Figure 1. Task design.

(A) Reaching task. Participants reach from a start location (white circle) to a target (blue dot). Online feedback is provided by a cursor (white dot). The target is displayed in a fixed location for the entire experiment (location varied across participants). After a random delay, a tone or a light (white frame) is presented, serving as the movement imperative. The participant is instructed to move directly to the target. The cue persists until the radial position of the hand reaches the target distance. The hand is not visible during the reach; instead, feedback is provided only by the cursor. (B) Components and timing of the reaching task described as conditioning events. The tone and light imperatives serve as conditioned stimuli (CSs), and the cursor feedback is the unconditioned stimulus (US). In our experiments, the radial position of the cursor is aligned with the hand, but the angular position is fixed (‘clamped’), appearing either 15° away from the target (resulting in an error signal) when paired with one of the CS’s (CS+) or at the target when paired with the other CS (CS−). After repeated pairings of the CS+ and US, a conditioned response (CR) develops, leading to an adaptive feedforward movement response in a direction opposite to the rotated feedback. Note that we include an unconditioned response (UR) in the schematic, what we assume is an online, automatic corrective response to the visual error. However, because participants are instructed to move fast, the UR is negligible.