Fig. 3.

Comparisons of conventional EEG and ear-EEG. It is observed that there are clear spectral similarities between the NREM stages for scalp and ear electrodes, and that the spectral distributions are clearly distinctive from the spectral distributions of the REM stages. However, is also seen that while much of the sleep information is inherited by the ear-EEG, the stage signatures are not completely identical, leading to our use of automatic classifiers. a Spectral power distribution in the three major sleep stages. Normalized to have similar power for top half of spectrum. b Sleep events shown for different electrode pairs, simultaneously recorded. Data has been subjected to a [1; 99] Hz band-pass filter, as well as a 50 Hz notch filter