Brain Advance Access published online on June 4, 2009
Brain, doi:10.1093/brain/awp141
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About the role of visual field defects in pure alexia
1 Perception and Eye Movement Laboratory, Department of Neurology, Inselspital, Bern University Hospital and University of Bern, Switzerland 2 Perception and Eye Movement Laboratory, Department of Clinical Research, Inselspital, Bern University Hospital and University of Bern, Switzerland 3 Division of Cognitive and Restorative Neurology, Department of Neurology, Inselspital, Bern University Hospital and University of Bern, Switzerland 4 Section of Neuropsychology, Centre for Neurology, Hertie-Institute for Clinical Brain Research, Eberhard Karls University, Tübingen, Germany
Correspondence to:
Prof. René M. Mueri, MD, Perception and Eye Movement Laboratory, Departments of Neurology and Clinical Research, University Hospital, 3010 Bern, Switzerland E-mail: rene.mueri{at}insel.ch
Pure alexia is an acquired reading disorder characterized by a disproportionate prolongation of reading time as a function of word length. Although the vast majority of cases reported in the literature show a right-sided visual defect, little is known about the contribution of this low-level visual impairment to their reading difficulties. The present study was aimed at investigating this issue by comparing eye movement patterns during text reading in six patients with pure alexia with those of six patients with hemianopic dyslexia showing similar right-sided visual field defects. We found that the role of the field defect in the reading difficulties of pure alexics was highly deficit-specific. While the amplitude of rightward saccades during text reading seems largely determined by the restricted visual field, other visuo-motor impairments—particularly the pronounced increases in fixation frequency and viewing time as a function of word length—may have little to do with their visual field defect. In addition, subtracting the lesions of the hemianopic dyslexics from those found in pure alexics revealed the largest group differences in posterior parts of the left fusiform gyrus, occipito-temporal sulcus and inferior temporal gyrus. These regions included the coordinate assigned to the centre of the visual word form area in healthy adults, which provides further evidence for a relation between pure alexia and a damaged visual word form area. Finally, we propose a list of three criteria that may improve the differential diagnosis of pure alexia and allow appropriate therapy recommendations.
Key Words: reading; eye movements; visual field defect; pure alexia; hemianopic dyslexia
Abbreviations: LBL, letter-by-letter; VWFA, visual word form area; WLE, word length effect; wpm, words per minute
Received November 21, 2008. Revised February 5, 2009. Accepted April 24, 2009.
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