Do all visual deficits cause pure alexia? Dissociations between visual processing and reading suggest “no”

•Patients with pure alexia or PCA were compared on word reading and visual processing.•The alexic patients were impaired on reading but not visual processing.•The PCA patient was impaired on visual processing but not reading. Pure alexia is a deficit of reading affecting the ability to process a word’s letters in parallel. Instead, a slow, effortful letter-by-letter reading strategy is employed. It has been claimed that a visual impairment caused the reading impairment. The present study compares visual processing and word reading of a patient with severe visuospatial deficits due to probable posterior cortical atrophy (PCA) to two patients with pure alexia. A double dissociation emerged between visual processing and word reading: The participant with PCA was severely impaired in all visual tasks but read fluently while the patients with pure alexia read slowly but exhibited better preserved visual processing. It is concluded that a visual impairment does not inevitably lead to pure alexia, and that this syndrome is more plausibly conceived of as an orthographic deficit. In addition, the PCA patient’s hypometabolism was assessed, and the interaction of the dorsal and ventral visual stream in word reading is discussed.