The Influence of Mirror-Visual Feedback on Training-Induced Motor Performance Gains in the Untrained Hand

Abstract

The well-documented observation of bilateral performance gains following unilateral motor training, a phenomenon known as cross-limb transfer, has important implications for rehabilitation. It has recently been shown that provision of a mirror image of the active hand during unilateral motor training has the capacity to enhance the efficacy of this phenomenon when compared to training without augmented visual feedback (i.e., watching the passive hand), possibly via action observation effects [1]. The current experiment was designed to confirm whether mirror-visual feedback (MVF) during motor training can indeed elicit greater performance gains in the untrained hand compared to more standard visual feedback (i.e., watching the active hand). Furthermore, discussing the mechanisms underlying any such MVF-induced behavioural effects, we suggest that action observation and the cross-activation hypothesis may both play important roles in eliciting cross-limb transfer. Eighty participants practiced a fast-as-possible two-ball rotation task with their dominant hand. During training, three different groups were provided with concurrent visual feedback of the active hand, inactive hand or a mirror image of the active hand with a fourth control group receiving no training. Pre- and post-training performance was measured in both hands. MVF did not increase the extent of training-induced performance changes in the untrained hand following unilateral training above and beyond those observed for other types of feedback. The data are consistent with the notion that cross-limb transfer, when combined with MVF, is mediated by cross-activation with action observation playing a less unique role than previously suggested. Further research is needed to replicate the current and previous studies to determine the clinical relevance and potential benefits of MVF for cases that, due to the severity of impairment, rely on unilateral training programmes of the unaffected limb to drive changes in the contralateral affected limb.

Effects of mirror training on motor performance in healthy individuals: a systematic review and meta-analysis

“…Nine studies were conducted in Germany18–26 (including one in collaboration with China) 19. Two studies were conducted in Australia,27 28 and the other three studies were performed in Japan,29 the Netherlands30 and the USA 31. The studies were categorised according to their duration of experimental training.…”

“…The studies were categorised according to their duration of experimental training. Five studies involved long-term tasks (more than 1 day, continuous training),23–26 30 while the other nine studies adopted short-term training within 1 day to evaluate immediate functional effects 18–22 27–29 31…”

“…The studies mainly focused on the effects of MTr on the motor functional improvements of healthy individuals following various training schemes. Eleven studies compared MTr with different training patterns: an active vision pattern, in which the participants only saw their moving limb; a passive vision pattern, in which the participants saw their inactive limb through glass rather than their active limb; and an action observation pattern, in which the participants saw the movements conducted by others without moving their own bilateral limb 18 19 21 22 27–29 31. The other three studies investigated the effects of independent variables (ie, age, skill level and hand dominance) on motor performance in healthy individuals 18 26 28.…”

“…Eight studies examined the functional performance of the untrained hand using MTr with an active vision pattern in which the participants saw their moving hand 19 21–25 27 31. Seven studies showed an unclear risk of bias and one had a low risk of bias.…”

Bilateral transfer phenomenon: A functional magnetic resonance imaging pilot study of healthy subjects

“…1 The possibility of transfer of a motor skill from one hand to the other, performing repetitive movements, is called bilateral transfer (BT) or crosslimb transfer. [2][3][4] The neural mechanism underlying this phenomenon is not fully clear. There are three main models explaining it: the first model is the 'callosal access' which proposes that the motor ability is generated in the dominant hemisphere and then reached by the opposite one through the corpus callosum to facilitate task execution with the untrained limb.…”