Fig. 1: Illustration of group-averaged power spectra from two representative cortical regions F5 (left) and P3 (right) in the HC (upper panels) and SZ (bottom panels) cohorts.

In every panel, gray lines indicate the mixed (i.e., raw), while black lines the isolated fractal power spectra, respectively, with gray shaded areas denoting the standard error of the mean. Inset plots show corresponding isolated oscillatory spectra, obtained by subtracting the fractal from the raw (mixed) spectra. Boundaries of the two frequency regimes of interest (1–4 Hz and 20–45 Hz) are indicated with black dashed lines, while the range excluded from slope estimation (4–20 Hz) is marked in yellow. Blue and red dashed lines are illustrative and depict the power-law functions fitted on the fractal spectra in the low- and high-frequency regimes, respectively, with their corresponding slopes presented in matching colors. The panels illustrate that IRASA is effective in separating the fractal from the mixed power spectrum with minimal residual effect, and the utilized parameter settings and employed frequency regimes allow for unbiased estimates. In both groups low- and high-range slopes are roughly equal over F5 region, while the spectrum appears steeper in high- compared to low-range over P3. HC healthy control, SZ schizophrenia, IRASA irregular resampling auto-spectral analysis.