Sub-micron pupillometry for optical EEG measurements

Abstract

Recent research indicates that a direct correlation exists between brain activity and oscillations of the pupil. A publication by Park and Whang shows measurements of excitations in the frequency range below 1 Hz. A similar correlation for frequencies between 1 Hz and 40 Hz has not yet been clarified. In order to evaluate small oscillations, a pupillometer with a spatial resolution of 1 µm is required, exceeding the specifications of existing systems. In this paper, we present a setup able to measure with such a resolution. We consider noise sources, and identify the quantisation noise due to finite pixel sizes as the fundamental noise source. We present a model to describe the quantisation noise, and show that our algorithm to measure the pupil diameter achieves a sub-pixel resolution of about half a pixel of the image or 12 µm. We further consider the processing gains from transforming the diameter time series into frequency space, and subsequently show that we can achieve a sub-micron resolution when measuring pupil oscillations, surpassing established pupillometry systems. This setup could allow for the development of a functional optical, fully-remote electroencephalograph (EEG). Such a device could be a valuable sensor in many areas of AI-based human-machine-interaction.