Pupillary spectra for use in optical electroencephalography

Pupillary oscillations can correlate with brain activity as measured using electroencephalography (EEG), particularly in the region of the frontal lobe of the brain. Based on this approach, a non-contact EEG has been developed in our lab, offering the advantages that come with remote measuring, such as ease-of-use and flexibility. However, the frequency spectra resulting from the Fourier transform of pupil-size time-series data are in need of pre-processing, in order to show useful signal data. In this contribution, we discuss different pre-processing methods, and show best practices when using this novel approach of working with pupillary spectra. We deal with artefacts and noise; and demonstrate, using data from the ongoing work with our optical EEG setup, the improvements that can be made, recovering a synthetical sine of only 0.04 px² amplitude, invisible in the unfiltered data.