Fig. 4.

Normalised EEG spectra under different light intensities. Spectral heatmaps show normalised and group-averaged EEG time–frequency spectra from object recognition trials under 5 lx (left panel), 50 lx (middle panel), and 500 lx (right panel). EEG spectra (in μV² per 0.25 Hz) during sample and test phases were normalised to the EEG spectrum (in μV² per 0.25 Hz) in the corresponding frequency bins during the baseline period. Fast θ (8.5–11.2 Hz) and slow γ frequency bands (35–50 Hz) are indicated in each panel. The warmer the colour (red) is on the heatmap, the greater is the increase in EEG power at a particular frequency relative to baseline; whereas darker colours (blue) indicate that there is minimal change or a decrease in EEG power at a particular frequency relative to baseline.