Figure 4. RMSE of the systems for the heart-rate task. (a) shows differences in RMSE between the feedback variants for the heart-rate task on an absolute level, (b) shows differences in RMSE of the systems for the heart-rate task on an individual level while (c) shows the number of times a variant was sorted into the respective category. *** significant difference (p < 0.001), ** significant difference (p < 0.01)