Locomotor-Cognitive Dual-Tasking in Children with and without Developmental Coordination Disorder

Aetiological accounts recognise the impairment in predictive motor control and cognitive control, as evident in children with Developmental Coordination Disorder (DCD). Given that DCD is defined by a deficit in the development of motor skills, the broad aim of this thesis was to investigate the current underlying explanations for compromised predictive motor control and cognitive control in DCD and its implications for dual-tasking using a hybrid approach.

Cognitive control, synonymous with executive functioning, includes a complex set of neurocognitive and self-regulatory processes, which include attention, and inhibitory control, cognitive flexibility, working memory, and processing speed. These abilities are divided into shifting, updating, and inhibiting components which accumulate into the ability to plan, reason and problem-solve goal-directed actions. Researchers theorise the intertwined nature of cognitive control and predictive motor control as they are both developed in early life and work to reach a mutual goal of action control. Predictive motor control encompasses the ability to estimate the dynamics of limb trajectory, anticipate consequences, rapidly control movements in real-time and internally model behaviour. The capacity to predictively control movements may have a neural underpinning and exists as one of the core deficits of DCD. This predictive control deficit creates various challenges for children with DCD when confronting novel tasks, especially those that require the ability to complete two tasks at once. Dual-tasking is vital for human behaviour and involves the parallel performance of two tasks with distinct goals, the outcome of which can be measured separately. Dual-task performance is typically assessed by the concurrent performance of a motor and cognitive task (e.g., walking by responding to an auditory stimulus). For a child to successfully dual-task they require an ability to share cognitive resources between tasks, enlist control of cognitive functions, prioritise tasks, and automatise motor skills to maintain safety. Therefore, dual-task paradigms are a valuable method of assessing the integration of motor and cognitive control in real time. In light of known deficits, the experimental assessment of dual-task performance was predicted to reveal dual-task performance impairments for children with DCD compared to their typically developing (TD) peers.
 

Study 1 comprises a systematic review and meta-analysis of literature on the latest behavioural and neuroimaging research to clarify the underlying mechanisms and neurocognitive basis of DCD (Chapter 2). This review established fundamental deficits for those with DCD in areas of integration, including visual-motor and cognitive-motor integration. The interpretations of these results highlight that those with DCD may aim to reduce uncertainty by visually guiding each phase of the movement with shorter gaze targets and more frequent fixations than their typical peers. Greater dual-task costs for those with DCD compared to TD peers were also found across locomotor and manual tasks. Patterns of dual-task performance were understood to demonstrate evidence of poor motor skill automatization and, thus, an energy-intensive approach to motor planning and control, which reduced the capacity to share cognitive resources towards an additional task. The reduced automatization, paired with pervasive deficits in cognitive control, particularly during tasks that demand an efficient response or response inhibition is predicted to underlie these areas of difficulty across visual-motor and cognitive-motor integration. Consistent with prior research, individuals with DCD exhibited increased motor variability compared to their TD peers, as evidenced by cautious walking patterns and slower manual control movements. Greater motor variability for individuals with DCD was discussed in light of adaptive benefits (reduced risk of injury) and implications for safety under specific conditions, such as road crossing. Continued areas of exploration were highlighted for cognitive-motor integration as a potential area of impairment in DCD. Thus, this meta-analytical review demonstrated the need for a well-developed dual-task paradigm to explore the underlying areas of potential deficit in DCD.

Study 2 examined locomotor-cognitive dual-task performance in children with and without DCD (6-12 years) (Chapter 6). The participants were required to walk along a straight 12m path and completed a cognitive visual discrimination task at two levels of complexity under single and dual-task conditions. As this study was exploratory, various cognitive and motor metrics were included to explore performance differences. Standard evaluation of dual-task interference (proportional dual-task cost - pDTC) showed that TD children spent a greater proportion of time in double support while dual-tasking. In contrast, children with DCD walked faster when dual-tasking. Within-trial comparison of gait (using proportional within-trial costs - p-WTC) showed that both the TD and DCD groups walked slower before presentation of the cognitive task compared to after the task. Children with DCD showed this pattern for simple and complex cognitive stimuli, whereas for the TD group, it was only confined to the simple condition. Across both typically developing and children with DCD, a potential expectancy effect was observed in relation to the impending cognitive task. The findings of this study were interpreted to reflect the specific task factors, methodology of the chosen dual-task paradigm and participant sample of developing children. Of particular clinical relevance, this research demonstrates how children with DCD can successfully dual-task similarly to their TD peers when their visual systems are not constrained. This study highlighted the need to consider forward modelling (predictive motor control), a known area of deficit in DCD within a dual-task paradigm, to probe the limits of performance in children with DCD.
Study 3 (Chapter 7) extended on the findings of Study 2 by examining locomotor-cognitive obstacle negotiation using an augmented reality dual-task paradigm. The same participants were included in both Study 2 and Study 3. During the Study 3 paradigm, the participants were required to walk along a straight 12m path, step over an obstacle (low and high) at the mid-point while completing the cognitive visual discrimination task (simple and complex), and then walk to the end of the pathway. The findings of this study demonstrated a similar pattern to Study 2, with greater costs on the motor rather than the cognitive outcomes across groups and task combinations. Performance costs are seen across cognitive and gait metrics with the most substantial costs observed at the point of obstacle step-over, seen by leading leg clearance. At the obstacle step-over phase, the DCD group in particular, were observed to negotiate over the obstacle with consistently larger clearance margins and adopted this pattern before their TD peers. The findings of this study established that a complex motor task (obstacle negotiation) appears to be an underlying challenge for children with DCD and that both groups were similarly impaired by the challenging cognitive task while negotiating an obstacle. Future research is suggested to consider task conditions such as challenging terrain or precise stepping and measure vision and visual tracking to examine potential area of difficulty for children with DCD. By assessing dual-task performance under conditions that involve reduced opportunities for motor planning, greater difficulties may be observed for children with DCD.
 

In sum, the overall findings have supported the aims of this thesis by reviewing the current mechanism-focused research in DCD and assessing the implications for cognitive-motor interference. A hybrid approach to dual-task performance was adopted to improve the rigour and relevance of tasks to a population of children with DCD. The novelty of the dual-task paradigm was seen in the use of an augmented-reality headset to present a newly created discrete cognitive paradigm. Both single, dual, proportional dual-task costs and proportional within-task costs were assessed across various task metrics to provide an exploratory overview of how dual-task performance may differ for children with DCD. Thus, the findings of the two experimental studies have progressed the specificity and relevance of dual-task designs and improved our knowledge of differences in DCD. When children completed dual-task paradigms, those with DCD performed similarly to their typical peers when pairing involved the relatively simple motor task of locomotion. As the motor task demands efficient predictive motor control (high obstacle negotiation), dual-task performance costs on obstacle clearance metrics were greater for the DCD group. Whilst inconsistent group differences were found, the innovative dual-task paradigm demonstrates an effect of cognitive task demands that is observable at discrete points of the motor task. The findings of this body of work highlight that those with DCD are able to perform similarly to typically developing children under simple motor task demands, and during increasingly challenging obstacle negotiation demands, they may adaptively compensate for their known difficulties in predictive motor control. In sum, future research is recommended to explore dual-task paradigms with increasingly complex motor task conditions that also consider visuomotor integration for children with DCD. With this knowledge, we can inform the continued evolution of theory, assessment and clinical intervention.

This work © 2024, Emily Subara-Zukic, is licensed under Creative Commons Attribution 4.0 International.