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Licensed Unlicensed Requires Authentication Published by Oldenbourg Wissenschaftsverlag July 16, 2021

Sub-micron pupillometry for optical EEG measurements

Sub-Mikrometer Pupillometrie für optische EEG-Messungen
Niels-Ole Rohweder, Jan Gertheiss and Christian Rembe
From the journal tm - Technisches Messen

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.

Zusammenfassung

Aktuelle Forschungsergebnisse deuten auf eine direkte Korrelation zwischen Gehirnaktivität und Pupillenoszillationen hin. Eine Veröffentlichung von Park und Whang untersucht Schwingungen im Frequenzbereich unter 1 Hz; eine ähnliche Korrelation bei Frequenzen zwischen 1 und 40 Hz ist noch ungeklärt. Zum Nachweis dieser Oszillationen wird jedoch ein Pupillometer mit einer Auflösung von 1 µm benötigt, was die Spezifikationen bestehender Systeme überschreitet. In diesem Beitrag präsentieren wir einen Aufbau, welcher mit einer solchen Auflösung messen kann. Wir betrachten mögliche Rauschquellen, und identifizieren das Quantisierungsrauschen, welches aufgrund der endlichen Pixelgröße der Kamera entsteht, als den fundamentalen Rauschbeitrag. Wir präsentieren ein theoretisches Modell, um das Quantisierungsrauschen der Kamera zu beschreiben, und zeigen, dass unser Algorithmus zur Bestimmung des Pupillendurchmessers eine Subpixel-Auflösung von ca. einem halben Bildpixel oder 12 µm erzielt. Für die Zeitreihen der Durchmesser betrachten wir den Verarbeitungsgewinn durch die Transformation in den Frequenzraum. Damit zeigen wir schließlich, wie eine sub-Mikrometer Auflösung bei der Messung von Pupillenoszillationen erreicht werden kann, und etablierte Pupillometriesysteme übertroffen werden. Dieser Aufbau könnte es ermöglichen, einen funktionsfähigen optischen, vollständig drahtlosen Elektroenzephalograph (EEG) zu entwickeln. Ein solches Gerät könnte ein wertvoller Sensor in vielen Bereichen KI-gestützter Mensch-Maschine-Interaktion sein.

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Received: 2021-02-19
Accepted: 2021-06-29
Published Online: 2021-07-16
Published in Print: 2021-08-27

© 2021 Walter de Gruyter GmbH, Berlin/Boston

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