Visual errors in acquired dyslexia: Evidence for cascaded lexical processing

A single case study is reported of the dyslexic and only mildly aphasic pat ient AT who almost exclusively produced visually related errors in reading aloud. His performance in the auditory modality (auditory comprehension, ph oneme discrimination) was nearly perfect, his repetition and oral naming ab ilities for single-word production were almost unimpaired. Closer examinati ons of his reading disturbance revealed a deficit in visual processing of o rthographic materials which extended to Arabic numbers and other nonlinguis tic symbols. Contrasting with this prelexical deficit, AT's performance in reading aloud and also in visual lexical decision was strongly influenced b y factor imageability, which could not be attributed to a general semantic deficit. It is argued that AT's pattern of reading performance (prelexical visual impairment and imageability effects on his visual errors) cannot be accounted for by a discrete stage model of lexical-orthographic processing allowing only one lexical candidate to be selected. Rather, the case AT pro vides empirical evidence for cascaded processing between the lexical and se mantic level. The cascade account suggests that not only one but several vi sually related lexical candidates activate their corresponding semantic rep resentations with different degrees of imageability.