Patterns of visual dyslexia

This study reports two Hebrew-speaking individuals with acquired visual dyslexia. They made predominantly visual errors in reading, in all positions of the target words. Although both of them produced visual errors, their reading patterns crucially differed in three respects. KD had almost exclusively letter substitutions, and SF also made letter omissions, additions, letter position errors, and between-word migrations. KD had difficulties accessing abstract letter identity in single-letter tasks, and in letter naming, unlike SF, who named letters well. KD did not show lexical effects such as frequency and orthographic neighbourhood effects and produced nonword responses, whereas SF showed lexical effects, with a strong tendency to produce word responses. We suggest that these two patterns stem from two different deficits – KD has letter identity visual dyslexia, which results from a deficit in abstract letter identification in the orthographic-visual analysis system, yielding erroneous letter identities, whereas SF has visual-output dyslexia, which results from a deficit at a later stage, a stage that combines the outputs of the various functions of the orthographic-visual analyzer.