Evidence that proactive distractor suppression does not require attentional resources

Does the suppression of irrelevant visual features require attentional resources? McDonald et al. (2023, Psychonomic Bulletin & Review, 30, 224-234) proposed that suppression processes are unavailable while a person is busy performing another task. They reported the absence of the PD (believed to index suppression) when two tasks were presented close together in time. We looked for converging evidence using established behavior measures of suppression. Following McDonald et al., our participants performed a rapid serial visual presentation (RSVP) task followed by a search task. For the RSVP task, participants determined whether the target digit 4 or 6 appeared within a string of other digits. The search display appeared at a lag of 2 or 8 digits after the RSVP target. Participants searched for a yellow target circle amongst nine background circles, which included a uniquely colored distractor for some trials. The main question was whether distractor suppression would occur at Lag 2, while attentional resources were still processing the RSVP target. Suppression was assessed using the capture-probe paradigm. On 30% of trials, probe letters appeared inside the colored circles and participants reported those letters. Probe recall accuracy was lower at locations with distractor colors than those with neutral colors (the baseline), suggesting proactive suppression. Critically, this difference in probe recall accuracy was similar at Lag 2 and Lag 8, suggesting that the ability to proactively suppress distractors remains intact while dual-tasking. We argue that although reactive suppression likely requires attentional resources, proactive suppression-an implicit process-does not.

Mental fatigue does not affect static balance under both single and dual task conditions in young adults

The ability to control balance and prevent falls while carrying out daily life activities may require a predominantly controlled (cognitive) or automatic processing depending on the balance challenge, age, or other factors. Consequently, this process may be affected by mental fatigue which has been shown to impair cognitive abilities. Controlling static balance in young adults is a relatively easy task that may proceed automatically with minimal cognitive input making it insusceptible to mental fatigue. To investigate this hypothesis, static single and dual task (while concurrently counting backward by seven) balance was assessed in 60 young adults (25.2 ± 2.4 years) before and after 45 min of Stroop task (mental fatigue condition) and watching documentary (control), presented in a randomized counterbalanced order on separate days. Moreover, because mental fatigue can occur due to task underload or overload, participants carried out two different Stroop tasks (i.e., all congruent, and mainly incongruent trials) on separate days in the mental fatigue condition. Results of the study revealed a significantly higher feeling of mental fatigue after the mental fatigue conditions compared to control (p < 0.001). Similarly, the performance on congruent Stroop trials decreases with time indicating objective mental fatigue (p < 0.01). However, there was no difference in balance or concurrent task performance under both single and dual task assessments between the three conditions (p  > 0.05) indicating lack of effect of mental fatigue on static balance in this population. Therefore, future studies investigating this phenomenon in occupational or sport settings in similar population should consider using more challenging balance tasks.

Benefits of repeated alternations - Task-specific vs. task-general sequential adjustments of dual-task order control

An important cognitive requirement in multitasking is the decision of how multiple tasks should be temporally scheduled (task order control). Specifically, task order switches (vs. repetitions) yield performance costs (i.e., task-order switch costs), suggesting that task order scheduling is a vital part of configuring a task set. Recently, it has been shown that this process takes specific task-related characteristics into account: task order switches were easier when switching to a preferred (vs. non-preferred) task order. Here, we ask whether another determinant of task order control, namely the phenomenon that a task order switch in a previous trial facilitates a task order switch in a current trial (i.e., a sequential modulation of task order switch effect) also takes task-specific characteristics into account. Based on three experiments involving task order switches between a preferred (dominant oculomotor task prior to non-dominant manual/pedal task) and a non-preferred (vice versa) order, we replicated the finding that task order switching (in Trial N) is facilitated after a previous switch (vs. repetition in Trial N - 1) in task order. There was no substantial evidence in favor of a significant difference when switching to the preferred vs. non-preferred order and in the analyses of the dominant oculomotor task and the non-dominant manual task. This indicates different mechanisms underlying the control of immediate task order configuration (indexed by task order switch costs) and the sequential modulation of these costs based on the task order transition type in the previous trial.

Difficulty suppressing visual distraction while dual tasking

Human beings must often perform multiple tasks concurrently or in rapid succession. Laboratory research has revealed striking limitations in the ability to dual task by asking participants to identify two target objects that are inserted into a rapid stream of irrelevant items. Under a variety of conditions, identification of the second target (T2) is impaired for a short period of time following presentation of the first target (T1). Several theories have been developed to account for this "attentional blink" (AB), but none makes a specific prediction about how processing of T1 might impact an observer's ability to ignore a salient distractor that accompanies T2. Using event-related potentials (ERPs) to track target and distractor processing, we show that healthy young adults are capable of suppressing a salient visual-search distractor (D2) while dual tasking (as measured by the P_D component, which has been associated with suppression) but struggle to do so shortly after the appearance of T1. In fact, the impairment was more severe for distractor processing than it was for target processing (as measured by the N2pc component). Whereas, the T2-elicited N2pc was merely delayed during the AB, the distractor P_D was reduced in magnitude and was found to be statistically absent. We conclude that the inhibitory control processes that are typically engaged to prevent distraction are unavailable while an observer is busy processing a target that appeared earlier.

Age-related changes in the interference between cognitive task components and concurrent sensorimotor coordination

Continuous sensorimotor coordinations (CSCs) such as driving, walking, using control interfaces or maintaining the body's balance are often performed alongside concurrent cognitive tasks involving attention and executive function. A range of these task combinations show interference, particularly in older adults, but the timing, direction and reciprocity of interference is not yet understood at the level of the tasks' information-processing operations. This paper compares the chronometry of dual task interference between a visual oddball task and a continuous visuomanual tracking task performed by young and older adults. The oddball task's constituent operations were identified using electrophysiological correlates, and deviations in the tracking task reflected perturbations to state monitoring and adjustment characteristics of CSC tasks. Despite instructions to give equal priority to both tasks, older participants maintained a high level of resourcing of the oddball task when dual tasking whereas young participants reduced resourcing to accommodate the demands of the tracking task. Older participants had a longer period of tracking inaccuracy during the executive function component of the oddball task, and unlike in young participants, this decrement was also observed when the stimulus was not a target and the executive function of updating the target tally was not required. These detailed chronometric results clarify that age-related amplification of CSC-cognitive interference are largely due to greater inflexibility in task prioritization. Prioritization of the cognitive task over the CSC in this type of dual tasking may have safety implications in everyday task settings.

The reliability and validity of the Turkish version of the dual-task questionnaire in patients with multiple sclerosis

BACKGROUND

Activities of daily living often require performing dual-task (DT). People with Multiple Sclerosis (PwMS) may have difficulties during dual-task and these difficulties negatively affect their quality of life. However, the number of validated questionnaires to assess DT difficulties in Multiple Sclerosis (MS) is very few. Therefore, the study aimed to translate and adapt the Dual-Task Questionnaire (DTQ) into Turkish, thereafter analyzing the psychometric properties in PwMS.

METHODS

A total of 51 PwMS were recruited in the study. Cronbach's alpha coefficient was used to evaluate internal consistency. The test-retest reliability was determined using the intraclass correlation coefficient (ICC). Correlations of the DTQ with motor-dual task costs (DTCs) and cognitive-DTCs were used to assess construct validity.

RESULTS

The mean age was 36.84±10.47 years. The internal consistency of the DTQ was acceptable (α= 0.780). The test-retest reliability of all items and the total score of the DTQ were excellent (ICC>0.90). The relationships of DTQ-Total between some parameters of motor-DTCs (ρ=-0.409-(-0.495) for walking-DTCs, ρ=-0.313 for manual dexterity-DTC during mental tracking, and ρ=-0.353 for balance-DTC during mental tracking) and cognitive-DTCs (ρ=0.328 for mental tacking-DTC during balance, ρ=0.290-0.342 for all verbal fluency-DTCs) were low to moderately significant.

CONCLUSION

Turkish version of DTQ is a reliable and valid tool to measure DT difficulty in PwMS. Additionally, the questionnaire is a reliable and valid Patient Reported Outcomes Initiative for MS (PROMS) for Turkish-speaking PwMS.

Investigation of reward effects in overlapping dual-task situations

In dual-task (DT) situations, performance in reaction time and error rates decrease compared with single-task situations. These performance decrements are usually explained with the serial processing at the response selection stage constituting a bottleneck. Evidence for this assumption stems from the observation that response times for the second task (task 2; RT 2) increase with decreasing stimulus-onset asynchrony (SOA). In this study, we investigated the effect of reward on bottleneck processing in DTs. In Experiment 1, we addressed two questions. First, does reward provided for task 2 performance affect task 2 performance, or does it affect task 1 performance? To conclude whether reward affected task 2 or task 1 performance, we relied on the psychological refractory period paradigm (PRP) as a chronometric tool. Second, we asked for the locus of the reward effect within the DT stream. We demonstrated shorter RTs in task 1 in a rewarded compared with an un-rewarded condition indicating reward affected task 1 processing. Furthermore, this reward effect is propagated onto task 2 at short SOA suggesting that the locus of the reward effect can be pinpointed before or at the bottleneck of task 1. In Experiment 2, we tested for the locus of the effect propagation onto task 2. To this end, we implemented an additional difficulty manipulation of the response selection of task 2 and found that the reward effect is propagated from task 1 onto the response selection stage of task 2.

Effect of cognitive task complexity on dual task postural stability: a systematic review and meta-analysis

The dual task experimental paradigm is used to probe the attentional requirements of postural control. However, findings of dual task postural studies have been inconsistent with many studies even reporting improvement in postural stability during dual tasking and thus raising questions about cognitive involvement in postural control. A U-shaped non-linear relationship has been hypothesized between cognitive task complexity and dual task postural stability suggesting that the inconsistent results might have arisen from the use of cognitive tasks of varying complexities. To systematically review experimental studies that compared the effect of simple and complex cognitive tasks on postural stability during dual tasking, we searched seven electronic databases for relevant studies published between 1980 to September 2020. 33 studies involving a total of 1068 participants met the review's inclusion criteria, 17 of which were included in meta-analysis (healthy young adults: 15 studies, 281 participants; Stroke patients: 2 studies, 52 participants). Narrative synthesis of the findings in studies involving healthy old adults was carried out. Our result suggests that in healthy population, cognitive task complexity may not determine whether postural stability increases or decreases during dual tasking (effect of cognitive task complexity was not statistically significant; P > 0.1), and thus the U-shaped non-linear hypothesis is not supported. Rather, differential effect of dual tasking on postural stability was observed mainly based on the age of the participants and postural task challenge, implying that the involvement of cognitive resources or higher cortical functions in the control of postural stability may largely depends on these two factors.

Cognitive correlates of dual tasking costs on the timed up and go test in Parkinson disease

Introduction

Dual tasking impairments are an increasingly recognized contributor to falls in Parkinson disease (PD) and may be a promising therapeutic target for PD fall prevention trials. Depending on the context, ambulatory dual tasking difficulties may be caused by different types of neurocognitive impairments.

Methods

We performed a cross-sectional analysis of 21 participants with PD. All participants underwent detailed neuropsychological testing that was quantified using normative z-scores. All participants completed the 3-meter timed up and go test (TUG), with and without a dual tasking assignment. Biomechanistic properties of the TUG were quantified using APDM wearable OPAL sensors. We explored correlations between dual tasking cost (DTC) in 1) total TUG duration, 2) Sit-to-stand duration, 3) Stand-to-sit duration, and 4) turn velocity.

Results

Impaired total DTC in the TUG correlated inversely with global cognitive performance measured using the Montreal Cognitive Assessment (MoCA) (r = -0.4649, p = 0.0337). Sit-to-stand DTC impairments correlated inversely with processing speed on the WAIS-IV Coding (r = -0.5762, p = 0.0063), semantic fluency (r = -0.5100, p = 0.0182) and learning and memory on the Hopkins Verbal Learning Test-Revised total recall (r = -0.5502, p = 0.0098). Impaired stand-to-sit DTC function corelated inversely with visuospatial cognitive function on the Benton Judgement of Line Orientation (JOLO) test (r = -0.5181, p = 0.0161).

Conclusions

The link between dual tasking and fall risk in PD may be caused by cognitive features other than executive dysfunction and may vary based on the ambulatory task in question. These findings shed light on the cognitive contributions to falls in PD.

Integrated responding improves prospective memory accuracy

Prospective memory (PM) supports the planning and execution of future activities, and is particularly important in applied settings. We investigate a new response method that aims to improve PM accuracy by integrating the responses to an occasional PM task and a routine ongoing lexical-decision task. Instead of the most common three-choice method where the PM response replaces the ongoing response, participants were obligated to make explicit PM (present vs. absent) and ongoing (word vs. non-word) classifications on every trial through a four-choice response. Although replacement and obligatory responses were initially similar in PM accuracy, an advantage emerged with practice for the new obligatory method that was not simply due to slower responding associated with making four versus three choices. The nature of the errors differed between methods, with obligatory responding being characterised by fast PM errors and replacement by slower errors, suggesting avenues for further potential improvements in PM accuracy.

Rhyming abilities in a dual-task in school-age children who stutter

PURPOSE

We compared school-age children who stutter (CWS) and age and gender matched control participants (CWNS) in a dual-task involving a word-level rhyming task and a tone task involving pitch decisions.

METHODS

Participants were 30 children (CWS, n = 15) between 7 and 16 years. Auditory word - picture stimuli pairs from the rhyme task were categorized into nonrhyme (e.g., bear-cart), rhyme (e.g., bear-pear), and replica (e.g., bear-bear) categories. The effort associated with managing resources in the dual-task was varied through the manipulation of stimulus onset asynchrony (SOA) between the stimuli of the two tasks. Mixed methods analyses of the response time (RT, ms) and error (%) data were conducted with Group, Category, and SOA as the fixed effects and participants as the random effect. Age and phoneme awareness skills were included in the analyses.

RESULTS

More rhyming errors and a significant positive correlation between rhyming errors and age was observed in the CWS compared to the CWNS. Compared to the CWNS, a higher percentage of rhyming errors was observed in the rhyme than the nonrhyme and replica categories in the CWS in both the SOA conditions, and this effect was influenced by age and phoneme awareness skills. Analysis of the tone task data indicated that a subgroup of CWNS with higher phoneme awareness skills showed reduced RT difference between the long and the short SOA conditions thereby suggesting higher efficiency with resource allocation for dual tasking. Task-specific differences between the CWS and CWNS are interpreted to suggest limitations in the encoding of the phonological aspects of covert speech in a dual-task.

Associations between clinical characteristics and dual task performance in Multiple Sclerosis depend on the cognitive and motor dual tasks used

BACKGROUND

In persons with Multiple Sclerosis (pwMS) performing a simultaneous cognitive task while walking often results in slower gait. Clinical characteristics associated with reduced dual task (DT) performance are not yet entirely clear. This multi-centre study aimed to determine the relationship between clinical and demographical characteristics with dual task (DT) walking performance in pwMS during multiple DT conditions.

METHODS

Nine DT conditions were analysed, consisting of combinations of three types of cognitive ('digit span', 'subtraction', 'vigilance') and three types of walking ('walk', 'walk with cup', 'walk over obstacles') conditions. Primary outcomes were DT gait speed (m/s) and motor DT cost of gait speed (DTCmotor, %). Secondary outcomes were clinical tests of physical and cognitive functioning and patient-reported and demographical outcomes. Firstly, univariate analyses and, subsequently, multivariate analyses with backward modelling, were conducted for each type of walking DT condition separately. Cognitive DT conditions were included in the models as main and as interaction effect with the secondary outcomes.

RESULTS

Analysis were performed in 81 pwMS (EDSS 3.3 ± 1.0). In the final models of DTCmotor, the significant main effects were in 'walk' DT-conditions the Symbol Digit Modalities Test (SDMT), in 'cup' conditions the SDMT and Dynamic Gait Index and in 'obstacles' conditions age. For DT gait speed, main effects were found for the 2-Minute Walking Test (2MWT) and the Multiple Sclerosis Walking Scale for all walking conditions. Additionally, interactions between cognitive DT-conditions and SDMT, age and 2MWT were found.

CONCLUSION

Clinical characteristics related to DT walking performance differed according to cognitive-motor DT-condition used. Still, in general, pwMS with a better mobility demonstrated higher DT gait speed, while a faster information processing speed was related to a lower DTCmotor.

Does valence contribute to the effects of dual tasking in aversive autobiographical memory? Some unexpected findings

BACKGROUND AND OBJECTIVES

Lab experiments show that engaging in a working memory task while recalling an aversive memory reduces emotionality and vividness of memories. Studies targeting lab induced negative memory with valenced secondary tasks show promise, but work is needed on autobiographical memories to make it more in line with the original dual tasking research and PTSD treatment in clinical populations. In this study, we address this gap by evaluating differential effectiveness of valenced dual tasks on emotionality and vividness of aversive autobiographical memories.

METHODS

University students (N = 178) recalled an aversive autobiographical memory while rating either positive pictures, negative pictures, or while looking at a cross in the exposure only condition. Participants were randomized to one of three aforementioned conditions and rated their memories before and after each intervention on emotionality and vividness.

RESULTS

Against expectations, memories became more emotional and vivid regardless of condition. With regard to vividness, this effect was characterized by an interaction effect: memories became more vivid in the exposure only condition than in the combined dual tasking conditions. All effect sizes were small.

LIMITATIONS

Working memory load in the dual tasking conditions might have been insufficient.

CONCLUSIONS

The current study did not extend findings with regard to (valenced) dual tasking and revealed a possible sensitization effect of script driven autobiographical memory induction. Our study highlights the importance of aspects such as the total amount of exposure and characteristics of memory induction, specifically the addition of a script driven approach to the usual self-initiated memory activation in dual tasking research.

A mobile app to transparently distinguish single- from dual-task walking for the ecological monitoring of age-related changes in daily-life gait

BACKGROUND

Early detection of gait impairments in older adults allows the early uncovering of fall risk and/or cognitive deficits, resulting in timely interventions. Dual-task paradigms have been shown to be more sensitive than single-task conditions for the detection of subtle yet relevant gait impairments.

RESEARCH QUESTION

Can a system - encompassing a pair of instrumented insoles and a customized mobile app - transparently and accurately study ecological walking activities in single- and dual-task conditions, with the aim of detecting early and subtle age-related alterations of gait?

METHODS

The system was tested on 19 older adults during outdoor walking (two identical single-task trials and two motor-cognitive dual-task trials with the user engaged in a simple phone call and in a cognitive-demanding phone call). A single-task cognitive trial was included. Relative reliability of the gait parameters provided by the insoles during single-task walking was investigated (Intraclass Correlation Coefficient). The effect of dual tasking on both motor (Friedman test) and cognitive (Wilcoxon signed-rank test) domains was studied. To study usability, the system was tested on 5 older adults in real-life environment over 3 months.

RESULTS

Most of the parameters showed excellent reliability. Independently from the cognitive demand, walking while talking resulted in increased gait cycle and step time, with a prolonged stance phase due to an augmented double-support. Variability of gait cycle and stance phase increased only during the most demanding dual-task. Dual tasking resulted in a reduced cognitive score. Usability feedback were excellent, with users reporting to understand the usefulness of the devised system and to feel at ease when using the system and the insoles.

SIGNIFICANCE

This work paves the way toward fruitful applications of the devised system to achieve accurate and ecological monitoring of daily-life walking activities, with the final aim of detecting early and subtle alterations of gait.

Does dual-tasking provide additional value in timed "up and go" test for predicting the occurrence of falls? A longitudinal observation study by age group (young-older or old-older adults)

BACKGROUND

Previous studies using relatively large samples and longitudinal observational designs reported dual-tasking had additional value in timed "up and go" test (TUG) for falls assessment among well-functioning older adults.

AIM

To elucidate the additional value of dual-tasking in TUG for predicting the occurrence of falls among community-dwelling older adults by age group using a predictive model.

METHODS

This longitudinal observation study included 987 community-dwelling older adults at baseline. A TUG without performing another task (single-TUG) and a TUG while counting aloud backward from 100 were conducted at baseline. We computed the dual-task cost (DTC) value, which is used to quantify trends in subjects' execution of motor tests under dual-task conditions. Data on fall history were obtained using a self-administered questionnaire at the 1-year follow-up. The final analysis included 649 individuals divided into a young-older adult group (aged 60-74 years) and an old-older adult group (aged ≥ 75 years). Associations between the occurrence of falls and TUG-related values were analyzed by age group using multivariate logistic regression models.

RESULTS

For old-older adults, there were significant associations between the occurrence of falls and single-TUG time (odds ratio [OR] 1.143, 95% confidence interval [CI] 1.018-1.285) and DTC value (OR 0.981, 95% CI 0.963-0.999). No significant associations were observed for young-older adults.

CONCLUSIONS

Slower single-TUG time and lower DTC value are associated with the occurrence of falls among old-older adults but not among young-older adults. Dual tasking may provide an additional value in TUG for predicting falls among old-older adults.

No evidence for the inverted U-Curve: More demanding dual tasks cause stronger aversive memory degradation

BACKGROUND AND OBJECTIVES

Simultaneously making eye movements and recalling a memory leads to competition in working memory (WM), which reduces memory vividness and emotionality. The dose-response relationship between WM taxation and aversive memory degradation is predicted to be either linear (i.e., more cognitively demanding tasks exhibit stronger effects) or follow an inverted U-curve (i.e., there should not be too little, but also not too much taxation).

METHODS

Participants (N = 44) recalled four aversive autobiographical memories under four conditions that differed in WM taxation: complex, intermediate, simple, or no counting. Before and after each intervention, and at 24 h follow-up, participants recalled the aversive memory and rated it on vividness and unpleasantness. Using a Bayesian approach the linear and inverted U-shape relationships were directly compared.

RESULTS

Pretest to posttest drops in vividness and unpleasantness became larger with increased WM taxation of the counting conditions. There was no support for either hypotheses from pretest to follow-up for memory unpleasantness, whereas for memory vividness anecdotal evidence was found for a linear relationship.

LIMITATIONS

A reaction time (RT) task was used to select counting tasks of varying difficulties. However, the validity of this task appears to be compromised under very strenuous conditions. Higher levels of WM taxation might have been possible with more difficult counting tasks.

CONCLUSIONS

There is strong evidence for a linear dose-response relationship between WM taxation and memory degradation immediately after the intervention, and some unconvincing evidence for this pattern one day later. There was no evidence for an inverted U-curve.

Parkinson's patients delay fixations when circumventing an obstacle and performing a dual cognitive task

BACKGROUND

People with Parkinson's disease (PD) do not differ from neurologically healthy individuals in obstacle circumvention during walking, therefore they are able to use visual feedback adequately to control motor behavior in this task. However, individuals are often distracted by the secondary task when circumventing an obstacle. An increased cognitive load can require prolonged gaze fixation time on a location of interest to compensate for longer information processing duration.

RESEARCH QUESTION

To investigate the effects of cognitive dual tasking (DT) on gaze behavior during waking with obstacle circumvention in people with PD and control group, and to determine the impact of gaze behavior on motor strategy.

METHODS

Fifteen individuals with PD (PD-group) and 15 neurologically healthy individuals walked at a self-selected speed over a walkway and circumvented an obstacle centered in the walkway. The experimental conditions (5 trials each one) included obstacle circumvention without DT (OC) and obstacle circumvention with DT (OCDT). In the cognitive task, the participant mentally counted the number of times a target number appeared in an audio recording. We analyzed gaze behavior (i.e. number of gaze fixations and duration on the ground and obstacle), standard gait measures and DT cost. Two-way ANOVAs were completed for gait parameters and moment of fixation.

RESULTS

There was no significant difference in DT cost between groups and no obstacle contacts. The participants performed a longer mean duration of fixations on the ground during OCDT compared to OC. Group x condition interactions indicated that the PD-group delayed the obstacle fixation relative to the NHI for OCDT (p < 0.001) and presented greater medial-lateral body clearance (p < 0.001) and longer double support time (p < 0.001) during OCDT compared to OC.

SIGNIFICANCE

The results of this study suggest that deficits in locomotion during DT in PD-group may be caused, at least in part, by a reduced ability to fixate gaze at appropriate times during walking.

Small, movement dependent perturbations substantially alter postural control strategy in healthy young adults

Postural control is commonly investigated by observing responses to perturbations. We developed a perturbation paradigm mimicking self-generated errors in weight shifting, which are a common cause of falling among older adults. Our aim was to determine the effects of this small, but complex, perturbation on postural sway of healthy young adults and evaluate the role of vision and cognition during movement dependent perturbations. Fifteen participants stood hip-width apart with their eyes open, closed and while performing two different cognitive tasks. Participants were continuously perturbed by medial-lateral (ML) support surface translations corresponding to, and hence doubling, their own center of mass sway. We analyzed the standard deviation (SD), root mean square (RMS), range, and mean power frequency (MPF) of center of pressure displacements. ML postural sway increased due to the perturbation (SD p ≤ .001, range p < .001, RMS p ≤ .001, MPF p < .001). Cognitive load increased the ML sway range (p = .048). Lack of vision increased ML MPF (p = .001) and anterior-posterior (AP) range (p < .001), SD (p < .001), and RMS (p = .001). Significant interaction of vision with the perturbation was found for the ML range (p = .045) and AP SD (p = .018). The perturbation specifically affected ML postural sway. Increased MPF is indicative of a postural control strategy change, which was insufficient for fully controlling the increased sway. Despite being small, this type of perturbation appears to be challenging for young adults.

Is every-day walking in older adults more analogous to dual-task walking or to usual walking? Elucidating the gaps between gait performance in the lab and during 24/7 monitoring

Background

The traditional evaluation of gait in the laboratory during structured testing has provided important insights, but is limited by its “snapshot” character and observation in an unnatural environment. Wearables enable monitoring of gait in real-world environments over a week. Initial findings show that in-lab and real-world measures differ. As a step towards better understanding these gaps, we directly compared in-lab usual-walking (UW) and dual-task walking (DTW) to daily-living measures of gait.

Methods

In-lab gait features (e.g., gait speed, step regularity, and stride regularity) derived from UW and DTW were compared to the same gait features during daily-living in 150 elderly fallers (age: 76.5 ± 6.3 years, 37.6% men). In both settings, features were extracted from a lower-back accelerometer. In the real-world setting, subjects were asked to wear the device for 1 week and pre-processing detected 30-s daily-living walking bouts. A histogram of all walking bouts was determined for each walking feature for each subject and then each subject’s typical (percentile 50, median), worst (percentile 10) and the best (percentile 90) values over the week were determined for each feature. Statistics of reliability were assessed using Intra-Class correlations and Bland-Altman plots.

Results

As expected, in-lab gait speed, step regularity, and stride regularity were worse during DTW, compared to UW. In-lab gait speed, step regularity, and stride regularity during UW were significantly higher (i.e., better) than the typical daily-living values (p < 0.001) and different (p < 0.001) from the worst and best values. DTW values tended to be similar to typical daily-living values (p = 0.205, p = 0.053, p = 0.013 respectively). ICC assessment and Bland-Altman plots indicated that in-lab values do not reliably reflect the daily-walking values.

Conclusions

Gait values measured during relatively long (30-s) daily-living walking bouts are more similar to the corresponding values obtained in the lab during dual-task walking, as compared to usual walking. Still, gait performance during most daily-living walking bouts is worse than that measured during usual and dual-tasking in the lab. The values measured in the lab do not reliably reflect daily-living measures. That is, an older adult’s typical daily-living gait cannot be estimated by simply measuring walking in a structured, laboratory setting.

Changes in step time variability, not changes in step length and width, are associated with lower-trunk sway during dual-task gait in older adults

Individuals are exposed to repetitive dual-task-like situations in daily life, particularly while walking, and falls among community-dwelling older adults typically occur in such situations. Thus, understanding how individuals adapt their walking-related motion under dual-task conditions is of clinical importance. The present study was conducted to investigate the association between dual-task-related changes (DT-changes) in lower-limb gait parameters and DT-changes in lower-trunk sway. We hypothesized that DT-changes in both spatial- and temporal-lower-limb gait parameters would be associated with DT-changes in lower-trunk sway. Participants were older adults aged > 60 years who lived independently in communities (n = 43, 73.7 [6.1] years old), and younger adults (n = 28, 22.7 [5.1] years old). Participants were asked to walk while performing an additional cognitive task, or with no additional task. During walking, lower-limb gait parameters (step time, step length and width) and lower-trunk sway were measured using a photoelectric cell system and inertial sensors. In older adults, DT-changes in step time variability was significantly associated with DT-changes in lower-trunk sway (standard beta = 0.683, p = 0.003), and DT-changes in lower-trunk sway variability (standard beta = 0.493, p = 0.029). In younger adults, DT-changes in step width were significantly associated with DT-changes in lower-trunk sway (standard beta = 0.395, p = 0.041). The current results partially supported our hypotheses. The association between DT-changes in lower limb and DT-changes in lower-trunk sway varied according to age group.

Effects of dual tasking and methylphenidate on gait in children with attention deficit hyperactivity disorder

Effects of dual tasking on motor processes such as gait have been mainly investigated with healthy adults and clinical older samples whereas studies with clinical samples of children with attention deficit hyperactivity disorder (ADHD) are rare. Similarly, even though methylphenidate (MPH) is the most often prescribed medication for children with ADHD, the influence of MPH on children's gait under single-task and dual-task situations remains poorly understood. In the current study, children diagnosed with ADHD (n = 26) came twice to the laboratory, once without and once with MPH medication. They were asked to walk over an electronic walkway without a concurrent task (motor single task) and while solving different cognitive tasks (motor-cognitive dual task). Gait variability and cognitive performance were measured. Children's performance was compared to an age- and sex-matched control sample of typically developing children (n = 26) who were also tested twice. Results indicated considerable effects of dual tasking on children's gait irrespective of group (ADHD vs. controls), with children diagnosed with ADHD showing more pronounced gait alterations in dual-task situations as compared to controls. Furthermore, MPH medication in children with ADHD enabled them to substantially decrease their stride time variability to a level that was comparable to the level of typically developing children. Overall, our findings support the notion that higher cognitive processes such as attention and executive functions influence gait and that MPH can positively affect cognitive and motor processes such as gait.

Transferability and Sustainability of Motor-Cognitive Dual-Task Training in Patients with Dementia: A Randomized Controlled Trial

BACKGROUND

Specific dual-task (DT) training is effective to improve DT performance in trained tasks in patients with dementia (PwD). However, it remains an open research question whether successfully trained DTs show a transfer effect to untrained DT performances.

OBJECTIVE

To examine transfer effects and the sustainability of a specific DT training in PwD.

METHODS

One hundred and five patients with mild-to-moderate dementia (Mini-Mental State Examination: 21.9 ± 2.8 points) participated in a 10-week randomized, controlled trial. The intervention group (IG) underwent a specific DT training ("walking and counting"). The control group (CG) performed unspecific low-intensity exercise. DT performance was measured under three conditions: (1) "walking and counting" (trained); (2) "walking and verbal fluency" (semi-trained), and (3) "strength and verbal fluency" (untrained). Outcomes evaluated at baseline, after training, and 3 months after the intervention period included absolute values for the motor and cognitive performance under DT conditions, and relative DT costs (DTCs) in motor, cognitive and combined motor-cognitive performance.

RESULTS

The IG significantly improved DT performances in the trained condition for absolute motor and cognitive performance and for motor, cognitive, and combined motor-cognitive DTCs compared to the CG (p ≤ 0.001-0.047; ηp2 = 0.044-0.249). Significant transfer effects were found in the semi-trained condition for absolute motor and partly cognitive performance, and for motor but not for cognitive DTCs, and only partly for combined DTCs (p ≤ 0.001-0.041; ηp2 = 0.049-0.150). No significant transfer effects were found in the untrained condition. Three months after training cessation, DT performance in the trained condition was still elevated for most of the outcomes (p ≤ 0.001-0.038; ηp2 = 0.058-0.187). Training gains in the DT performance in the semi-trained condition were, however, not sustained, and no significant group differences were found in the DT performance in the untrained condition after the follow-up.

CONCLUSION

This study confirmed that specific DT training is effective in improving specifically trained DT performances in PwD and demonstrated sustainability of training-induced effects for at least 3 months. Effects were partially transferable to semi-trained DTs but not to untrained DTs. With increasing distance between trained and untrained DTs, transferability of training effects decreased.

The effects of dual tasking on gait synchronization during over-ground side-by-side walking

Recent studies have shown that gait synchronization during natural walking is not merely anecdotal, but it is a repeatable phenomenon that is quantifiable and is apparently related to available sensory feedback modalities. However, the mechanisms underlying this phase-locking of gait have only recently begun to be investigated. For example, it is not known what role, if any, attention plays. We employed a dual tasking paradigm in order to investigate the role attention plays in gait synchronization. Sixteen pairs of subjects walked under six conditions that manipulated the available sensory feedback and the degree of difficulty of the dual task, i.e., the attention. Movement was quantified using a trunk-mounted tri-axial accelerometer. A gait synchronization index (GSI) was calculated in order to quantify the degree of synchronization of the gait pattern. A simple dual task resulted in an increased level of synchronization, whereas a more complex dual task lead to a reduction in synchronization. Handholding increased synchronization, compared to the same attention condition without handholding. These results indicate that in order for two walkers to synchronize, some level of attention is apparently required, such that a relatively complex dual task utilizes enough attentional resources to reduce the occurrence of synchronization.

The Effects of β-Adrenergic Blockade on the Degrading Effects of Eye Movements on Negative Autobiographical Memories

BACKGROUND

Eye movement desensitization and reprocessing (EMDR) is an effective treatment for posttraumatic stress disorder. During EMDR, patients make horizontal eye movements (EMs) while simultaneously recalling a traumatic memory, which renders the memory less vivid and emotional when it is later recalled again. Recalling highly emotional autobiographical memories enhances noradrenergic neurotransmission. Noradrenaline (NA) strengthens memory (re)consolidation. However, memories become less vivid after recall+EMs. Therefore, NA might either play no significant role or serve to strengthen memories that are degraded by EMs. The present study was designed to test the latter hypothesis. We predicted that blocking NA would abolish the memory degrading effects of EMs.

METHODS

Fifty-six healthy participants selected three negative autobiographical memories. One was then recalled while making EMs, one was recalled without EMs, and one was not recalled. Vividness and emotionality of the memories as well as heart rate and skin conductance level during memory retrieval were measured before, directly after, and 24 hours after the EM task. Before the task, participants received a placebo or the noradrenergic β-receptor blocker propranolol (40 mg).

RESULTS

There were no effects of EMs on memory emotionality or psychophysiological measures in the propranolol and placebo groups. However, in the placebo group, but not in the propranolol group, memory vividness significantly decreased from pretest to posttest and follow-up after recall+EMs relative to the control conditions.

CONCLUSIONS

Blocking NA abolished the effects of EMs on the vividness of emotional memories, indicating that NA is crucial for EMDR effectiveness and possibly strengthens the reconsolidation of the degraded memory.

Apathy and higher level of gait control in normal pressure hydrocephalus

Apathy represents the most common behavioral disturbance in patients with suspicion of idiopathic normal pressure hydrocephalus (iNPH) and has a major impact on quality of life. However, its impact on gait -the hallmark motor disturbance of iNPH - has never been studied yet. This study aims to evaluate the impact of apathy on higher level of gait control in patients with suspicion of iNPH. Stride time variability (STV), a marker of higher level of gait control, was quantified during usual walking (single task) and during walking while performing simultaneously cognitive tasks (dual task) of counting and verbal fluency. Among 46 patients with suspicion of iNPH (77.6±6.7years; 34.8% women), 30 (65.2%) presented apathy (defined by a score≥14 on the Starkstein apathy scale). Backward counting induced more important worsening of STV (i.e. increasing STV) in apathetic compared to non-apathetic patients (14.8±25.1% versus 9.0±20.4%; p=0.005), while both groups presented similar executive functioning. These findings suggest that apathy contributes to gait disorders in iNPH. Apathy is easy to monitor and should be considered as a target symptom of treatment.

Evidence for capacity sharing when stopping

Research on multitasking indicates that central processing capacity is limited, resulting in a performance decrement when central processes overlap in time. A notable exception seems to be stopping responses. The main theoretical and computational accounts of stop performance assume that going and stopping do not share processing capacity. This independence assumption has been supported by many behavioral studies and by studies modeling the processes underlying going and stopping. However, almost all previous investigations of capacity sharing between stopping and going have manipulated the difficulty of the go task while keeping the stop task simple. In the present study, we held the difficulty of the go task constant and manipulated the difficulty of the stop task. We report the results of four experiments in which subjects performed a selective stop-change task, which required them to stop and change a go response if a valid signal occurred, but to execute the go response if invalid signals occurred. In the consistent-mapping condition, the valid signal stayed the same throughout the whole experiment; in the varied-mapping condition, the valid signal changed regularly, so the demands on the rule-based system remained high. We found strong dependence between stopping and going, especially in the varied-mapping condition. We propose that in selective stop tasks, the decision to stop or not will share processing capacity with the go task. This idea can account for performance differences between groups, subjects, and conditions. We discuss implications for the wider stop-signal and dual-task literature.

Effects of aging and dual tasking on step adjustments to perturbations in visually cued walking

Making step adjustments is an essential component of walking. However, the ability to make step adjustments may be compromised when the walker’s attentional capacity is limited. This study compared the effects of aging and dual tasking on step adjustments in response to stepping-target perturbations during visually cued treadmill walking. Fifteen older adults (69.4 ± 5.0 years; mean ± SD) and fifteen young adults (25.4 ± 3.0 years) walked at a speed of 3 km/h on a treadmill. Both groups performed visually cued step adjustments in response to unpredictable shifts of projected stepping targets in forward (FW), backward (BW) or sideward (SW) directions, at different levels of task difficulty [which increased as the available response distance (ARD) decreased], and with and without dual tasking (auditory Stroop task). In both groups, step adjustments were smaller than required. For FW and BW shifts, older adults undershot more under dual-task conditions. For these shifts, ARD affected the age groups differentially. For SW shifts, larger errors were found for older adults, dual tasking and the most difficult ARD. Stroop task performance did not differ between groups in all conditions. Older adults have more difficulty than young adults to make corrective step adjustments while walking, especially under dual-tasking conditions. Furthermore, they seemed to prioritize the cognitive task over the step adjustment task, a strategy that may pose aging populations at a greater fall risk. For comparable task difficulty, the older adults performed considerably worse than the young adults, indicating a decreased ability to adjust steps under time pressure.

Reliability of spatial-temporal gait parameters during dual-task interference in people with multiple sclerosis. A cross-sectional study

PURPOSE

To evaluate the reliability and minimum detectable change (MDC) of spatial-temporal gait parameters in subjects with multiple sclerosis (MS) during dual tasking.

METHOD

This cross-sectional study involved 25 healthy subjects (mean age 49.9 ± 15.8 years) and 25 people with MS (mean age 49.2 ± 11.5 years). Gait under motor-cognitive and motor-motor dual tasking conditions was evaluated in two sessions separated by a one-day interval using the GAITRite Walkway System. Test-retest reliability was assessed using intraclass correlation coefficients (ICCs), standard errors of measurement (SEM), and coefficients of variation (CV). MDC scores were computed for the velocity, cadence, step and stride length, step and stride time, double support time, the % of gait cycle for single support and stance phase, and base of support.

RESULTS

All of the gait parameters reported good to excellent ICCs under both conditions, with healthy subject values of >0.69 and MS subject values of >0.84. SEM values were always below 18% for both groups of subjects. The gait patterns of the people with MS were slightly more variable than those of the normal controls (CVs: 5.88-41.53% vs 2.84-30.48%).

CONCLUSIONS

The assessment of quantitative gait parameters in healthy subjects and people with MS is highly reliable under both of the investigated dual tasking conditions.

Effect of dual tasking on postural responses to rapid lower limb movement while seated on an exercise ball

Postural adjustments are used by the central nervous system to pre-empt and correct perturbations in balance during voluntary body movements. Alteration in these responses is associated with a number of neuromuscular/musculoskeletal conditions. Attention has been identified as important in this system; performing a concurrent cognitive task has been suggested to reduce the efficacy of this postural control. The aim of this study was to examine the effect of concurrent cognitive tasking on anticipatory postural adjustments while sitting on an exercise ball with a view to help inform future rehabilitation programmes. Bilateral EMG activity was recorded from the external and internal obliques, rectus abdominis, erector spinae and the right rectus femoris of 20 healthy subjects (9 males) with mean (SD) age of 21.88 (0.86) years (range 21-24 years). A rapid hip flexion protocol was carried out under three conditions: no concurrent task, counting out loud up from one and completing a serial sevens task. The addition of the cognitive task delayed and reduced the EMG in the prime mover muscle but had little impact on the responses of the trunk muscles within the time frame of the anticipatory responses; suggestive of a decoupling of voluntary and postural control mechanisms. The results of this study suggest that perhaps the clinical effects of dual task may not be largely due to changes in anticipatory postural adjustments. However, it would be important to compare these results to those seen in older and functionally impaired individuals as this would be more representative of the typical population undertaking such rehabilitation programmes.