Figure 2.

Experimental conditions and protocol. As a combination of directional and temporal prior knowledge conditions, four conditions were tested for acceleration and deceleration perturbations (A). For EMG analyses on trials in which the participants knew the timing of an upcoming perturbation (T+), catch trials in which they had been warned but not perturbed were used as reference (written in parenthesis). Each directional prior knowledge condition was tested in separate experimental sessions (B). Before the sessions start, the participants were instructed which perturbation might occur (e.g., the right belt might be accelerated in the session 1). The order of acceleration and deceleration sessions (1 and 2) was counterbalanced among subjects.