Tracking Error. Average RMSE over skill practice (days 1 and 2). Open shapes represent performance on the sequence epoch, closed shapes represent the random epoch. Panel (a) displays the performance of the AV group that experienced vibration to the active tracking arm. Panel (b) displays the performance of the CTL group that experienced vibration to the passive, unused arm. Block 1 represents initial performance with attenuating visual feedback but also vibration. The remaining blocks with vibration and minimal visual feedback, show an interaction of epoch and block suggesting improvement on sequence epoch tracking over time. Decreased RMSE, towards graph bottom, denotes performance improvements.