 25.9% (p = 0.002) variability in automaticity in the hypothesized ROI and exploratory models, respectively. The dorsal lateral prefrontal cortex (DLPFC) (ß = - 0.479, p = 0.018) and superior parietal cortex (SPC) (ß = 0.467, p = 0.003), and were predictors of automaticity. For mAAI, cortical thicknesses explained 20.7% (p = 0.025) and 28.3% (p = 0.003) variability in attention allocation in the hypothesized ROI and exploratory models, respectively. Thinning of SPC and fusiform gyrus were associated with motor prioritization (ß = - 0.405, p = 0.013 and ß = - 0.632, p = 0.004, respectively), whereas thinning of the DLPFC was associated with cognitive prioritization (ß = 0.523, p = 0.022). Cortical thinning in AD was related to cognitive-motor automaticity and task prioritization, particularly in the DLPFC and SPC. This suggests that these regions may play a primary role in automaticity and attentional strategy during dual-tasking.

Do multimodal search cues help or hinder teleoperated search and rescue missions?

In search and rescue missions, teleoperated rovers equipped with sensor technology are deployed into harsh environments to search for targets. To support the search task, unimodal/multimodal cues can be presented via visual, acoustic and/or haptic channels. However, human operators often perform the search task in parallel with the driving task, which can cause interference of attentional resources based on multiple resource theory. Navigating corners can be a particularly challenging aspect of remote driving, as described with the Cornering Law. Therefore, search cues should not interfere with cornering. The present research explores how unimodal/multimodal search cues affect cornering performance, with typical communication delays of 50 ms and 500 ms. One-hundred thirty-one participants, distributed into two delay groups, performed a target search task with unimodal/multimodal search cues. Search cues did not interfere with cornering performance with 50 ms delays. For 500 ms delays, search cues presented via the haptic channel significantly interfered with the driving task. Practitioner summary: Teleoperated rovers can support search and rescue missions. Search cues may assist the human operator, but they may also interfere with the task of driving. The study examined interference of unimodal and multimodal search cues. Haptic cues should not be implemented for systems with a delay of 500 ms or more.

Asymmetric Influence of Dual-Task Interference on Anticipatory Postural Adjustments in One-Leg Stance.

This study investigated the differences of anticipatory postural adjustments (APAs) in a one-leg stance (OLS) that appear according to lower-extremity dominance and dual-task interference. Thirteen young, healthy, male volunteers performed the OLS task under the following six conditions: (1) dominant leg (DL), single-task; (2) DL, dual-task, with a low level of cognitive load (DT1/2); (3) DL, dual-task, with a high level of cognitive load (DT + 1); (4) non-dominant leg (NDL), single-task; (5) NDL, DT1/2; and (6) NDL, DT + 1. In order to measure the subjects' APA, we used the medial-lateral displacement of their centers of pressure and gravity from the force plate and the time-series data of joint angular motions, recorded using a 3D motion analysis system. In the NDL under the dual-task condition, the onset of APA was delayed and the amplitude declined, which resulted in an increase in the duration of the APA period. The number of components identified by principal component analysis differed according to the dominant foot, and the change caused by cognitive load was found only in the NDL. As the cognitive load increased, the variance of the principal component decreased. These findings show that dual-task interference asymmetrically influences APA according to limb dominance, which reorganizes the coordination strategy of joints' angular motion.

Dual Task Performance Is Associated with Amyloidosis in Cognitively Healthy Adults.

BACKGROUND: Preclinical Alzheimer's disease (AD) provides an opportunity for the study and implementation of interventions and strategies aimed at delaying, mitigating, and preventing AD. While this preclinical state is an ideal target, it is difficult to identify efficiently and cost-effectively. Recent findings have suggested that cognitive-motor dual task paradigms may provide additional inference. OBJECTIVES: Investigate the relationship between dual task performance and amyloidosis, suggestive of preclinical Alzheimer's disease and whether dual task performance provides additional information beyond a cognitive composite, to help in the identification of amyloidosis. DESIGN: Cross-sectional. SETTING: Outpatient specialty brain health clinical research institution in the United States. PARTICIPANTS: 52 cognitively healthy adults. MEASUREMENTS: The data included demographics, amyloid standardized uptake value ratio obtained via florbetapir-PET, neuropsychological testing, apolipoprotien E genotype, and dual task performance measures. Data were analyzed via hierarchal multiple linear regression or logistic regression, controlling for age, education, and apolipoprotien E genotype. Receiver operating characteristic curves were plotted, and sensitivity and specificity calculated via 2x2 contingency tables. RESULTS: There was a moderate relationship (rs>.30) between motor and cognitive dual task effects and amyloid standardized uptake value ratio (ps<.042). A strong relationship (r=.58) was found between combined dual task effect, a measure of automaticity derived from dual task performance, and amyloid standardized uptake value ratio (p<.001). Additionally, combined dual task effect showed promise in its unique contributions to amyloid standardized uptake value ratio, accounting for 7.8% of amyloid standardized uptake value ratio variance beyond cognitive composite scores (p=.018). Additionally, when incorporated into the cognitive composite, combined dual task effect resulted in improved diagnostic accuracy for determining elevated amyloid standardized uptake value ratio, and increased the sensitivity and specificity of the cognitive composite. CONCLUSSION: Dual task performance using the combined dual task effect, a measure of automaticity, was a moderate predictor of cerebral amyloidosis, which suggests that it has utility in the screening and diagnosis of individuals for preclinical AD. Additionally, when combined with the cognitive composite, the combined dual task effect improves diagnostic accuracy. Further research is warranted.

A Novel Way of Measuring Dual-Task Interference: The Reliability and Construct Validity of the Dual-Task Effect Battery in Neurodegenerative Disease.

BACKGROUND: Decreased automaticity is common among individuals with neurodegenerative disease and is often assessed using dual-task (DT) paradigms. However, the best methods for assessing performance changes related to DT demands remain inconclusive. OBJECTIVE: To investigate the reliability and validity of a novel battery of DT measures (DT Effect-Battery (DTE-B)) encompassing three domains: task-specific interference, task prioritization, and automaticity. METHODS: Data for this retrospective cross-sectional study included 125 participants with Parkinson's disease (PD), 127 participants with Alzheimer's disease (AD), and 84 healthy older adults. Reliability analyses were conducted using a subset of each population. DTE-B measures were calculated from single and DT performance on the Timed Up and Go test and a serial subtraction task. Construct validity was evaluated via associations within the DTE-B and with theoretically supported measures as well as known-groups validity analyses. RESULTS: Good to excellent reliability was found for DTE-B measures of task interference (motor and cognitive DT effects) (ICCs≥.658) and automaticity (combined DT effect (cDTE)) (ICCs≥.938). Evidence for convergent validity was found with associations within the hypothesized constructs. Known-groups validity analyses revealed differences in the DTE-B among the healthy group and PD and AD groups (ps≤.001), excepting task prioritization (ps≥.061). CONCLUSIONS: This study provides evidence to support the DTE-B as a reliable measure of multiple constructs pertinent to DT performance. The cDTE demonstrated evidence to support its validity as a measure of automaticity. Further investigation of the utility of the DTE-B in both PD and AD, as well as other populations, is warranted.

Dual-task interference in simulated car driving: The psychological refractory period effect when not only the second, but also the first task is ecologically relevant.

The psychological refractory period (PRP) effect denotes the finding that shortening the temporal interval between two tasks leads to increased reaction time in the second task. Earlier work in driving simulators confirmed the emergence of a PRP effect even if the second task (T2) was ecologically relevant, such as in a car-braking task. Here we evaluate the PRP effect if the first task (T1) is ecologically relevant as well. In a driving simulator, participants had to warn pedestrians against crossing the street (T1), and had to brake when the lead car braked (T2). As the temporal interval between tasks decreased, reaction time in T2 increased, confirming once more the emergence of a PRP effect. The PRP effect in our study was larger than in previous studies where T1 was artificial rather than ecologically relevant. This suggests that an ecologically relevant T1 is processed more elaborately, resulting in stronger interference with T2.

Robot-assisted gait training with auditory and visual cues in Parkinson's disease: A randomized controlled trial.

BACKGROUND: Robot-assisted gait training (RAGT) may have beneficial effects on Parkinson's disease (PD); however, the evidence to date is inconsistent. OBJECTIVES: This study compared the effects of RAGT and treadmill training (TT) on gait speed, dual-task gait performance, and changes in resting-state brain functional connectivity in individuals with PD. METHODS: In this prospective, single-center, randomized controlled trial with a parallel two-group design, 44 participants were randomly allocated to undergo 12 sessions (3 times per week for 4 weeks) of RAGT or TT. The primary outcome was gait speed on the 10-m walk test (10mWT) under comfortable walking conditions. Secondary outcomes included dual-task interference on gait speed, balance, disability scores, fear of falling, freezing of gait, and brain functional connectivity changes. All clinical outcomes were measured before (T0), immediately after (T1), and 1 month after treatment (T2). RESULTS: The mean (SD) age of the participants was 68.1 (8.1) years, and mean disease duration 108.0 (61.5) months. The groups did not significantly differ on the 10mWT (T0-T1, p = 0.726, Cohen's d = 0.133; T0-T2, p = 0.778, Cohen's d = 0.121). We observed a significant time-by-group interaction (F = 3.236, p = 0.045) for cognitive dual-task interference, controlling for confounders. After treatment, coupling was decreased to a greater extent with RAGT than TT between the visual and dorsal attention networks (p = 0.015), between bilateral fronto-parietal networks (p = 0.043), and between auditory and medial temporal networks (p = 0.018). Improvement in cognitive dual-task interference was positively correlated with enhanced visual and medial temporal network coupling overall (r = 0.386, p = 0.029) and with TT (r = 0.545, p = 0.024) but not RAGT (r = 0.151, p = 0.590). CONCLUSIONS: RAGT was not superior to intensity-matched TT on improving gait functions in individuals with PD but may be beneficial in improving gait ability under cognitive dual-task conditions. The therapeutic mechanism and key functional connectivity changes associated with improvement may differ between treatment strategies. CLINICALTRIALS: GOV: #NCT03490578.

Degree and pattern of dual-task interference during walking vary with component tasks in people after stroke: a systematic review.

QUESTIONS: What are the degree and pattern of dual-task interference during walking in people after stroke? How do these vary with disease chronicity and different component tasks in people after stroke? How does dual-task interference differ between people after stroke and people without stroke? DESIGN: Systematic review with meta-analysis of studies reporting gait-related dual-task interference. PARTICIPANTS: People after stroke and people without stroke. OUTCOME MEASURES: Measures of walking and secondary (cognitive or manual) task performance under dual-task conditions relative to those under single-task conditions. RESULTS: Seventy-six studies (2,425 people after stroke and 492 people without stroke) were included. Manual and mental tracking tasks imposed the greatest dual-task interference on gait speed, although there was substantial uncertainty in these estimates. Among mental tracking tasks, the apparently least-complex task (serial 1 subtractions) induced the greatest dual-task interference (-0.17 m/s, 95% CI -0.24 to -0.10) on gait speed, although there was substantial uncertainty in these estimates. Mutual interference (decrement in both walking and secondary component task performances during dual-tasking) was the most common dual-task interference pattern. The results of the sensitivity analyses for studies involving people with chronic stroke were similar to the results of the primary analyses. The amount of dual-task interference from a mental tracking or manual task during walking was similar between people with or without stroke. CONCLUSIONS: The degree and pattern of dual-task interference vary with the choice of component tasks. When evaluating limitations to functional mobility during dual-tasking conditions and in planning interventions accordingly, clinicians should select dual-task assessments that correspond to the daily habits and physical demands of people after stroke. REGISTRATION: CRD42017059004.

Bypassing the central bottleneck with easy tasks: Beyond ideomotor compatibility.

Maquestiaux, Lyphout-Spitz, Ruthruff, and Arexis (2020) demonstrated that ideomotor-compatible (IM) tasks (e.g., pressing the left key when an arrow points left) can operate automatically, entirely bypassing the central bottleneck that constrains dual-task performance. But is bottleneck bypassing a specific consequence of IM compatibility or is it due to task ease? To answer this question, we tested the automaticity of a task that was easy but not IM. The task was easy due to the high semantic compatibility between the stimulus and the response: saying "ping" when hearing "pong" and "pong" to "ping" in Experiment 1, saying "low" when hearing "high" and "high" to "low" in Experiment 2. We presented it as Task 2, along with a Task 1 that was not easy, due to the use of an arbitrary stimulus-response mapping. Single-task trials were randomly intermixed with dual-task trials and then used as baselines to assess dual-task costs and to simulate distributions of inter-response intervals (IRIs) predictive of bottleneck bypassing vs. bottlenecking. The results of both experiments provided converging evidence that the entire Task 2 bypassed the bottleneck on virtually all trials: very small dual-task costs, high percentages of response reversals, and a close match between the observed IRI distributions and that predicted by bottleneck bypassing. Neither ideomotor compatibility nor task speed (the semantic task was not particularly fast) explain these findings. We therefore propose that the key to bypassing the central bottleneck is the ease with which people can fully load the stimulus-response mapping into working memory.

Dual-task walking and automaticity after Stroke: Insights from a secondary analysis and imaging sub-study of a randomised controlled trial.

OBJECTIVE: To test the extent to which initial walking speed influences dual-task performance after walking intervention, hypothesising that slow walking speed affects automatic gait control, limiting executive resource availability. DESIGN: A secondary analysis of a trial of dual-task (DT) and single-task (ST) walking interventions comparing those with good (walking speed ⩾0.8 m s-1, n = 21) and limited (walking speed <0.79 m s-1, n = 24) capacity at baseline. SETTING: Community. SUBJECTS: Adults six-months post stroke with walking impairment. INTERVENTIONS: Twenty sessions of 30 minutes treadmill walking over 10 weeks with (DT) or without (ST) cognitive distraction. Good and limited groups were formed regardless of intervention received. MAIN MEASURES: A two-minute walk with (DT) and without (ST) a cognitive distraction assessed walking. fNIRS measured prefrontal cortex activation during treadmill walking with (DT) and without (ST) Stroop and planning tasks and an fMRI sub-study used ankle-dorsiflexion to simulate walking. RESULTS: ST walking improved in both groups (∆baseline: Good = 8.9 ± 13.4 m, limited = 5.3±8.9 m, Group × time = P < 0.151) but only the good walkers improved DT walking (∆baseline: Good = 10.4 ± 13.9 m, limited = 1.3 ± 7.7 m, Group × time = P < 0.025). fNIRS indicated increased ispilesional prefrontal cortex activation during DT walking following intervention (P = 0.021). fMRI revealed greater DT cost activation for limited walkers, and increased resting state connectivity of contralesional M1 with cortical areas associated with conscious gait control at baseline. After the intervention, resting state connectivity between ipsilesional M1 and bilateral superior parietal lobe, involved in integrating sensory and motor signals, increased in the good walkers compared with limited walkers. CONCLUSION: In individual who walk slowly it may be difficult to improve dual-task walking ability.Registration: ISRCTN50586966.

The Effects of Transcranial Direct Current Stimulation on Dual-Task Interference Depend on the Dual-Task Content.

Recently, some studies revealed that transcranial direct current stimulation (tDCS) reduces dual-task interference. Since there are countless combinations of dual-tasks, it remains unclear whether stable effects by tDCS can be observed on dual-task interference. An aim of the present study was to investigate whether the effects of tDCS on dual-task interference change depend on the dual-task content. We adopted two combinations of dual-tasks, i.e., a word task while performing a tandem task (word-tandem dual-task) and a classic Stroop task while performing a tandem task (Stroop-tandem dual-task). We expected that the Stroop task would recruit the dorsolateral prefrontal cortex (DLPFC) and require involvement of executive function to greater extent than the word task. Subsequently, we hypothesized that anodal tDCS over the DLPFC would improve executive function and result in more effective reduction of dual-task interference in the Stroop-tandem dual-task than in the word-tandem dual-task. Anodal or cathodal tDCS was applied over the DLPFC or the supplementary motor area using a constant current of 2.0 mA for 20 min. According to our results, dual-task interference and the task performances of each task under the single-task condition were not changed after applying any settings of tDCS. However, anodal tDCS over the left DLPFC significantly improved the word task performance immediately after tDCS under the dual-task condition. Our findings suggested that the effect of anodal tDCS over the left DLPFC varies on the task performance under the dual-task condition was changed depending on the dual-task content.