title: The art of braking: Post saccadic oscillations in the eye tracker signal decrease with increasing saccade size.
abstract: Recent research has shown that the pupil signal from video-based eye trackers contains post saccadic oscillations (PSOs). These reflect pupil motion relative to the limbus (Nyström, Hooge, & Holmqvist, 2013). More knowledge about video-based eye tracker signals is essential to allow comparison between the findings obtained from modern systems, and those of older eye tracking technologies (e.g. coils and measurement of the Dual Purkinje Image-DPI). We investigated PSOs in horizontal and vertical saccades of different sizes with two high quality video eye trackers. PSOs were very similar within observers, but not between observers. PSO amplitude decreased with increasing saccade size, and this effect was even stronger in vertical saccades; PSOs were almost absent in large vertical saccades. Based on this observation we conclude that the occurrence of PSOs is related to deceleration at the end of a saccade. That PSOs are saccade size dependent and idiosyncratic is a problem for algorithmic determination of saccade endings. Careful description of the eye tracker, its signal, and the procedure used to extract saccades is required to enable researchers to compare data from different eye trackers.
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: Humanities Laboratory, Lund University, Helgonabacken 12, 22362 Lund, Sweden.
authors.forename: Marcus
authors.initials: M
authors.lastname: Nyström
authors.affiliation: Experimental Psychology, Helmholtz Institute, Utrecht University, Heidelberglaan 1, 3584 CS Utrecht, The Netherlands.
authors.forename: Tim
authors.initials: T
authors.lastname: Cornelissen
authors.affiliation: Humanities Laboratory, Lund University, Helgonabacken 12, 22362 Lund, Sweden.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Holmqvist
mesh_terms: D000328:Adult; D053483:Eye Movement Measurements; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011680:Pupil / Q000502:physiology*; D012438:Saccades / Q000502:physiology*; D015348:Vision, Binocular / Q000502:physiology
keywords: Eye tracking; Post-saccadic oscillation; Saccade