Figure 5. Instantaneous tracking of the HRV indices computed from a representative subject using the proposed NARI model during the passive emotional elicitation (two neutral sessions alternated to a L-M and a M-H arousal session).

In the first panel, the estimated μ_RR(t, , ξ(t)) is superimposed on the recorded R-R series. Below, the instantaneous heartbeat power spectra evaluated in Low frequency (LF) and in High frequency (HF), the sympatho-vagal balance (LF/HF), several bispectral statistics such as the nonlinear sympathovagal interactions LL, LH, and HH, and the instantaneous dominant Lyapunov exponent (IDLE) are reported. In the three bottom panels, the tracking of emotion classification is shown in terms of arousal (A), valence (V), and their combination according to the circumplex model of affect (see Fig. 1). In such panels, the correct image classification is marked in red, whereas the misclassification is marked in blue. The neutral sessions are associated to the L-M arousal class exclusively without related valence class. This choice is justified as neutral stimuli could be arbitrarily associated to the L-M or M-H valence.