REPRESENTATION OF GRAMMATICAL CATEGORIES OF WORDS IN THE BRAIN

We report the performance of a patient who, as a consequence of left f rontal and temporoparietal strokes, makes far more errors on nouns tha n on verbs in spoken output tasks, but makes far more errors on verbs than on nouns in written input tasks. This double dissociation within a single patient with respect to grammatical category provides evidenc e for the hypothesis that phonological and orthographic representation s of nouns and verbs are processed by independent neural mechanisms. F urthermore, the opposite dissociation in the verbal output modality, a n advantage for nouns over verbs in spoken tasks, by a different patie nt using the same stimuli has also been reported (Caramazza & Hillis, 1991). This double dissociation across patients on the same task indic ates that results cannot be ascribed to ''greater difficulty'' with on e type of stimulus, and provides further evidence for the view that gr ammatical category information is an important organizational principl e of lexical knowledge in the brain.