How does practice reduce dual-task interference: Integration, automatization, or just stage-shortening?

Validation of fNIRS measurement of executive demand during walking with and without dual-task in younger and older adults and people with Parkinson's disease

BACKGROUND

Walking with a concurrent cognitive task (dual-task walking) can pose a challenge to some populations due to aging or neurodegenerative disease. These tasks require cognitive resources involving the prefrontal cortex and can be studied using functional near-infrared spectroscopy (fNIRS). An important step in understanding fNIRS measures during such walking tasks is validating that measures reflect the demands of the tasks and not confounding sources or movement artifacts.

AIM

This study aimed to investigate the validity of fNIRS measures of prefrontal cortex activity as an indicator of executive demand during usual walking (single-task) and dual-task walking against clinical and objective measures of motor behavior in young adults, older adults, and people with Parkinson's disease (PD), by evaluating several validation hypotheses.

METHODS

In total, 133 participants were recruited from younger adults (18-50 years, n = 42), older adults (≥60 years, n = 49) and people with PD (≥60 years, n = 42). Activity in the prefrontal cortex during walking with and without an auditory Stroop task was measured with fNIRS. A combined hemoglobin measure (correlation-based signal improvement, CBSI) was calculated for use in a region of interest analysis in the dorsolateral prefrontal cortex (dlPFC). Pre-registered hypotheses regarding convergent validity, discriminant validity and known group validity were tested. An exploratory analysis of different hemoglobin measures was also performed.

RESULTS

Increases in dlPFC activity were found from single- to dual-task walking in the younger adults group and from rest to single-task walking in the older adults and PD groups. In line with hypotheses, a positive relationship was found between between dlPFC activity during dual-task walking and dual-task cost in the younger adults group, as well as a positive relationship to step time variability during single-task walking and a negative relationship to walking speed during single-task walking in the PD group. However, several clinical and gait measures lacked a relationship with dlPFC activity.

CONCLUSION

The fNIRS results point towards the CBSI measure of dlPFC activity being a valid measure of executive demand during both single and dual-task walking. Some relationships between clinical and gait measures and brain activity during walking need further investigation.

Can frequent long stimulus onset ansynchronies (SOAs) foster the representation of two separated task-sets in dual-tasking?

Recent findings suggest that in dual-tasking the elements of the two tasks are associated across tasks and are stored in a conjoint memory episode, meaning that the tasks are not represented as isolated task-sets. In the current study, we tested whether frequent long stimulus onset ansynchronies (SOAs) can foster the representation of two separated task-sets thereby reducing or even hindering participants to generate conjoint memory episodes-compared to an integrated task-set representation induced by frequent short SOAs. Alternatively, it is conceivable that conjoint memory episodes are an inevitable consequence of presenting two tasks within a single trial. In two dual-task experiments, we tested between consecutive trials whether repeating the stimulus-response bindings of both tasks would lead to faster responses than repeating only one of the two tasks' stimulus-response bindings. The dual-task consisted of a visual-manual search task (VST) and an auditory-manual discrimination task (ADT). Overall, the results suggest that, after processing two tasks within a single trial, generating a conjoint memory episode seems to be a default process, regardless of SOA frequency. However, the respective SOA frequency affected the participants' strategy to group the processing of the two tasks or not, thereby modulating the impact of the reactivated memory episode on task performance.

Dual-task interference: Bottleneck constraint or capacity sharing? Evidence from automatic and controlled processes

This study investigated whether the interference between two tasks in dual-task processing stems from bottleneck limitations or insufficient cognitive resources due to resource sharing. Experiment 1 used tone discrimination as Task 1 and word or pseudoword classification as Task 2 to evaluate the effect of automatic versus controlled processing on dual-task interference under different SOA conditions. Experiment 2 reversed the task order. The results showed that dual-task interference persisted regardless of task type or order. Neither experiment found evidence that automatic tasks could eliminate interference. This suggests that resource limitations, rather than bottlenecks, may better explain dual-task costs. Specifically, when tasks compete for limited resources, the processing efficiency of both tasks is significantly reduced. Future research should explore how cognitive resources are dynamically allocated between tasks to better account for dual-task interference effects.

A mechanism underlying improved dual-task performance after practice: Reviewing evidence for the memory hypothesis

Extensive practice can significantly reduce dual-task costs (i.e., impaired performance under dual-task conditions compared with single-task conditions) and, thus, improve dual-task performance. Among others, these practice effects are attributed to an optimization of executive function skills that are necessary for coordinating tasks that overlap in time. In detail, this optimization of dual-task coordination skills is associated with the efficient instantiation of component task information in working memory at the onset of a dual-task trial. In the present paper, we review empirical findings on three critical predictions of this memory hypothesis. These predictions concern (1) the preconditions for the acquisition and transfer of coordination skills due to practice, (2) the role of task complexity and difficulty, and (3) the impact of age-related decline in working memory capacity on dual-task optimization.

Practice effects on dual-task order coordination and its sequential adjustment

When the performance of two tasks overlaps in time, performance impairments in one or both tasks are common. Various theoretical explanations for how component tasks are controlled in dual-task situations have been advanced. However, less attention has been paid to the issue of how two temporally overlapping tasks are appropriately coordinated in terms of their order. The current study focuses on two specific aspects of this task-order coordination: (1) the potential effects of practice on task-order coordination performance and (2) its relationships with cognitive meta-control mechanisms that adjust this coordination. These aspects were investigated in a visual-auditory dual-task combination with randomly changing task orders across trials after four sessions of dual-task practice (N = 24) and single-task practice (N = 24). The results demonstrated that task-order coordination improves during dual-task practice, and in contrast to the effects of single-task practice. Practice, on the other hand, did not show substantial evidence of an effect on the adjustment of task-order coordination. This practice-related dissociation is consistent with the assumption that (1) task-order coordination and (2) its sequential adjustment are separable sets of processes.

Effects of ultra-high field MRI environment on cognitive performance in healthy participants

INTRODUCTION

Ultra-high field MRI (UHF MRI) is rapidly becoming an essential part of our toolbox within health care and research studies; therefore, we need to get a deeper understanding of the physiological effects of ultra-high field. This study aims to investigate the cognitive performance of healthy participants in a 7 T (T) MRI environment in connection with subjectively experienced effects.

METHODS

We measured cognitive performance before and after a 1-h 7T MRI scanning session using a Digit Symbol Substitution Test (DSST) in 42 subjects. Furthermore, a computer-based survey regarding the subjectively experienced effects in connection with the MRI examination was distributed. Similarly, two DSSTs were also performed by a control group of 40 participants.

RESULTS

Even though dizziness was the strongest sensory perception in connection to the MRI scanning, we did not find any correlation between dizziness and cognitive performance. Whilst the control group improved (p=<0.001) on their second DSST the MRI group showed no significant difference (p=0.741) in the DSST before and after MRI scanning.

CONCLUSION

Transient effect on cognition after undergoing MRI scanning can't be ruled out as the expected learning effect on the DSST was not observed.

IMPLICATIONS FOR PRACTICE

Increasing understanding of the possible adverse effects may guide operators in performing UHF MRI in a safe way and with person-centered care. Furthermore, it can guide researchers in setting up research protocols to minimize confounding factors in their fMRI studies due to the transient adverse effects of the UHF environment.

Effects of HiBalance training program on physical function of individuals with idiopathic Parkinson disease: a systematic review and meta-analysis

PURPOSE

The effectiveness of the HiBalance training program for individuals with Parkinson disease (PD) remains debated, prompting a systematic investigation. This study aims to assess whether the HiBalance training program yields favorable outcomes on physical function and self-reported function measures in PD individuals.

METHODS

A systematic search across PubMed, Cochrane Library, Ovid, Scopus, and PEDro databases identified studies exploring HiBalance training's impact on physical function in idiopathic PD. Publication date restrictions were not applied. Two independent reviewers evaluated bias risk using the Cochrane Risk of Bias tool and study quality using the PEDro scale. Effect size (standardized mean difference, SMD) and heterogeneity (Higgins I2) were determined.

RESULTS

Six studies underwent qualitative analysis, with two randomized-controlled trials and one multi-center clinical trial being included in the meta-analysis. HiBalance training exhibited a significant impact on physical function (SMD = 0.49; P = 0.0003). The Mini-BESTest score and gait velocity displayed improvements with moderate-effect sizes. However, solely gait velocity showed clinical enhancement. Yet, these benefits did not remain at the 6- and 12-month follow-ups post-intervention. Self-reported function measures showed no alteration post-HiBalance training. Publication bias was absent.

CONCLUSION

HiBalance training led to clinically significant improvements solely in gait velocity, though these gains waned over time. The findings suggest the necessity of refining the HiBalance program to sustain positive outcomes and ensure lasting enhancements. This underscores the importance of post-HiBalance training exercise programs to maintain benefits in the long term.

PROSPERO REGISTRATION NUMBER

The protocol of this review and meta-analysis was registered at PROSPERO (CRD42022325649). Available from: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022325649 .

Effects of muscular and mental fatigue on spatiotemporal gait parameters in dual task walking in young, non-frail and frail older adults

BACKGROUND

Dual-task (DT) walking is of great interest in clinical evaluation to evaluate frailty or cognitive declines in older adults. Frail older adults are known to adopt different walking strategy to overcome fatigue. However, no studies evaluated the effect of muscular or mental fatigue on dual-task walking strategy and the difference between frail and non-frail older adults.

AIMS

Evaluate the effect of mental and muscular fatigue on spatio-temporal parameters in dual-task walking in young, non-frail and frail older adults.

METHODS

59 participants divided into 20 young (Y) (24.9 ± 3 years old), 20 non-frail (NF) (75.8 ± 4.9 years old) and 19 frail older adults (F) (81 ± 4.7 years old) performed single-task (ST) walking, single-task cognitive (serial subtraction of 3), and dual-task (subtraction + walking) for 1 min at their fast pace. Gait speed, step length, step length variability, stance and swing phase time, single and double support time, cadence, gait speed variability were recorded in single- and dual-task walking. The dual-task effect (DTE) was calculated as ((DT - ST)/ST) × 100). Generalized linear mixed models (GLMM) were used to compare the effects of mental and muscular fatigue on gait and cognitive variables between the groups.

RESULTS

The DTE walking parameters were worse in F compared to NF or Y but no significant effect of fatigue were highlighted except for swing time and single support time DTEs.

CONCLUSIONS

The results were mitigated but a clear difference in dual-task spatio-temporal parameters was found between F and NF which brings hope into the capacity of DT to better reveal frailty.

Dual-Task Training Effects on the Cognitive-Motor Interference in Individuals with Intellectual Disability

This study explored the effect of dual task (DT) training compared to single task (ST) training on postural and cognitive performances in DT conditions in individuals with intellectual disability (ID). Postural sways and cognitive performances were measured separately and simultaneously before and after 8 weeks in the ST training group (STTG), the DT training group (DTTG) and the control group (CG) that did not received any training. Before training, postural sways and cognitive performances were higher in the DT condition compared to ST one in all groups. After training, postural sways were higher in the DT condition compared to the ST only in the STTG and the CG. The cognitive performance increased after training only in the DTTG.

Knowledge generalization and the costs of multitasking

Humans are able to rapidly perform novel tasks, but show pervasive performance costs when attempting to do two things at once. Traditionally, empirical and theoretical investigations into the sources of such multitasking interference have largely focused on multitasking in isolation to other cognitive functions, characterizing the conditions that give rise to performance decrements. Here we instead ask whether multitasking costs are linked to the system's capacity for knowledge generalization, as is required to perform novel tasks. We show how interrogation of the neurophysiological circuitry underlying these two facets of cognition yields further insights for both. Specifically, we demonstrate how a system that rapidly generalizes knowledge may induce multitasking costs owing to sharing of task contingencies between contexts in neural representations encoded in frontoparietal and striatal brain regions. We discuss neurophysiological insights suggesting that prolonged learning segregates such representations by refining the brain's model of task-relevant contingencies, thereby reducing information sharing between contexts and improving multitasking performance while reducing flexibility and generalization. These proposed neural mechanisms explain why the brain shows rapid task understanding, multitasking limitations and practice effects. In short, multitasking limits are the price we pay for behavioural flexibility.

The Characteristics of the Reduction of Interference Effect during Dual-Task Cognitive-Motor Training Compared to a Single Task Cognitive and Motor Training in Elderly: A Randomized Controlled Trial

Many studies have indicated a weakening in several areas of cognitive functioning associated with the normal ageing process. One of the methods supporting cognitive functions in older adults is dual-task training which is based on performing cognitive and motor exercises at the same time. The study aimed at examining the characteristics of dual-task training compared to single-task training in participants over 65 years of age. Sixty-five subjects took part in the study. They were randomly assigned to three groups: dual-task cognitive-motor training (CM), single-task cognitive training (CT), and single-task motor training (MT). The training program in all groups encompassed 4 weeks and consisted of three, 30-min meetings a week. Specialized software was designed for the study. The main indicators, such as orientation and planning time and the number of errors, were monitored during the whole training in all groups. The obtained results have shown that the dual-task training was associated with a significantly greater number of movement errors, but not with a longer task planning time compared to the single-task condition training. There was a decrease in the time needed to plan a path in the mazes by subjects training in the CM, CT, and MT groups. The results indicate that after each type of training, the number of errors and the time needed to plan the path decrease, despite the increasing difficulty of the tasks. The length of planning time was strongly correlated with the number of errors made by individuals in the CM group (r = 0.74, p = 0.04), compared to the ST group-for which the said correlation was not significant (r = 0.7, p = 0.06). The dual-task cognitive-motor training is more cognitively demanding compared to the single-task cognitive and motor training. It manifests in a greater number of errors, but it does not extend the orientation and planning time.

Effects of multi-task training on motor and cognitive performances in multiple sclerosis patients without clinical disability: a single-blinded randomized controlled trial

OBJECTIVE

This study aimed to investigate the effects of multi-task training on motor and cognitive performance in People with Multiple Sclerosis (PwMS) without clinical disability compared to single-task training and a control group.

METHODS

A total of 42 patients were randomly assigned to three groups labeled as Multi-Task Training Group (MTTG, n:14), Single-Task Training Group (STTG, n:14), and Control Group (CG, n:14). The STTG performed only motor tasks based on the task-oriented training program twice a week for 6 weeks while the MTTG performed the same tasks concurrently with additional motor and cognitive tasks. The CG performed relaxation exercises at home. Postural stability by posturography, walking by Timed Up-and-Go, manual dexterity by Nine-Hole Peg Test, mental tracking by Counting Backward, and verbal fluency by Word List Generation were assessed before and after the intervention under single and dual-task conditions.

RESULTS

In the MTTG, both single cognitive and single motor task performances increased, and, moreover, the cognitive Dual-Task Costs (DTCs) decreased although the motor DTCs were not changed significantly. There were significant group-by-time interactions in favor of MTTG only on the mental tracking DTC during walking compared to the STTG. Moreover, the changes in postural and walking DTCs were associated with changes in single-motor task performance.

CONCLUSION

This study suggests that multi-task training is effective in reducing cognitive DTC rather than motor DTC under dual-task conditions in PwMS without clinical disability.

TRIAL REGISTRATION NUMBER

NCT03512886.

When more is less: Adding action effects to reduce crosstalk between concurrently performed tasks

Dual-task costs are thought to reflect the architecture of the cognitive processes that guide voluntary action. Thus, manipulations that affect dual-task costs can provide insight into how we represent and select behavior as well as allow us to better design machines and controls for safer, more efficient performance. This line of research has revealed that the sensory events that follow the responses (i.e., action effects) can affect dual-task performance even though the sensory events occur after the actions are produced. The present study assessed three hypotheses regarding how action effects impact dual-task performance: a monitoring bottleneck, central stage shortening, and crosstalk. Across two experiments, we manipulated the content of two concurrently-performed tasks: a visual task that used either spatial or nonspatial stimuli (Experiment 1) and an auditory task that used responses with or without experimentally-induced auditory action effects (Experiments 1 and 2). In Experiment 1, dual-task costs were reduced when experimentally-induced auditory action effects were present, independent of the content of the visual task. In Experiment 2, the dual-task costs depended on the content of the experimentally-induced action effects, such that costs were larger when action effects emphasized ordinal (number) information, which overlapped with the unmanipulated action effects from the visual spatial task. Strikingly, dual-task costs were reduced when added, post-response events supported greater separation between task representations relative to when no post-response events were added. These results support the crosstalk hypothesis, as action effects appear to alter task representations so that they emphasize different types of information, reducing the degree of crosstalk.

Effect of combining eight weeks of neuromuscular training with dual cognitive tasks on landing mechanics in futsal players with knee ligament dominance defect: a randomized controlled trial

Background

The performing of jump and landing in futsal simultaneous with divided attention is one of the most common mechanisms of non-contact anterior cruciate ligament (ACL) injury. Neuromuscular training has effectively reduced the risk of ACL injury, but the effect of neurocognitive training has received less attention. This study investigated the effect of combining 8 weeks of neuromuscular training with dual cognitive tasks on the landing mechanics of futsal players with knee ligament dominance defects.

Methods

Thirty male futsal players (mean ± SD: age: 21.86 ± 3.27 years) with knee ligament dominance defects were purposefully identified by the tuck jump test and were randomly divided into the intervention and the control group. The intervention group performed dual task (DT) training for three weekly sessions for 8 weeks and 60 min each, while the control group only did activities of daily living. During the drop vertical jump test, 2D landing kinematics in two moments of initial contact (IC) and full flexion (FF) were assessed. Data were analyzed by means of 2 × 2 repeated measures ANOVA followed by post hoc comparison (Bonferroni) at the significance level of (α ≤ 0.05).

Results

A significant improvement was observed in the intervention group compared to the control group for the dynamic knee valgus at IC (F1,28 = 6.33; P = 0.02, ES = 0.31) and FF (F1,28 = 13.47; P = 0.003, ES = 0.49), knee flexion at IC (F1,28 = 20.08; P = 0.001, ES = 0.41) and FF (F1,28 = 13.67; P = 0.001, ES = 0.32), ankle dorsiflexion at IC (F1,28 = 37.17; P = 0.001, ES = 0.72) and FF (F1,28 = 14.52; P = 0.002, ES = 0.50), and trunk flexion at FF (F1,28 = 20.48; P = 0.001, ES = 0.59) angles. Changes in the trunk flexion at IC (F1,28 = 0.54; P = 0.47, ES = 0.03) and trunk lateral flexion at IC (F1,28 = 0.006; P = 0.93, ES = 0.00) and FF (F1,28 = 2.44; P = 0.141, ES = 0.148) angles were not statistically significant.

Conclusions

DT training compared to the control group improved landing mechanics in futsal players with knee ligament dominance defects.

Trial registration: Current Controlled Trials using the IRCT website with ID number IRCT20210602051477N1 prospectively registered on 20/06/2021.

The effect of different dual tasks conditions on gait kinematics and spatio-temporal walking parameters in older adults

BACKGROUND

Dual-task (DT) walking has increasingly been investigated over the last decade because of its valuable role as a clinical marker of both cognitive impairment and fall risk in older adults based on cognitive and motor performance (DTEcog, DTEmotor). However, there is still a lack of information on what type of dual task to choose and which is the most adapted to the population of interest.

RESEARCH QUESTION

To evaluate the effect of different dual-tasks (DT3, DT7, FLU, STROOP) on the spatiotemporal and kinematic parameters of hip, knee, and ankle joints.

METHODS

Thirty-eight older adults were recruited (9 men, 29 women, mean age = 77.5 +/- 6.5 years, mean height = 163.6 +/- 8.6 cm, mean weight = 67.5 +/- 15.3 kg). They performed a single and dual-task walk with the 4 types of tasks during 1 min, equipped with an inertial system. Dual-task effect (DTE) on spatiotemporal and kinematic variables as well as cognitive score and speed were calculated.

RESULTS

An alteration in most of the spatiotemporal parameters was observed in each DT condition (p < 0.05), especially in arithmetic tasks (DT3, DT7), while no DT effect was noticed on kinematic parameters (RMSE<3°) except on hip and knee angular velocities (RMSE>15°). Arithmetic tasks seemed to alter more spatiotemporal and kinematic parameters than the verbal fluency or STROOP test. However, DT7 appeared to be too difficult for the population of interest.

SIGNIFICANCE

Arithmetic tasks seemed to be very pertinent as a clinical dual-task protocol for older adults. The use of an inertial system to retrieve kinematic variables is an improvement in these dual-task protocols.

Response modalities and the cognitive architecture underlying action control: Intra-modal trumps cross-modal action coordination

Performing two actions at the same time usually hampers performance. Previous studies have demonstrated a strong impact of the particular effector systems on performance in multiple action control situations. However, an open question is whether performance is generally better or worse in situations in which two actions within the same effector system are coordinated (intra-modal actions: e.g., two pedal or two manual actions) compared to situations requiring two different effector systems (cross-modal actions: e.g., a manual combined with a vocal action). Performance differences can be predicated, among others, in the light of encapsulation accounts. Encapsulation of modules on the output side of processing would suggest that actions in two different modules can be triggered simultaneously without significant interference between the actions. Thus, cross-modal actions should lead to better performance compared to intra-modal actions. We investigated this issue in two basic experiments, in which participants responded to a single stimulus (thereby maximizing control over input and central processing stages) with one or two either intra-modal or cross-modal responses (manual-manual vs. manual-oculomotor/manual-vocal in Experiment 1/2, respectively). The results represent clear evidence for a performance advantage of intra-modal over cross-modal action control across both effector system combinations and independent of the particular spatial compatibility relation between responses. The results suggest performance benefits by taking advantage of integrated, holistic representations of intra-modal action compounds.

Short-term pre-exposure to modality mappings: Modality-incompatible single-task exposure reduces modality-specific between-task crosstalk in task-switching

Modality compatibility refers to the similarity of the stimulus modality and the modality of the sensory-response effect that the response produces (i.e., vocal responses produce auditory effects). In this study, we investigated the effect of short-term pre-exposure of modality compatibility in task-switching. To this end, participants were exposed to either modality-compatible (visual-manual and auditory-vocal) or modality-incompatible (visual-vocal and auditory-manual) single-tasks. After a short-term single-task pre-exposure (with either both modality-compatible tasks, 2 × 80 trials each, or both modality-incompatible tasks, 2 × 80 trials each), participants were transferred to a task-switching situation, where they switched between tasks in both a modality-compatible and an incompatible condition. We found that after pre-exposure to modality-compatible single-tasks the typical effect of modality compatibility was found (i.e., larger switch costs with modality-incompatible tasks compared to modality-compatible tasks). In contrast, after pre-exposed to modality-incompatible single-tasks, modality compatibility no longer influenced switch costs. We assume that long-term modality-compatible associations could be overridden by short-term, task-specific associations to reduce between-task crosstalk.

EXPRESS: Are there Associations between Daily Multitasking Experience and Multitasking Performance?

Research showed mixed findings regarding the relationships between daily multitasking experience and laboratory multitasking performance. One measurement issue was the low reliability and validity of using a single measurement for daily multitasking experience. Another measurement issue was the popular use of simple laboratory paradigms that may or may not capture well cognitive processes underlying real-life multitasking. The current study revisited the relationship between daily multitasking experience and multitasking performance with a better design. Multiple measurements were used to ensure good reliability and validity. This included a mobile phone task switching measurement - an arguably better proxy for daily multitasking experience and three realistic multitasking paradigms that mimic real life multitasking situations. The results showed that (1) phone switching was not significantly associated with the media multitasking index, suggesting that they were measuring different aspects of multitasking experience; (2) indicators of the multitasking performance were moderately correlated among themselves, suggesting that different realistic multitasking paradigms were measuring overlapping multitasking abilities; and, intriguingly, (3) no significant association between multitasking experience and performance indicators was found. One possibility is that people can only benefit from daily multitasking practice when they engaged in daily multitasking activities with an intention to improve the performance. Other possibilities and implications were also discussed.

The Effect of 2 Different Dual-Task Balance Training Methods on Balance and Gait in Older Adults: A Randomized Controlled Trial

OBJECTIVE

The purpose of this study was to compare the effects of integrated and consecutive cognitive dual-task balance training in older adults on balance, fear of falling, and gait performance.

METHODS

Fifty-eight participants (age >65 years) were randomly assigned to an integrated dual-task training group (IDTT) (n = 29) and consecutive dual-task training group (CDTT) (n = 29). Balance exercises and cognitive tasks were performed simultaneously by the IDTT group and consecutively by the CDTT group for 8 weeks. Balance was assessed using the Berg Balance Scale as a primary outcome measure and the Timed "Up & Go" Test (TUG) (standard-cognitive), fear of falling was assessed using the Tinetti Falls Efficacy Scale, and gait speed was assessed using the 10-Meter Walk Test (10MWT) (under single-task and dual-task conditions). All tests were performed before and after the training.

RESULTS

There was no difference in group-time interaction in the Berg Balance Scale, TUG-standard, 10MWT-single task, and 10MWT-dual task tests. Group-time interaction was different in the TUG-cognitive and Tinetti Falls Efficacy Scale scores. Also, the effect of time was significantly different in all scales except for the 10MWT-single task in both groups.

CONCLUSION

At the end of the 8-week training period, the impact of integrated and consecutive dual-task balance training on balance and gait performance in older adults was not statistically significantly different. This study suggests that consecutive dual-task balance training can be used as an alternative method to increase balance performance and gait speed in older adults who cannot perform integrated dual-task activities.

IMPACT

There were no significant differences between the effects of the 2 dual-task training methods on balance and gait speed, suggesting that the consecutive dual-task balance training method can be used to improve the balance and gait of older adults. CDTT can be performed safely and considered as an alternative method for use in many rehabilitation training programs with older adults who cannot perform simultaneous activities.

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.

Effects of balance exercises during daily tooth brushing on balance performance in healthy children

BACKGROUND

It has been shown that supervised balance training is effective in improving balance performance in children but relatively costly in terms of personnel, materials, and time. Integrating balance exercises into daily routines such as tooth brushing reduces these needs, but its effectiveness is unknown.

OBJECTIVE

This study investigated the impact of balance exercises performed during daily tooth brushing on measures of static and dynamic balance in healthy children.

METHODS

Fifty-five healthy children were assigned to either an intervention (n = 32, age: 9.5 ± 0.7 years) or a control (n = 23, age: 9.2 ± 0.5 years) group. Participants of the intervention group performed progressive balance exercises while tooth brushing on a daily basis (2 sessions per day × 3 min per session) for eight weeks. Static (i.e., timed one-legged stance test [OLS]) and dynamic (i.e., Lower Quarter Y Balance test [YBT-LQ]) balance were tested before and after the intervention period.

RESULTS

The adherence rate to exercise was 98% for the participants of the intervention group. Significant test × group interactions in favor of the intervention group were detected in three out of four OLS stance conditions and for all YBT-LQ reach directions.

CONCLUSIONS

Eight weeks of balance exercises while tooth brushing proved to be feasible (i.e., high adherence rate) and effective (i.e., enhanced static and dynamic balance performance) and is thus recommended to improve postural control in healthy children.

Deciding while moving: Cognitive interference biases value-based decisions

When people act, they repeatedly have to make value-based decisions about the further course of actions. For example, when driving on the highway, they must decide whether to overtake other cars by changing lanes to arrive at their destination quicker; concurrently, they are required to stay on their momentary lane by controlling the steering wheel. Embodied choice models predict that concurrent action execution modulates value-based decisions. Here, we examined whether value-based decisions are influenced by a change of action costs and/or cognitive interference between concurrent actions and decision making. In a novel, computerized multilane tracking task paradigm, participants (N = 50) controlled a cursor moving on one of three horizontal lanes. During tracking (concurrent action), participants had to switch to other lanes to avoid obstacles or collect rewards (value-based decisions). The action costs associated with a lane switch depended on the cursor position relative to the currently tracked lane, and this relationship varied between conditions. Results showed that value-based lane switching decisions were biased by the cursor state. While this influence was partly attributed to minimizing action costs, a considerable part of the influence could be attributed to cognitive interference. Our findings provide further evidence for embodied choice models, showing that both cognitive interference as well as action costs bias value-based decisions.

Motor sequence learning in a goal-directed stepping task in persons with multiple sclerosis: a pilot study

Motor sequence learning in persons with multiple sclerosis (pwMS) and healthy controls (HC) under implicit or explicit learning conditions has not yet been investigated in a stepping task. Given the prevalent cognitive and mobility impairments in pwMS, this is important in order to understand motor learning processes and optimize rehabilitation strategies. Nineteen pwMS (the Expanded Disability Status Scale = 3.4 ± 1.2) and 18 HC performed a modified serial reaction time task by stepping as fast as possible on a stepping tile when it lit up, either with (explicit) or without (implicit) knowledge of the presence of a sequence beforehand. Motor sequence learning was studied by examining response time changes and differences between sequence and random blocks during the learning session (acquisition), 24 h later (retention), and in three dual-task (DT) conditions at baseline and retention (automaticity) using subtracting sevens, verbal fluency, and vigilance as concurrent cognitive DTs. Response times improved and were lower for the sequenced compared with the random blocks at the post- and retention tests (P's < 0.001). Response times during DT conditions improved after learning, but DT cost improved only for the subtracting sevens DT condition. No differences in learning were observed between learning conditions or groups. This study showed motor sequence learning, by acquisition and retention, in a stepping task in pwMS with motor impairments, to a similar degree as HC and regardless of learning conditions. Whether automaticity increased remains unclear.

Rationalizing constraints on the capacity for cognitive control

Humans are remarkably limited in: (i) how many control-dependent tasks they can execute simultaneously, and (ii) how intensely they can focus on a single task. These limitations are universal assumptions of most theories of cognition. Yet, a rationale for why humans are subject to these constraints remains elusive. This feature review draws on recent insights from psychology, neuroscience, and machine learning, to suggest that constraints on cognitive control may result from a rational adaptation to fundamental, computational dilemmas in neural architectures. The reviewed literature implies that limitations in multitasking may result from a trade-off between learning efficacy and processing efficiency and that limitations in the intensity of commitment to a single task may reflect a trade-off between cognitive stability and flexibility.

Cognitive and motor task performance under single- and dual-task conditions: effects of consecutive versus concurrent practice

The concurrent execution of two or more tasks simultaneously results in performance decrements in one or both conducted tasks. The practice of dual-task (DT) situations has been shown to decrease performance decrements. The purpose of this study was to investigate the effects of consecutive versus concurrent practice on cognitive and motor task performance under single-task (ST) and DT conditions. Forty-five young adults (21 females, 24 males) were randomly assigned to either a consecutive practice (INT consecutive) group, a concurrent practice (INT concurrent) group or a control (CON) group (i.e., no practice). Both INT groups performed 2 days of acquisition, i.e., practicing a cognitive and a motor task either consecutively or concurrently. The cognitive task required participants to perform an auditory stroop task and the number of correct responses was used as outcome measure. In the motor task, participants were asked to stand on a stabilometer and to keep the platform as close to horizontal as possible. The time in balance was calculated for further analysis. Pre- and post-practice testing included performance assessment under ST (i.e., cognitive task only, motor task only) and DT (i.e., cognitive and motor task simultaneously) test conditions. Pre-practice testing revealed no significant group differences under ST and DT test conditions neither for the cognitive nor the motor task measure. During acquisition, both INT groups improved their cognitive and motor task performance. The post-practice testing showed significantly better cognitive and motor task values under ST and DT test conditions for the two INT groups compared to the CON group. Further comparisons between the two INT groups revealed better motor but not cognitive task values in favor of the INT consecutive practice group (ST: p = 0.022; DT: p = 0.002). We conclude that consecutive and concurrent practice resulted in better cognitive (ST condition) and motor (ST and DT test conditions) task performance than no practice. In addition, consecutive practice resulted in superior motor task performance (ST and DT test conditions) compared to concurrent practice and is, therefore, recommended when executing DT practice schedules.

Valence-dependent neural correlates of augmented feedback processing in extensive motor sequence learning - Part II: Predictive value of event-related potentials for behavioral adaptation and learning

To examine the neural processing of valence-dependent augmented feedback, 38 students learned a sequential arm movement task with 192 trials in each of five practice sessions. The degree of motor automatization was tested under dual-task-conditions. Electroencephalogram (EEG) was recorded in the first and last practice session. This study is an additional analysis of the data from Margraf et al. [Margraf, L., Krause, D., & Weigelt, M. (this issue). Valence-dependent neural correlates of augmented feedback processing in extensive motor sequence learning - Part I: Practice-related changes of feedback processing.]. While Part I focused on changes in neural feedback processing after extensive motor practice, Part II examines coherences between neural feedback processing and short-term behavioral adaptations, as well as different dimensions of long-term learning (i.e., accuracy, consistency, and automaticity). It was found that more negative amplitudes of the feedback-related-negativity (FRN) after negative feedback were predictive for goal-independent changes of behavior in the early practice phase, whereas more positive amplitudes of the late fronto-central positivity (LFCP) after negative feedback were predictive for goal-directed behavioral adaptations (error reduction), independent from the practice phase. Unexpectedly, more positive amplitudes of the P300 after positive feedback were also predictive for goal-directed behavioral adaptations. Concerning long-term learning and motor automatization, a positive correlation was found for the reduction of dual-task costs (DTC) and LFCP-amplitudes after positive feedback in the early practice.

Structuralist mental representation of dual-action demands: Evidence for compositional coding from dual tasks with low cross-task dimensional overlap

The present study asks how behavioral (dual-action) demands in dual tasks are mentally represented and whether changes in representation might govern practice-related dual-task performance improvements. Three different representation accounts were empirically tested based on the idea that dual-action demands required in a dual-task trial might be represented in different ways. According to a compositional (Structuralist) account, component tasks remain structurally intact when combined with another task. In contrast, a holistic (Gestalt) account posits that dual-action requirements in dual tasks are represented holistically and entirely distinct from its component action requirements. Finally, a contextual change account assumes that a change in context (e.g., from single- to dual-action requirement) generally impedes response retrieval, similar to repeating a response while the task context switches. To address this issue, we analyzed trial-by-trial effects in a single/dual switch paradigm (SDS paradigm, involving a randomized mix of single- and dual-task trials within blocks). Specifically, we analyzed performance in an extensive dual-task training setting (involving training sessions across several days) combining an auditory-vocal task and a visual-manual task. The results indicated that, throughout practice, nearly all relevant comparisons of performance between complete switch trials (e.g., between the two single tasks) and partial repetition trials (e.g., from dual to single task) revealed partial repetition benefits, that is, for both the auditory-vocal and the visual-manual task, and for both single- and dual-task performance analyses. Therefore, dual-action requirements in the present dual-task setting are mentally represented in a compositional, Structuralist fashion, probably due to low between-task dimensional overlap.

Learning of across- and within-task contingencies modulates partial-repetition costs in dual-tasking

Dual-task costs might result from confusions on the task-set level as both tasks are not represented as distinct task-sets, but rather being integrated into a single task-set. This suggests that events in the two tasks are stored and retrieved together as an integrated memory episode. In a series of three experiments, we tested for such integrated task processing and whether it can be modulated by regularities between the stimuli of the two tasks (across-task contingencies) or by sequential regularities within one of the tasks (within-task contingencies). Building on the experimental approach of feature binding in action control, we tested whether the participants in a dual-tasking experiment will show partial-repetition costs: they should be slower when only the stimulus in one of the two tasks is repeated from Trial n - 1 to Trial n than when the stimuli in both tasks repeat. In all three experiments, the participants processed a visual-manual and an auditory-vocal tone-discrimination task which were always presented concurrently. In Experiment 1, we show that retrieval of Trial n - 1 episodes is stable across practice if the stimulus material is drawn randomly. Across-task contingencies (Experiment 2) and sequential regularities within a task (Experiment 3) can compete with n - 1-based retrieval leading to a reduction of partial-repetition costs with practice. Overall the results suggest that participants do not separate the processing of the two tasks, yet, within-task contingencies might reduce integrated task processing.

Manual motor reaction while being absorbed into popular music

In three experiments, we investigated the behavioral consequences of being absorbed into music on performance in a concurrent task. We tested two competing hypotheses: Based on a cognitive load account, captivation of attention by the music and state absorption might slow down reactions in the decisional task. Alternatively, music could induce spontaneous motor activity, and being absorbed in music might result in a more autonomous, flow-driven behavior with quicker motor reactions. Participants performed a simple, visual, two-alternative forced-choice task while listening to popular musical excerpts. Subsequently, they rated their subjective experience using a short questionnaire. We presented music in four tempo categories (between 80 and 140 BPM) to account for a potential effect of tempo and an interaction between tempo and absorption. In Experiment 1, absorption was related to decreased reaction times (RTs) in the visual task. This effect was small, as expected in this setting, but replicable in Experiment 2. There was no effect of the music's tempo on RTs but a tendency of mind wandering to relate to task performance. After slightly changing the study setting in Experiment 3, flow predicted decreased RTs, but absorption alone - as part of the flow construct - did not predict RTs. To sum up, we demonstrated that being absorbed in music can have the behavioral consequence of speeded manual reactions in specific task contexts, and people seem to integrate the music into an active, flow-driven and therefore enhanced performance. However, shown relations depend on task settings, and a systematic study of context is necessary to understand how induced states and their measurement contribute to the findings.

No impact of instructions and feedback on task integration in motor learning

This study examined the effect of instructions and feedback on the integration of two tasks. Task-integration of covarying tasks are thought to help dual-task performance. With complete task integration of covarying dual tasks, a dual task becomes more like a single task and dual-task costs should be reduced as it is no longer conceptualized as a dual task. In the current study we tried to manipulate the extent to which tasks are integrated. We covaried a tracking task with an auditory go/no-go task and tried to manipulate the extent of task-integration by using two different sets of instructions and feedback. A group receiving task-integration promoting instructions and feedback (N = 18) and a group receiving task-separation instructions and feedback (N = 20) trained on a continuous tracking task. The tracking task covaried with the auditory go/no-go reaction time task because high-pitch sounds always occurred 250 ms before turns, which has been demonstrated to foster task integration. The tracking task further contained a repeating segment to investigate implicit learning. Results showed that instructions, feedback, or participants' conceptualization of performing a single task versus a dual task did not significantly affect task integration. However, the covariation manipulation improved performance in both the tracking and the go/no-go task, exceeding performance in non-covarying and single tasks. We concluded that task integration between covarying motor tasks is a robust phenomenon that is not influenced by instructions or feedback.

Structuralist Mental Representation of Dual-action Demands: Mechanisms of Improved Dual-task Performance after Practice in Older Adults

Aim: The present study was designed to investigate how behavioral (dual-action) demands in dual tasks are mentally represented in older adults and how these representations might contribute to the practice-related improvement of dual-task performance. Three different theoretical representation accounts were empirically tested: a structuralist account, a holistic account, and a contextual change account. The first account assumes that component tasks remain structurally intact when combined with another task while the second account assumes that dual-action requirements in dual tasks are represented holistically and entirely distinct from its component (single-action) requirements. The final account assumes that a change in context (e.g., from single to dual requirement) might generally impede response retrieval, similar to repeating a response when the task context switches. Methods: To address this issue of dual-action representations in older adults, we assessed trial-by-trial effects in a single/dual switch paradigm (involving a randomized mix of single- and dual-task trials within blocks). In detail, we re-analyzed a large set of practice data involving seven sessions, in which an auditory-vocal task was combined with a visual-manual task.  Results: At the end of practice, the current results were largely consistent with the structuralist account.  Conclusions: We conclude that dual-action requirements in the present dual-task setting are mentally represented in a predominantly structuralist fashion at the end of practice in older adults. The results are discussed in the context of other theories on practice-related mechanisms of improved dual-task performance in this age group.

Ways to Improve Multitasking: Effects of Predictability after Single- and Dual-Task Training

In this study we investigated the effect of predictability on dual-task performance in two experiments. In the first experiment 33 participants separately practiced a continuous tracking task and an auditory reaction time task. Both tasks had a repeating element that made them predictable; in the tracking task this was a repeating segment, and in the auditory task this was an auditory sequence. In addition, one group obtained explicit knowledge about the repeating sequence in the tracking task while the other group trained implicitly. After training, single- and dual-task performance was tested at a post test and retention test. Results showed that predictability only improved performance in the predictable tasks themselves and dual-task costs disappeared for the tracking task. To see whether the task-specific effect of predictability was the results of task prioritization, or because task representations did not have much chance to interact with each other, we conducted a second experiment. Using the same tasks as in Experiment 1, 39 participants now trained both tasks simultaneously. Results largely mirrored those of the first experiment, demonstrating that freed-up resources due to predictability in one task could not be re-invested to improve in the other task. We conclude that predictability has a positive but task-specific effect on dual-task performance.

Normative Data for a Tablet-Based Dual-Task Assessment in Healthy Older Adults

OBJECTIVE

The objective of this study is to provide normative data for a tablet-based dual-task assessment in older adults without cognitive deficits.

METHOD

In total, 264 participants aged between 60 and 90 years, French and English-speaking, were asked to perform two discrimination tasks, alone and concurrently. The participants had to answer as fast as possible to one or two images appearing in the center of the tablet by pressing to the corresponding buttons. Normative data are provided for reaction time (RT), coefficient of variation, and accuracy. Analyses of variance were performed by trial types (single-pure, single-mixed, dual-mixed), and linear regressions assessed the relationship between performance and sociodemographic characteristics.

RESULTS

The participants were highly educated and a large proportion of them were women (73.9%). The accuracy on the task was very high across all blocks. RT data revealed both a task-set cost and a dual-task cost between the blocks. Age was associated with slower RT and with higher coefficient of variability. Men were significantly slower on dual-mixed trials, but their coefficient of variability was lower on single-pure trials. Education was not associated with performance.

CONCLUSIONS

This study provides normative data for a tablet-based dual-task assessment in older adults without cognitive impairment, which was lacking. All participants completed the task with good accuracy in less than 15 minutes and thus, the task is transferable to clinical and research settings.

Retrieval of a well-established skill is resistant to distraction: Evidence from an implicit probabilistic sequence learning task

The characteristics of acquiring new sequence information under dual-task situations have been extensively studied. A concurrent task has often been found to affect performance. In real life, however, we mostly perform a secondary task when the primary task is already well acquired. The effect of a secondary task on the ability to retrieve well-established sequence representations remains elusive. The present study investigates whether accessing well-acquired probabilistic sequence knowledge is affected by a concurrent task. Participants acquired non-adjacent regularities in an implicit probabilistic sequence learning task. After a 24-hour offline period, participants were tested on the same probabilistic sequence learning task under dual-task or single-task conditions. Here, we show that although the secondary task significantly prolonged the overall reaction times in the primary (sequence learning) task, access to the previously learned probabilistic representations remained intact. Our results highlight the importance of studying the dual-task effect not only in the learning phase but also during memory access to reveal the robustness of the acquired skill.

Influences of Dual-Task Training on Walking and Cognitive Performance of People With Relapsing Remitting Multiple Sclerosis: Randomized Controlled Trial

Objective

We sought to investigate whether there is any additional effect of coupled cognitive and physical rehabilitation compared to exercise training alone on walking and cognitive performance in individuals with relapsing remitting multiple sclerosis (RRMS).

Methods

A randomized controlled trial was conducted from March to November 2015 with 30 individuals with RRMS (aged 20 to 50 years; 21 women, 9 men), who underwent detailed medical and neurologic examination. They were randomly allocated using sealed envelopes to either the study group, who received physical and cognitive rehabilitation (dual-task training), or the control group, who received physical rehabilitation alone. Participants (in both groups) were assessed twice (8 weeks apart), before and after rehabilitation. Assessment tools were the Mini-Mental State Examination (MMSE), the Expanded Disability Status Scale (EDSS), neuropsychological evaluation (using RehaCom), and walking tests.

Results

After training, the control group significantly improved regarding MMSE, attention/concentration test, and 10-meter walking test, whereas the scores of the study group significantly improved in all studied parameters (Expanded Disability Status Scale, MMSE, logical reasoning, and attention/concentration and walking tests). The differential (delta) scores from before to after rehabilitation were significantly higher in the study group for logical reasoning, attention/concentration, and 2-minute walking distance scores.

Conclusions

Coupled physical and cognitive (dual-task) training showed concurrent improvement in cognitive and walking abilities in individuals with RRMS which exceeded that achieved by physical training alone.

Dual-memory retrieval efficiency after practice: effects of strategy manipulations

The study investigated practice effects, instruction manipulations, and the associated cognitive architecture of dual-memory retrieval from a single cue. In two experiments, we tested predictions about the presence of learned parallelism in dual-memory retrieval within the framework of the set-cue bottleneck model. Both experiments included three experimental laboratory sessions and involved computerized assessments of dual-memory retrieval performance with strategy instruction manipulations. In Experiment 1, subjects were assigned to three distinct dual-task practice instruction groups: (1) a neutral instruction group without a specific direction on how to solve the task (i.e., neutral instruction), (2) an instruction to synchronize the responses (i.e., synchronize instruction), and (3) an instruction to use a sequential response style (i.e., immediate instruction). Results indicate that strategy instructions are able to effectively influence dual retrieval during practice. Mainly, the instruction to synchronize responses led to the presence of learned retrieval parallelism. Experiment 2 provided an assessment of the cognitive processing architecture of dual-memory retrieval. The results provide support for the presence of a structural bottleneck that cannot be eliminated by extensive practice and instruction manipulations. Further results are discussed with respect to the set-cue bottleneck model.

Effects of task probability on prioritized processing: Modulating the efficiency of parallel response selection

Four experiments investigated the extent to which a limited pool of resources can be shared between different tasks performed simultaneously when it is efficient to do so. The experiments used a prioritized processing paradigm, in which stimuli for both a primary task and a background task were presented in each trial. If the primary-task stimulus required a response in a trial, participants made only that response. If the primary-task stimulus did not require a response, participants responded to the background task. The main manipulation was the relative probability that a response would be required to the primary versus background task. In some blocks, the majority of trials required responses to the primary task (Experiments 1 and 2: 80%; Experiments 3 and 4: 60%), whereas in other blocks the majority required responses to the background task. Background-task responses were substantially faster in blocks where they were more likely to be required, consistent with the idea that more capacity was allocated to them in these blocks. Backward compatibility effects on primary-task responses and stimulus-onset asynchrony effects on background-task responses provided further evidence of greater capacity allocation to the background task when there was a higher probability of responding to it. The results support the view that two tasks can be processed in parallel, with resources divided between them, when it is efficient to do so.

The Effects of Active Self-correction on Postural Control in Girls with Adolescent Idiopathic Scoliosis: The Role of an Additional Mental Task

Due to balance deficits that accompany adolescent idiopathic scoliosis (AIS), the potential interaction between activities of daily living and active self-correction movements (ASC) on postural control deserves particular attention. Our purpose was to assess the effects of ASC movements with or without a secondary mental task on postural control in twenty-five girls with AIS. It is a quasi-experimental within-subject design with repeated measures ANOVA. They were measured in four 20-s quiet standing trials on a force plate: no task, ASC, Stroop test, and both. Based on the center-of-pressure (COP) recordings, the COP parameters were computed. The ASC alone had no effect on any of the postural sway measures. Stroop test alone decreased COP speed and increased COP entropy. Performing the ASC movements and Stroop test together increased the COP speed and decreased COP entropy as compared to the baseline data. In conclusion, our results indicate that AIS did not interfere with postural control. The effects of the Stroop test accounted for good capacity of subjects with AIS to take advantage of distracting attentional resources from the posture. However, performing both tasks together exhibited some deficits in postural control, which may suggest the need for therapeutic consultation while engaging in more demanding activities.

Electrophysiological examination of response-related interference while dual-tasking: is it motoric or attentional?

The possibility that interference between motor responses contributes to dual-task costs has long been neglected, yet is supported by several recent studies. There are two competing hypotheses regarding this response-related interference. The motor-bottleneck hypothesis asserts that the motor stage of Task 1 triggers a refractory period that delays the motor stage of Task 2. The response-monitoring hypothesis asserts that monitoring of the Task-1 motor response delays the response-selection stage of Task 2. Both hypotheses predict lengthening of Task-2 response time (RT2) when Task 1 requires motor processing relative to when it does not. However, they assume different loci for the response-related bottleneck, and therefore make different predictions regarding (a) the interaction between Task-1 motor requirement and the Task-2 difficulty effect as measured by RT2 and (b) the premotoric durations and motoric durations of Task 2 as measured by lateralized readiness potentials (LRPs). To test these predictions, we conducted two experiments manipulating the Task-1 motor requirement (Go vs. NoGo) and Task-2 response-selection difficulty, as well as the stimulus-onset asynchrony (SOA). Task-1 motor processing significantly lengthened RT2, suggesting response-related interference. Importantly, the Task-1 motor response reduced the Task-2 difficulty effect at the short SOA, indicating postponement of the Task-2 motor stage, consistent with the motor-bottleneck hypothesis. Further consistent with the motor-bottleneck hypothesis, the Task-2 LRP indicated a consistent premotoric duration of Task 2 regardless of Task-1 motor requirement. These results are difficult to reconcile with the response-monitoring hypotheses, which places the response-related bottleneck before the response-selection stage of Task 2. The results also have important implications regarding use of locus-of-slack logic in PRP studies.

Structured Cognitive-Motor Dual Task Training Compared to Single Mobility Training in Persons with Multiple Sclerosis, a Multicenter RCT

The aim was to compare the effectiveness of dual-task training (DTT) compared to single mobility training (SMT) on dual-task walking, mobility and cognition, in persons with Multiple Sclerosis (pwMS). Forty pwMS were randomly assigned to the DTT or SMT groups. The DTT-group performed dual-task exercises using an interactive tablet-based application, while the SMT-group received conventional walking and balance exercises. Both interventions were supervised and identical in weeks (8) and sessions (20). Nine cognitive-motor dual-task conditions were assessed at baseline, after intervention and at 4-weeks follow-up (FU). The dual-task cost (DTC), percentage change of dual-task performance compared to single-task performance, was the primary outcome. Mobility and cognition were secondarily assessed. Mixed model analyses were done with group, time and the interaction between group and time as fixed factors and participants as random factors. Significant time by group interactions were found for the digit-span walk and subtraction walk dual-task conditions, with a reduction in DTC (gait speed) for the DTT maintained at FU. Further, absolute dual-task gait speed during walking over obstacles only improved after the DTT. Significant improvements were found for both groups in various motor and cognitive measures. However, the DTT led to better dual-task walking compared to the SMT.

Dual-Task Obstacle Crossing Training Could Immediately Improve Ability to Control a Complex Motor Task and Cognitive Activity in Chronic Ambulatory Individuals With Spinal Cord Injury

Background: The effectiveness of dual-task training has been reported in individuals with cognitive impairments. To date, there is no clear evidence on the incorporation of dual-task training in ambulatory individuals with spinal cord injury (SCI) who have intact cognitive functions but have various degrees of sensorimotor dysfunction. Objectives: To compare the immediate effects of dual-task obstacle crossing (DTOC) and single-task obstacle crossing (STOC) training on functional and cognitive abilities in chronic ambulatory participants with SCI. Methods: This is a randomized 2 × 2 crossover design with blinded assessors. Twenty-two participants were randomly trained using a 30-minute DTOC and STOC training program with a 2-day washout period. Outcomes, including 10-Meter Walk Tests (single- and dual-task tests), percent of Stroop Color and Word Test task errors, Timed Up and Go Test (TUG), and five times sit-to-stand test, were measured immediately before and after each training program. Results: Participants showed significant improvement in all outcomes following both training programs (p < .05), except percent of Stroop Color and Word Test task errors after STOC training. Obvious differences between the training programs were found for the percent of Stroop task errors and TUG (ps = .014 and .06). Conclusion: Obstacle crossing is a demanding task, thus the obvious improvement was found immediately after both training programs in participants with long post-injury time (approximately 5 years). However, the findings primarily suggest the superior effects of DTOC over STOC on a complex motor task and cognitive activity. A further randomized control trial incorporating a complex dual-task test is needed to strengthen evidence for the benefit of DTOC for these individuals.

Dissociative effects of normative feedback on motor automaticity and motor accuracy in learning an arm movement sequence

Within a pre-post-design, we scrutinized the effects of normative augmented feedback with positive and negative valence on learning motor accuracy, consistency as well as automaticity by means of a dual-task paradigm. Forty-two healthy physical education students were instructed to produce an arm-movement sequence as precisely as possible with regard to three spatial reversal points within a time limit of 1200 ms. Twenty-eight practiced an elbow-extension-flexion-sequence (690 trials) and 14 participants were tested as a control group without feedback practice. Valence of normative feedback was systematically manipulated by means of reference lines in a visual feedback display. The reference lines indicated performance of a putative peer-group either to be superior (negative valence, Normative-Negative-Group) or inferior (positive valence, Normative-Positive-Group) to participants' actual performance. As a result, dual-task costs (n-back error) significantly decreased solely in the Normative-Positive-Group, p = .003, η²_p = .51, but in no other group. Surprisingly, the mean absolute error for the motor task significantly decreased (i.e., precision increased) only in the Normative-Negative-Group with a large effect size, but in none of the other groups. Motor consistency was not significantly affected by the valence of normative feedback. According to the hypotheses of error-provoked attentional control, positive feedback-valence appears to enhance skill automatization, while - unexpectedly - only negative feedback-valence seems to enhance movement precision, which may be explained by effects of feedback valence on the learners aspiration level.

Multiple processing limitations underlie multitasking costs

Human multitasking is typically defined as the practice of performing more than one task at the same time (dual task) or rapidly alternating between multiple tasks (task switching). The majority of research in multitasking has been focusing on individual paradigms, with surprisingly little effort in understanding their relationships. We adopted an individual-difference approach to reveal the limitations underlying multitasking costs measured in different paradigms. Exploratory factor analyses revealed not a general multitasking factor but instead three different processing limitations associated with response selection, retrieval and maintenance of task information, and task-set reconfiguration. The three factors were only weakly correlated with and thus not reducible to common measures of processing speed, working memory capacity and fluid intelligence. Males and females excelled in different aspects of multitasking, demonstrating the benefit of using a multifaceted view of multitasking competency in group comparison. Findings of the current study help resolve conflicting results between studies using different paradigms, and form the basis of more comprehensive measurement tools and training protocols covering different aspects of multitasking limitations. The study will also help future integration of multitasking abilities into the theoretical framework of executive function.

Shared or Distinct Attentional Resources? Confounds in Dual Task Designs, Countermeasures, and Guidelines

Human information processing is limited by attentional resources. That is, via attentional mechanisms humans select information that is relevant for their goals, and discard other information. While limitations of attentional processing have been investigated extensively in each sensory modality, there is debate as to whether sensory modalities access shared resources, or if instead distinct resources are dedicated to individual sensory modalities. Research addressing this question has used dual task designs, with two tasks performed either in a single sensory modality or in two separate modalities. The rationale is that, if two tasks performed in separate sensory modalities interfere less or not at all compared to two tasks performed in the same sensory modality, then attentional resources are distinct across the sensory modalities. If task interference is equal regardless of whether tasks are performed in separate sensory modalities or the same sensory modality, then attentional resources are shared across the sensory modalities. Due to their complexity, dual task designs face many methodological difficulties. In the present review, we discuss potential confounds and countermeasures. In particular, we discuss 1) compound interference measures to circumvent problems with participants dividing attention unequally across tasks, 2) staircase procedures to match difficulty levels of tasks and counteracting problems with interpreting results, 3) choosing tasks that continuously engage participants to minimize issues arising from task switching, and 4) reducing motor demands to avoid sources of task interference, which are independent of the involved sensory modalities.