Evidence for subjective values guiding cognitive integration of gravity in a free speed manifold pointing task

Studies of regularities in human movement control have led to the idea that our brains incorporate generic motor laws that guide our behaviors and thus these regularities. Among these, it has been argued that a generic internal model of gravity minimizes the bodys energy expenditure during actions performed in the vertical plane. According to this hypothesis, the energy criterion would represent the factor dominating motor planning. However, a growing body of experimental evidence indicates the presence of significant individual sensorimotor differences that suggest the use of various motor decision criteria. We asked 41 voluntary participants to perform a free speed manifold pointing task (i.e., at three free different speeds and toward non-salient targets), in the vertical plane designed to avoid situation-specific responses and favor the expression of singularities. We found that temporal parameters (duration of motion and vigor) were idiosyncratic and not affected by mechanical effects induced by changes in velocity and gravitational force (i.e., assistive or resistive forces). Upward motions had a shorter time to reach maximum velocity than downward motions confirming the presence of asymmetric movement timing. Finally, synchronization of up-down movements was not correlated with energy minimization, indicating that movements performed in the vertical plane do not rely exclusively on a standard representation of gravity reducing effort. Rather, we concluded that individual values and the subjective rewards associated with each of these values could influence the planning of movements executed along the vertical plane as well as the cognitive integration of the gravitational force field.