Representation of linguistic rules in the brain: evidence from training an aphasic patient to produce past tense verb morphology.

We trained a patient with expressive aphasia and a deficit in phoneme-to-grapheme conversion to produce spoken English verbs with correct tense morphology. After training, he showed evidence of generalization to production of written regular, but not irregular, verbs in a sentence completion task. These data support dual-route, rule-based models within the brain for morphosyntactic operations.