Short-term mirror visual feedback training enhances performance gains in the untrained hand for a complex motor sequence learning task

Mirror Visual Feedback (MVF) is an experimental paradigm that simultaneously combines action observation and cross-education, and has been proposed to produce greater performance gains in the untrained limb than either action observation or cross-education alone. Existing studies investigating the effects of unilateral training under MVF on the performance of the untrained limb are limited, and their findings are mixed. In this between-groups study, we investigated the effects of MVF training on untrained left-hand performance in a complex motor sequence learning task involving fine finger movements. Statistically significant performance gains were observed in the untrained left-hand following dominant right-hand training under both normal visual feedback (NVF) and MVF conditions. Critically, the magnitude of performance gains was significantly greater following MVF training than following NVF training, indicating that MVF enhanced untrained-hand performance beyond that associated with cross-education alone. We also investigated the effects of MVF training on the untrained left-hand's performance for novel movement sequences (i.e., movement sequences not practiced by the right-hand during training). Statistically significant performance gains for these novel movement sequences were observed in the untrained left-hand following right-hand training under both NVF and MVF conditions; however, the magnitude of these gains was comparable. Thus, the additional performance benefit associated with MVF in the untrained left-hand for sequences practiced by the right-hand during training did not extend to novel movement sequences. Finally, we highlight several task-design considerations that may inform future studies seeking to enhance MVF-related performance gains in the untrained limb.