Head movement compensation and multi-modal event detection in eye-tracking data for unconstrained head movements.
The complexity of analyzing eye-tracking signals increases as eye-trackers become more mobile. The signals from a mobile eye-tracker are recorded in relation to the head coordinate system and when the head and body move, the recorded eye-tracking signal is influenced by these movements, which render the subsequent event detection difficult.



The purpose of the present paper is to develop a method that performs robust event detection in signals recorded using a mobile eye-tracker. The proposed method performs compensation of head movements recorded using an inertial measurement unit and employs a multi-modal event detection algorithm. The event detection algorithm is based on the head compensated eye-tracking signal combined with information about detected objects extracted from the scene camera of the mobile eye-tracker.



The method is evaluated when participants are seated 2.6m in front of a big screen, and is therefore only valid for distant targets. The proposed method for head compensation decreases the standard deviation during intervals of fixations from 8° to 3.3° for eye-tracking signals recorded during large head movements.



The multi-modal event detection algorithm outperforms both an existing algorithm (I-VDT) and the built-in-algorithm of the mobile eye-tracker with an average balanced accuracy, calculated over all types of eye movements, of 0.90, compared to 0.85 and 0.75, respectively for the compared algorithms.



The proposed event detector that combines head movement compensation and information regarding detected objects in the scene video enables for improved classification of events in mobile eye-tracking data.
Department of Biomedical Engineering, Lund University, Lund, Box 118, 221 00 Lund, Sweden. Electronic address: linnea.larsson@bme.lth.se.
Linnéa
L
Larsson
Department of Biomedical Engineering, Lund University, Lund, Box 118, 221 00 Lund, Sweden.
Andrea
A
Schwaller
Lund University Humanities Laboratory, Lund, Helgonabacken 12, 223 62 Lund, Sweden.
Marcus
M
Nyström
Department of Biomedical Engineering, Lund University, Lund, Box 118, 221 00 Lund, Sweden.
Martin
M
Stridh
D000328:Adult; D000465:Algorithms; D053483:Eye Movement Measurements; D005133:Eye Movements / Q000502:physiology*; D025461:Feedback, Physiological; D005260:Female; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D008297:Male; D011597:Psychomotor Performance; D012815:Signal Processing, Computer-Assisted; D014796:Visual Perception / Q000502:physiology
Head-tracking; IMU; Mobile eye-tracking; Signal processing; Smooth pursuit