Figure 6

Main effects of task and difficulty level on the variability of displacement during slow waveform tracking. The root mean square error (RMSE) in hand (a, c) and tongue (b, d) in Part 2 of Session 2 are presented. Difficulty levels include square-wave and sine wave. H, independent hand task; T, independent tongue task; HT, concurrent hand-tongue task; HC, concurrent hand-cognitive task; TC, concurrent tongue-cognitive task. **, P < 0.01.