Movement preparation improves touch perception without awareness.
van Ede F., van Doren TI., Damhuis J., de Lange FP., Maris E.
Movements are often directed at external objects, such as when reaching out for a glass to drink from. Surprisingly, however, it is largely unknown how movement plans influence the identification of such external somatosensory stimuli. To address this, we cued participants to prepare for a speeded button press with their left/right thumb and presented a spatially-patterned somatosensory stimulus at either the same or the opposite thumb with equal probability. In contrast to many previous investigations that focused on self-produced somatosensory input and reported attenuated perception, we show that the identification of external stimuli (touch perception) is facilitated by movement preparation. In line with analogous studies in vision, this suggests that movement preparation automatically allocates processing resources (attention) to the location and/or body part of the planned movement. We further show that, in contrast to deliberate somatosensory preparation, participants do not become more confident in their touch perception following movement preparation. These data suggest that the perceptual improvement during movement preparation occurs outside of awareness. Such an unconscious facilitatory process will ensure that relevant parts of the environment are processed with high fidelity, while sparing conscious resources for monitoring other processes in the course of action.