title: Visual speech perception in foveal and extrafoveal vision: further implications for divisions in hemispheric projections.
abstract: When observing a talking face, it has often been argued that visual speech to the left and right of fixation may produce differences in performance due to divided projections to the two cerebral hemispheres. However, while it seems likely that such a division in hemispheric projections exists for areas away from fixation, the nature and existence of a functional division in visual speech perception at the foveal midline remains to be determined. We investigated this issue by presenting visual speech in matched hemiface displays to the left and right of a central fixation point, either exactly abutting the foveal midline or else located away from the midline in extrafoveal vision. The location of displays relative to the foveal midline was controlled precisely using an automated, gaze-contingent eye-tracking procedure. Visual speech perception showed a clear right hemifield advantage when presented in extrafoveal locations but no hemifield advantage (left or right) when presented abutting the foveal midline. Thus, while visual speech observed in extrafoveal vision appears to benefit from unilateral projections to left-hemisphere processes, no evidence was obtained to indicate that a functional division exists when visual speech is observed around the point of fixation. Implications of these findings for understanding visual speech perception and the nature of functional divisions in hemispheric projection are discussed.
authors.affiliation: Department of Psychology, Zayed University, Dubai, UAE.
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Jordan
authors.affiliation: Department of Psychology, Zayed University, Dubai, UAE.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Sheen
authors.affiliation: School of Psychology, University of Leicester, Leicester, United Kingdom.
authors.forename: Lily
authors.initials: L
authors.lastname: Abedipour
authors.affiliation: School of Psychology, University of Leicester, Leicester, United Kingdom.
authors.forename: Kevin B
authors.initials: KB
authors.lastname: Paterson
mesh_terms: D000293:Adolescent; D000328:Adult; D005133:Eye Movements; D005145:Face / Q000502:physiology; D005149:Facial Expression; D005403:Fixation, Ocular / Q000502:physiology; D005584:Fovea Centralis / Q000502:physiology*; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D010364:Pattern Recognition, Visual / Q000502:physiology*; D013060:Speech; D013067:Speech Perception / Q000502:physiology*; D006113:United Kingdom; D014785:Vision, Ocular / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult