Cognitive and neural mechanisms underlying reading and naming: evidence from letter-by-letter reading and optic aphasia.

We report detailed analysis of language performance in a patient, RMI, a 55-year-old man who presented with a homonymous hemianopsia, optic aphasia, and alexia without agraphia (with letter-by-letter reading) acutely after stroke. MRI showed infarct in the left occipital and medial temporal lobe and hypoperfusion of the entire posterior cerebral artery territory, including the splenium. Extensive language testing revealed severely impaired picture naming and oral reading, with relatively spared tactile naming and recognition of orally spelled words, consistent with impaired access to lexical and semantic representations from vision. In addition, he had a milder deficit in accessing lexical representations for output from all input modalities. RMI's execution of various language tasks provided considerable insight into the mechanisms that underlie oral reading. His performance indicated that both semantic access and orthographic to phonologic conversion mechanisms were partially intact. When information from these two impoverished systems was coupled (the picture of an object presented with its written name), his ability to read/name improved significantly, consistent with the hypothesis that partially accessed semantic information from vision can combine with partially accessed sublexical orthographic to phonologic conversion mechanisms to access phonological representations for output. Furthermore, his written word and picture recognition improved to normal at a time when magnetic resonance perfusion imaging demonstrated reperfusion of the splenium. We interpret these results, as well as results from previous studies in the literature, within a model of the neural regions critical for various cognitive processes underlying reading.