title: Pupil size influences the eye-tracker signal during saccades.
abstract: While it is known that scleral search coils-measuring the rotation of the eye globe--and modern, video based eye trackers-tracking the center of the pupil and the corneal reflection (CR)--produce signals with different properties, the mechanisms behind the differences are less investigated. We measure how the size of the pupil affects the eye-tracker signal recorded during saccades with a common pupil-CR eye-tracker. Eye movements were collected from four healthy participants and one person with an aphakic eye while performing self-paced, horizontal saccades at different levels of screen luminance and hence pupil size. Results show that pupil-, and gaze-signals, but not the CR-signal, are affected by the size of the pupil; changes in saccade peak velocities in the gaze signal of more than 30% were found. It is important to be aware of this pupil size dependent change when comparing fine grained oculomotor behavior across participants and conditions.
authors.affiliation: Lund University Humanities Laboratory, Lund, Sweden. Electronic address: marcus.nystrom@humlab.lu.se.
authors.forename: Marcus
authors.initials: M
authors.lastname: Nyström
authors.affiliation: Experimental Psychology, Helmholtz Institute, Utrecht University, Utrecht, The Netherlands. Electronic address: i.hooge@uu.nl.
authors.forename: Ignace
authors.initials: I
authors.lastname: Hooge
authors.affiliation: Department of Philosophy & Cognitive Science, Lund University, Sweden. Electronic address: richard.andersson@humlab.lu.se.
authors.forename: Richard
authors.initials: R
authors.lastname: Andersson
mesh_terms: D000328:Adult; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D008297:Male; D011680:Pupil / Q000502:physiology*; D012438:Saccades / Q000502:physiology*; D055815:Young Adult
keywords: Eye-tracker signal; Pupil size; Saccade shape