About the role of visual field defects in pure alexia

Abstract

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.

“Seeing but not identifying”: pure alexia coincident with prosopagnosia in occipital arteriovenous malformation

“…These visual field defects are not Fig. 1 Visual fields at initial presentation showing slight right homonymous hemianopia causally related to the severity of visual recognition impairment [8]. Furthermore, the visual cortex plays a role in processing color vision.…”

Anatomical Connections of the Visual Word Form Area

“…Studies of patients with pure alexia (Dejerine, 1892;Cohen et al, 2003;Pflugshaupt et al, 2009), and functional brain imaging (Nobre et al, 1994;Jobard et al, 2003;Glezer and Riesenhuber, 2013) have put to light a region in the left ventral occipitotemporal cortex (the visual word form area; VWFA), which is thought to carry out this computation (Cohen et al, 2000). The VWFA then broadcasts orthographic information to language areas involved in central aspects of reading, including stored lexical information (the "deep" reading route), and grapheme-phoneme conversion (the "surface" reading route; Jobard et al, 2003;Price, 2012).…”

Top-Down Processing of Symbolic Meanings Modulates the Visual Word Form Area

“…This region, called the visual word form area (VWFA) (Cohen et al, 2000(Cohen et al, , 2002McCandliss et al, 2003), is shaped by reading experiences (Hashimoto and Sakai, 2004;Baker et al, 2007;Brem et al, 2010;Dehaene et al, 2010) and is not sensitive to low-level features of written words, such as size, position, font, or letter case (Dehaene et al, 2004;Binder et al, 2006;Vinckier et al, 2007;Glezer et al, 2009;Qiao et al, 2010;Braet et al, 2012). Neuropsychological studies have further revealed that the VWFA is necessary for reading, as the lesion of the VWFA is related to pure alexia with the hallmark feature of word-length effect (Mani et al, 2008;Pflugshaupt et al, 2009;Starrfelt et al, 2009). While extensive studies have focused on how the VWFA is tuned to visual properties of words, little is known about whether top-down influences modulate the VWFA.…”