Figure 1. Experimental design.

(A) example of a trial flow (left to right) during a learning epoch under “L-rate” and “H-rate” practice schedules. During the first delay period the monkey held the robotic arm in the center without moving it. The monkey kept holding at the central circle after target onset for an additional delay and moved after the go signal. In the figure the learned target is at 0° and the force field (FF) is clockwise (parallel arrows). If the lit target was the selected learned target (lower row), then the force-field was applied when movement was initiated, otherwise (upper row) movement was executed under standard conditions. Under the L-rate schedule the learned target appeared as often as the other targets (N), and under the H-rate schedule, four times more frequently (4*N). (B) Recording day flow: all days started with standard trials (center-out reaching movements to eight directions) followed by a learning epoch. From the first day until the day before last (fourth day under the L-rate, first day under the H-rate) the learning epoch was followed by a second standard epoch and then ended with a second learning epoch. The last day of the learning set (fifth day under the L-rate, second day under the H-rate) consisted of only three epochs in which learning was followed by a long standard epoch (“washout”).