The role of argument structure in the production of nouns and verbs

The study reports an investigation on the role of argument structure complexity in the production of nouns and verbs in three Italian agrammatic patients. The patients, all showing a clear noun/verb dissociation in the assessment tests, were requested to produce either nouns or verbs in a picture naming task. Four sets of words were selected to be produced in the naming task: non-argumental nouns (e.g., medaglia-medal), argumental nouns (e.g., pianto-crying), one-place argument verbs (e.g., dormire-to sleep), and two-place argument verbs (e.g., sparare-to shoot). The performance of the three patients was almost identical. All made reliably fewer errors in the production of non-argumental nouns than in the production of verbs, thus replicating with the new materials the initially observed dissociation. Moreover, they made fewer errors with one-place than with two-place argument verbs, and with non-argumental than with argumental nouns. Finally, in contrast with the previously observed noun/verb dissociation, when their ability to produce argumental nouns and verbs was compared, no reliable difference was found. The results indicate that argument complexity may affect the ability of agrammatic patients to produce words. It is argued that since argument complexity is necessarily associated with verbs and only rarely with nouns, unless special attention is paid, argument complexity effects are easily confounded with grammatical class effects, possibly leading to erroneous interpretations of patients' performance.