Learning to reach with error amplification post-stroke : the contributions of explicit and implicit adaptation processes

Error augmentation (EA) is a practice technique that uses visual feedback to amplify errors during reaching movements. EA has been used to improve motor skill acquisition in controls and arm motor control post-stroke. However, there is uncertainty about the technique’s effectiveness and underlying learning processes. In this dissertation I tested the efficacy of EA for improving adaptation of a novel visuomotor skill and investigated the learning processes engaged when practicing with EA. Given mixed findings about EA’s effectiveness, an aim was to identify individual difference factors associated with response to EA interventions including age, spatial working memory, and structural differences in brain networks resulting from stroke lesions. I also tested how EA affects motivation, to see if exaggerating errors makes practice feel more challenging and less enjoyable. In Experiments 1 and 2, participants learned to adapt reaches to rotated cursor feedback with and without EA. EA enhanced detection of rotated cursor feedback and promoted explicit strategy use. Despite increasing error awareness, EA did not improve performance or learning for younger or older adults. Meanwhile, EA benefited practice performance but not learning for individuals with stroke. Older adults showed less explicit and overall adaptation to rotated feedback than younger adults (Experiment 1). Compared to older adults, individuals with stroke achieved even less explicit and overall adaptation, with many showing impaired ability to develop an explicit strategy (Experiment 2). Across both experiments, mental rotation abilities were important for explicit adaptation. EA made performance appear worse and negatively impacted perceived competence for all participants, but only younger adults rated practice with EA as less enjoyable than practice without. In Experiment 3, I tested if stroke participants with explicit adaptation impairments could apply a provided strategy. Relative to older adults, a subgroup of stroke participants had impaired adaptation performance when using a strategy, which was associated with lesion-driven structural disconnection in the right pre-central, post-central, and supramarginal gyri. Overall, this dissertation advances our understanding of EA’s effect on adaptation learning processes, how stroke impacts explicit adaptation, and brain regions that may be critical for integrating strategies when adapting reaching movements in novel feedback environments.

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