title: A novel method for measuring gaze orientation in space in unrestrained head conditions.
abstract: Investigation of eye movement strategies often requires the measurement of gaze orientation without restraining the head. However, most commercial eye-trackers have low tolerance for head movements. Here we present a novel geometry-based method to estimate gaze orientation in space in unrestricted head conditions. The method combines the measurement of eye-in-head orientation-provided by a head-mounted video-based eye-tracker-and head-in-space position and orientation-provided by a motion capture system. The method does not rely on specific assumptions on the configuration of the eye-tracker camera with respect to the eye and uses a central projection to estimate the pupil position from the camera image, thus improving upon previously proposed geometry-based procedures. The geometrical parameters for the mapping between pupil image and gaze orientation are derived with a calibration procedure based on nonlinear constrained optimization. Additionally, the method includes a procedure to correct for possible slippages of the tracker helmet based on a geometrical representation of the pupil-to-gaze mapping. We tested and validated our method on seven subjects in the context of a one-handed catching experiment. We obtained accuracy better than 0.8° and precision better than 0.5° in the measurement of gaze orientation. Our method can be used with any video-based eye-tracking system to investigate eye movement strategies in a broad range of naturalistic experimental scenarios.
authors.affiliation: Laboratory of Neuromotor Physiology, IRCCS Santa Lucia Foundation, Rome, Italy. b.cesqui@hsantalucia.it
authors.forename: Benedetta
authors.initials: B
authors.lastname: Cesqui
authors.forename: Rolf van
authors.initials: Rv
authors.lastname: de Langenberg
authors.forename: Francesco
authors.initials: F
authors.lastname: Lacquaniti
authors.forename: Andrea
authors.initials: A
authors.lastname: d'Avella
mesh_terms: D000328:Adult; D053483:Eye Movement Measurements / Q000295:instrumentation*; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D019416:Head Movements; D006801:Humans; D008297:Male; D009949:Orientation / Q000502:physiology*; D014741:Video Recording; D055815:Young Adult
keywords: calibration; drift correction; gaze orientation in space; nonlinear optimization; oculography