Fig 3. Boxplots of information-theoretic measures P _RR (p < 0.01), T _{RSP → RR} (p > 0.05), S _RR (p > 0.05), C _{RSP → RR} (p > 0.05) and S _RR|RSP (p < 0.0001), estimated using the nonlinear model-free approach, during baseline (BASE), sustained attention (AT) and the mental stress tasks (MT1 and MT2).

The square brackets indicate significant differences between those two mental states as determined by the Friedman test and post hoc contrasts.