Figure 4.

Frequency-domain analysis of differences in heart rate variability between the emotions of pleasure, happiness, fear, and anger. In power spectrum density (PSD), frequencies between 0.04 Hz and 0.15 Hz are defined as low frequency (LF) and those between 0.15 Hz and 0.4 Hz are defined as high frequency (HF). Utilizing the differences in the distribution of PSD with frequency changes, we found that the characteristic of the PSD was low for both the HF and LF of fear; high HF and low LF were observed for happiness. Although both pleasure and anger have signal strength in LF and HF parts, the intensity of the HF of pleasure was relatively higher than that of anger; this difference can be used for emotion classification.