title: Vergence responses to vertical binocular disparity during lexical identification.
abstract: Humans typically make use of both eyes during reading, which necessitates precise binocular coordination in order to achieve a unified perceptual representation of written text. A number of studies have explored the magnitude and effects of naturally occurring and induced horizontal fixation disparity during reading and non-reading tasks. However, the literature concerning the processing of disparities in different dimensions, particularly in the context of reading, is considerably limited. We therefore investigated vertical vergence in response to stereoscopically presented linguistic stimuli with varying levels of vertical offset. A lexical decision task was used to explore the ability of participants to fuse binocular image disparity in the vertical direction during word identification. Additionally, a lexical frequency manipulation explored the potential interplay between visual fusion processes and linguistic processes. Results indicated that no significant motor fusional responses were made in the vertical dimension (all p-values>.11), though that did not hinder successful lexical identification. In contrast, horizontal vergence movements were consistently observed on all fixations in the absence of a horizontal disparity manipulation. These findings add to the growing understanding of binocularity and its role in written language processing, and fit neatly with previous literature regarding binocular coordination in non-reading tasks.
authors.affiliation: School of Psychology, University of Southampton, Highfield Campus, Southampton SO17 1BJ, UK. Electronic address: M.Nikolova@soton.ac.uk.
authors.forename: M
authors.initials: M
authors.lastname: Nikolova
authors.affiliation: Leibniz Research Centre for Working Environment and Human Factors, Ardeystrasse 67, D-44139 Dortmund, Germany. Electronic address: jainta@ifado.de.
authors.forename: S
authors.initials: S
authors.lastname: Jainta
authors.affiliation: School of Psychology, University of Southampton, Highfield Campus, Southampton SO17 1BJ, UK. Electronic address: hib@soton.ac.uk.
authors.forename: H I
authors.initials: HI
authors.lastname: Blythe
authors.affiliation: School of Psychology, University of Southampton, Highfield Campus, Southampton SO17 1BJ, UK. Electronic address: M.O.Jones@soton.ac.uk.
authors.forename: M O
authors.initials: MO
authors.lastname: Jones
authors.affiliation: School of Psychology, University of Southampton, Highfield Campus, Southampton SO17 1BJ, UK. Electronic address: S.P.Liversedge@soton.ac.uk.
authors.forename: S P
authors.initials: SP
authors.lastname: Liversedge
mesh_terms: D000328:Adult; D003290:Convergence, Ocular / Q000502:physiology*; D005133:Eye Movements / Q000502:physiology; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans; D011932:Reading; D015357:Vision Disparity / Q000502:physiology*; D015348:Vision, Binocular / Q000502:physiology*
keywords: Binocular fusion; Fixation disparity; Reading; Vertical vergence