Fig. (6) Two samples of autocorrelation for lengths of EEG segments obtained from occipital (O1) and frontal (F4) cortical areas during 20 min of EEG recording (1 subject). Y-axis, Autocorrelation coefficients; X-axis, Time shift/lag (1, 2, 3, ...). Horizontal doted lines indicate the 95% confidence level. Figure is modified from Fingelkurts et al., 2007, Human Brain Mapping©.