Research suggests that motor difficulties in Developmental Coordination Disorder (DCD) are related to altered motor sequence planning, but it is unclear which mechanisms are affected, particularly in adults. This study addresses that gap by examining how the order of upcoming movements during the planning of skilled typing sequences affects motor production in adults with DCD. Previous monkey neurophysiology and behavioural findings in humans have shown that elements of a sequence are pre-ordered prior to execution, known as competitive queuing (CQ). CQ quality is predictive of subsequent performance, with skilled performers, those with fewer errors, having a larger position-dependent difference. DCD (N=28) and control participants (N=54) performed two 4-element finger sequences from memory in a delayed sequence production task over 3 sessions. Probe trials, which involved participants performing a single press after the Go Cue, assessed motor planning at each sequence position by measuring reaction time (RT) and error rate. We found that adults with DCD had a higher error rate and were slower to initiate and perform correct sequences. In terms of planning, the DCD group showed reduced pre-ordering of sequence elements. Whilst the DCD group had a higher error rate on a working memory task, this was not correlated with the degree of pre-ordering of presses of the upcoming sequence. These findings suggest that disrupted motor sequence planning in DCD is characterised specifically by a failure to pre-order movements during the retrieval of sequences from memory. Additionally, motor sequence pre-ordering deficits in DCD are independent of general working memory impairments. These results extend prior evidence from motor imagery paradigms, demonstrating that internal modelling deficits are evident during the execution of motor plans.
Wright-Wieckowski, H., Wilmut, K., Kornysheva, K.
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