title: The pupil is faster than the corneal reflection (CR): Are video based pupil-CR eye trackers suitable for studying detailed dynamics of eye movements?
abstract: Most modern video eye trackers use the p-CR (pupil minus CR) technique to deal with small relative movements between the eye tracker camera and the eye. We question whether the p-CR technique is appropriate to investigate saccade dynamics. In two experiments we investigated the dynamics of pupil, CR and gaze signals obtained from a standard SMI Hi-Speed eye tracker. We found many differences between the pupil and the CR signals. Differences concern timing of the saccade onset, saccade peak velocity and post-saccadic oscillation (PSO). We also obtained that pupil peak velocities were higher than CR peak velocities. Saccades in the eye trackers' gaze signal (that is constructed from p-CR) appear to be excessive versions of saccades in the pupil signal. We conclude that the pupil-CR technique is not suitable for studying detailed dynamics of eye movements.
authors.affiliation: Experimental Psychology, Helmholtz Institute, Utrecht University, Heidelberglaan 1, 3584 CS Utrecht, The Netherlands. Electronic address: i.hooge@uu.nl.
authors.forename: Ignace
authors.initials: I
authors.lastname: Hooge
authors.affiliation: Lund University Humanities Lab, Lund University, Helgonabacken 12, 22362 Lund, Sweden; School of Languages and Academic Literacy, Vaal Triangle Campus, North-West University, Vanderbijlpark 1900, South Africa.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Holmqvist
authors.affiliation: Lund University Humanities Lab, Lund University, Helgonabacken 12, 22362 Lund, Sweden.
authors.forename: Marcus
authors.initials: M
authors.lastname: Nyström
mesh_terms: D000328:Adult; D003315:Cornea; D053483:Eye Movement Measurements / Q000592:standards; D005133:Eye Movements; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D011680:Pupil / Q000502:physiology*; D012438:Saccades / Q000502:physiology*; D015348:Vision, Binocular / Q000502:physiology
keywords: Corneal reflection; Pupil; Saccades