From lips to hand: How images of lip postures can facilitate hand movements


Humans often perform concurrent mouth and hand movements during physical activity (e.g., contracting orofacial features during a power lift). Indeed, a recent study has shown that the orbicularis oris, a lip muscle involved in lip puckering, shows increased activity during various hand gestures (Higginbotham et al., 2008). Given the bidirectional nature of the relationship between hand and mouth movements (e.g., Gentilucci et al., 2001), it is unclear if the observation of various lip / mouth postures can also facilitate hand movements (i.e., decrease reaction time (RT) relative to baseline). Twenty participants were exposed to images of lip and mouth postures, including lip puckered (kiss) or pressed (smile) or mouth open or closed. In the experimental condition, these images were randomly presented, followed by a fixation cross (green or blue) that prompted participants to perform either a precision or power grip. A control condition involved images devoid of orofacial features. Results indicated a significant decrease in power grip RTs with the "lip puckering" image, relative to its control image. In contrast, no significant reduction in hand grip RTs were found for the other lip/ mouth postures. These findings provide evidence that some lip postures can facilitate the initiation of a hand grip, which further demonstrate the tight coupling between these two effectors.