Fig. 3
Aperiodic 1/f slope as a measure of tonic state. (a) Diagram of synchronized pupil and cortical activity. (b) Average spectra and slope estimate per electrode, colored by subject. The aperiodic 1/f estimate is calculated by identifying the slope of a linear fit to a constrained range (20–45 Hz) of the log-log transformed power spectrum. (c) Predicted tonic pupil-to-slope arousal state relationship. At low levels of arousal state, pupil diameter is small and cortical membrane potentials exhibit a large proportion of low-frequency activity and a low proportion of high-frequency activity, which would be reflected as a steeper (more negative) aperiodic slope estimate. At high levels of arousal, pupil diameter is large and cortical membrane potentials exhibit a large proportion of high-frequency activity and a low proportion of low-frequency activity, which would present as a flatter (more positive) slope estimate.
