title: The influence of crystalline lens accommodation on post-saccadic oscillations in pupil-based eye trackers.
abstract: It is well known that the crystalline lens (henceforth lens) can oscillate (or 'wobble') relative to the eyeball at the end of saccades. Recent research has proposed that such wobbling of the lens is a source of post-saccadic oscillations (PSOs) seen in data recorded by eye trackers that estimate gaze direction from the location of the pupil. Since the size of the lens wobbles increases with accommodative effort, one would predict a similar increase of PSO-amplitude in data recorded with a pupil based eye tracker. In four experiments, we investigated the role of lens accommodation on PSOs in a video-based eye tracker. In Experiment 1, we replicated previous results showing that PSO-amplitudes increase at near viewing distances (large vergence angles), when the lens is highly accommodated. In Experiment 2a, we manipulated the accommodative state of the lens pharmacologically using eye drops at a fixed viewing distance and found, in contrast to Experiment 1, no significant difference in PSO-amplitude related to the accommodative state of the lens. Finally, in Experiment 2b, the effect of vergence angle was investigated by comparing PSO-amplitudes at near and far while maintaining a fixed lens accommodation. Despite the pharmacologically fixed degree of accommodation, PSO-amplitudes were systematically larger in the near condition. In summary, PSOs cannot exhaustively be explained by lens wobbles. Possible confounds related to pupil size and eye-camera angle are investigated in Experiments 3 and 4, and alternative mechanisms behind PSOs are probed in the discussion.
authors.affiliation: Humanities Laboratory, Lund University, Helgonabacken 12, 22362 Lund, Sweden. Electronic address: marcus.nystrom@humlab.lu.se.
authors.forename: Marcus
authors.initials: M
authors.lastname: Nyström
authors.affiliation: Humanities Laboratory, Lund University, Helgonabacken 12, 22362 Lund, Sweden. Electronic address: richard.andersson@humlab.lu.se.
authors.forename: Richard
authors.initials: R
authors.lastname: Andersson
authors.affiliation: Department of Otorhinolaryngology Head and Neck Surgery, Clinical Sciences, Lund University, Lund, Sweden. Electronic address: mans.magnusson@med.lu.se.
authors.forename: Måns
authors.initials: M
authors.lastname: Magnusson
authors.affiliation: St. Erik Eye Hospital, Stockholm, Sweden; Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden. Electronic address: tony.pansell@ki.se.
authors.forename: Tony
authors.initials: T
authors.lastname: Pansell
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
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000328:Adult; D053483:Eye Movement Measurements / Q000295:instrumentation; D006801:Humans; D007908:Lens, Crystalline / Q000502:physiology*; D016014:Linear Models; D008297:Male; D011680:Pupil / Q000502:physiology*; D012438:Saccades / Q000502:physiology*
keywords: Accommodation; Eye tracking; Lens; Post-saccadic oscillation; Pupil