Abstract
Exposure to online reach error induced by unseen target jumps can lead to implicit reach adaptation, even if online control reduces the terminal hand-to-target error by the end of the movement (Cameron et al. 2011). We investigated the effects of a terminal effector perturbation that counteracted the online error from a target jump. Participants looked and reached to a target with their unseen hand. A cursor representing hand position was removed during the saccade and restored at movement end for terminal feedback. In the Target condition, the target jumped forward during the saccade, requiring participants to adjust their reach. In the Target-Effector condition, both target and cursor moved, with the change in cursor position resulting in a comparable perturbation size to the target jump. Participants effectively had to reach for the initial target position and not adjust for the jump to get the cursor on target. Participants were not informed of the target or cursor perturbation. We tested whether exposure to the target jumps produced reach aftereffects when reaching to stationary targets, and if perturbed terminal feedback of the reach position affected adaptation. All participants (12) adjusted their reaches when exposed to repeated target jumps to maintain performance. When the terminal feedback cursor was also displaced to counteract the target jump, participants completed their reaches to the original target position. In no-feedback post-tests, unaware participants (9) showed implicit overshoot aftereffects only in the Target condition. Results suggest an interaction between adaptive changes due to online vs. terminal error signals.
