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Tracking the Closed Eye by Calibrating Electrooculography with Pupil-Corneal Reflection

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Tracking the Closed Eye by Calibrating Electrooculography with Pupil-Corneal Reflection TRACKING THE CLOSED EYE BY CALIBRATING ELECTROOCULOGRAPHY WITH PUPIL-CORNEAL REFLECTION by Raymond R. MacNeil B.Sc., University of Toronto, 2016 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Psychology) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) August 2020 © Raymond R. MacNeil, 2020 The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, the thesis entitled: TRACKING THE CLOSED EYE BY CALIBRATING ELECTROOCULOGRAPHY WITH PUPIL-CORNEAL REFLECTION submitted by Raymond R. MacNeil in partial fulfillment of the requirements for the degree of Master of Arts in Psychology Examining Committee: Dr. James T. Enns (Psychology, Faculty of Arts) Supervisor Dr. Ipek Oruc (Ophthalmology and Visual Sciences, Faculty of Medicine) Supervisory Committee Member Dr. Peter Graf (Department of Psychology, Faculty of Arts) Supervisory Committee Member ii Abstract Electrooculography (EOG) offers several advantages over other methods for tracking human eye movements, including its low cost and capability of monitoring gaze position when the eyelids are closed. Yet, EOG poses its own challenges, because in order to determine saccadic distance and direction, the electrical potentials measured by EOG must be calibrated in some way with physical distance. Moreover, the EOG signal is highly susceptible to noise and artifacts arising from a variety of sources (e.g., activity of the extraocular muscles). Here we describe a method for estimating a corrected EOG signal by simultaneously tracking gaze position with an industry standard pupil-corneal reflection (PCR) system. We first compared the two measurements with the eyes open under two conditions of full illumination and in a third condition of complete darkness. Compared to the PCR signal, the EOG signal was less precise and tended to overestimate saccadic amplitude. We harnessed the relation between the two signals in the dark condition in order to estimate a corrected EOG-based metric of saccade end-point amplitude in a fourth condition, where the participants eyes were closed. We propose that these methods and results can be applied to human-machine interfaces that rely on EOG eye tracking, and for advancing research in sleep, visual imagery, and other situations in which participants’ eyes are moving but closed. iii Lay Summary Homo sapiens are insatiable infovores, making eye movements almost constantly to take in new information. Most eye movement research has focused on the activity of the eyes while the eyelids are open. Comparatively little is known about eye movements when the eyelids are closed — as when we dream, meditate, or imagine — because the current tools for doing so are limited. This thesis describes an approach to measuring closed-eye movements that combines an older eye tacking technique with a modern one in order to improve closed-eye tracking accuracy. The results show that this technique holds promise for improved use of closed-eye movements in the of control human-machine interfaces and for research on spatial cognition. iv Preface I, Raymond MacNeil, am the primary author of the work presented within this thesis. I was responsible for writing the manuscript, analyzing the data, and interpreting the results. One section of this thesis describes an algorithm used to process data collected with a pupil-corneal reflection eye tracker. I alone wrote the code and developed the concepts that underpin this algorithm. Dr. James T. Enns was the supervisory author and provided essential feedback and guidance throughout the entire research process. He also made substantial contributions to editing the manuscript throughout its development. The key idea underpinning this work is best attributed to Dr. Enns. Both Dr. Enns and I designed the experiment and worked out the finer details of its implementation. P.D.S.H Gunawardane, who is co-supervised by Drs. Mu Chiao (Microelectromechanical Systems Laboratory) and Clarence W. de Silva (Industrial Automation Laboratory), oversaw the technical aspects of the electrooculography recordings. Jamie Dunkle (Research Technician, UBC Vision Lab) wrote the software for the experiment and provided technical assistance throughout the course of the study. P.D.S.H Gundarwane, Leo Zhao, Jamie Dunkle, and I each contributed to writing the code/algorithms that were used to process the EOG data. Figure 4 was adapted from work performed by Jamie Dunkle. All research that is described here was conducted in adherence to Canada’s Tri-Council Policy Statement: Ethical Conduct for Research Involving Humans (2nd Ed.) and received approval from The University of British Columbia’s behavioural research ethics board (H18- 03792). In the course of my Master’s program I received funding from the Natural Sciences and Engineering Research Council (CGS-M). I also received internal funding from UBC in the form of a Faculty of Arts Graduate Award. v Table of Contents ABSTRACT..................................................................................................................................................iii LAY SUMMARY ......................................................................................................................................... iv PREFACE ..................................................................................................................................................... v TABLE OF CONTENTS ............................................................................................................................. vi LIST OF TABLES ..................................................................................................................................... viii LIST OF FIGURES ..................................................................................................................................... ix ACKNOWLEDGEMENTS .......................................................................................................................... x DEDICATION.............................................................................................................................................. xi INTRODUCTION ......................................................................................................................................... 1 EOG HISTORY AND BACKGROUND .............................................................................................................. 1 OTHER EYE TRACKING SYSTEMS ................................................................................................................. 3 Scleral Search Coil Technique. ............................................................................................................... 3 Infrared-Based Pupil-Corneal Reflection Eye Tracking. ......................................................................... 5 UNIQUE STRENGTHS OF EOG ...................................................................................................................... 6 STUDY OVERVIEW....................................................................................................................................... 7 Research Aim One. ................................................................................................................................. 7 Research Aim Two .................................................................................................................................. 8 Research Aim Three ............................................................................................................................... 9 METHOD .................................................................................................................................................... 11 PARTICIPANTS ........................................................................................................................................... 11 MATERIALS AND APPARATUS .................................................................................................................... 11 PROCEDURE .............................................................................................................................................. 13 vi Preparation. ......................................................................................................................................... 13 EyeLink Setup & Calibration ................................................................................................................ 15 EOG Calibration & Training Protocol ................................................................................................. 16 Task Conditions .................................................................................................................................... 17 EYELINK DATA PREPROCESSING ............................................................................................................... 18 COMPLEX-AND-MULTIEVENT GAZE PATTERN PARSER .............................................................................. 21 EOG DATA PROCESSING ........................................................................................................................... 25 DATA ANALYSIS ....................................................................................................................................... 27 EOG Correction Models ......................................................................................................................
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