title: Estimation of cortical magnification from positional error in normally sighted and amblyopic subjects.
abstract: We describe a method for deriving the linear cortical magnification factor from positional error across the visual field. We compared magnification obtained from this method between normally sighted individuals and amblyopic individuals, who receive atypical visual input during development. The cortical magnification factor was derived for each subject from positional error at 32 locations in the visual field, using an established model of conformal mapping between retinal and cortical coordinates. Magnification of the normally sighted group matched estimates from previous physiological and neuroimaging studies in humans, confirming the validity of the approach. The estimate of magnification for the amblyopic group was significantly lower than the normal group: by 4.4 mm deg(-1) at 1° eccentricity, assuming a constant scaling factor for both groups. These estimates, if correct, suggest a role for early visual experience in establishing retinotopic mapping in cortex. We discuss the implications of altered cortical magnification for cortical size, and consider other neural changes that may account for the amblyopic results.
authors.affiliation: School of Psychology, University of Nottingham, Nottingham, United Kingdom.
authors.forename: Zahra
authors.initials: Z
authors.lastname: Hussain
authors.affiliation: School of Psychology, University of Nottingham, Nottingham, United Kingdom.
authors.forename: Carl-Magnus
authors.initials: CM
authors.lastname: Svensson
authors.affiliation: MRC Institute of Hearing Research, Nottingham, United Kingdom.
authors.forename: Julien
authors.initials: J
authors.lastname: Besle
authors.affiliation: School of Psychology, University of Nottingham, Nottingham, United Kingdom.
authors.forename: Ben S
authors.initials: BS
authors.lastname: Webb
authors.affiliation: School of Optometry and Vision Science, University of Bradford, Bradford, United Kingdom.
authors.forename: Brendan T
authors.initials: BT
authors.lastname: Barrett
authors.affiliation: School of Psychology, University of Nottingham, Nottingham, United Kingdom.
authors.forename: Paul V
authors.initials: PV
authors.lastname: McGraw
mesh_terms: D000328:Adult; D000550:Amblyopia / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012160:Retina / Q000503:physiopathology*; D014793:Visual Cortex / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology*; D055815:Young Adult
keywords: E2; alignment; amblyopia; bisection; distortion; localization; retinotopy; strabismus