Predictive mechanisms control grip force after impact in self-triggered perturbations.

Impulsive loadings during object grasping are common in everyday life. In predictable conditions, the grip force (GF) increases before the impact to anticipate the perturbation and reaches a maximum after the perturbation. In the present study, the authors addressed the predictive or reactive nature of this late GF component. The load of a handheld object was briskly increased by dropping a mass attached to the object (impact trials). The drop was self-induced, but for one third of the trials, the mechanism was blocked and no impact occurred (blank trials). Evidence that the late GF component is programmed as a predictive action emerged from a systematic comparison between impact and blank trials. The authors conclude that the GF increase occurring after a predictable impulsive loading is essentially of a predictive nature.