Are two senses better than (n)one? A systematic review showing advantages of multisensory stimulation for motor learning outcomes.

Multisensory, or multimodal, stimulation refers to the involvement of two or more senses in the guidance of movement. It has been theorized to be more advantageous for motor learning than unimodal, or no sensory stimulation. However, most empirical and applied reviews have used comparisons that often conflate these conditions, making the specific contribution of multimodality difficult to assess. Moreover, previous reviews have only focused on predefined combinations of sensory modalities, or specific types of movement interventions. The present systematic review aimed to provide a more comprehensive synthesis by directly comparing multisensory stimulation against unisensory or no sensory stimulation for motor learning outcomes, across sensory modalities, paradigms and interventions. This review focused on human adult healthy and neurological populations. From 4133 unique records, 39 studies were included in the final synthesis. Results revealed that multisensory stimulation improved motor learning across types of measurements and movements. This was evident for gross motor, and—to a lesser extent—fine motor functions. The latter showed most instances of deterioration, specifically for accuracy-based measures and writing-like movements. However, most instances of deterioration could be explained by withdrawal of the sensory stimulation at testing. Future research should seek to form consensus on a unified definition of what constitutes multisensory stimulation, and the use of unified outcome measures across studies to allow for a quantitative synthesis. Despite these limitations, overall multisensory stimulation shows an advantage over unimodal, and no sensory, stimulation for most motor learning outcomes.