Fig. 1.

Experimental setup and exemplary trials. A: experimental setup. Participants made cued, unconstrained reaches to 5 targets, placed 15-cm high, 20-cm away from the starting position. Between each trial and without the participant's knowledge, the hand weight is modulated by changing a water load attached underneath of the hand. Behind the participant, the experimenter can change the volume of water and thus weight at the participant's hand using a syringe. LED, light-emitting diode. B: a top-down view of movement trajectories. Heavy-to-light (H2L) and light-to-heavy (L2H) trials are plotted for a typical participant in experiment 1. The shaded area denotes ± 1 SD across trials (same below). Positive X displacement stands for moving rightward and positive Y displacement for moving frontward. C: trajectory height as a function of distance from the starting position for the same participant in experiment 1 reaching for the 90° target with 0° angular separation between trials. Positive Z displacement stands for moving upward. H2H, heavy to heavy; L2L, light to light.