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Abstract
Background: The study explores the ability of fluent and non-fluent aphasic patients to produce verbs using the appropriate argument structure, i.e., a feature specifying the number and type of participants in the event described by the verb. According to Chomsky's Minimalist Program (Citation1995), the lexical entry of a verb contains information about the number of arguments and the thematic roles assigned, which is then mapped onto the sentence argument structure, while Bock and Levelt's (Citation1994; see also Levelt, Roelofs, & Meyer, Citation1999) model of lexical production assumes that the information regarding verb argument structure (VAS) is part of the lemma and is accessed before the retrieval of the phonological word form, i.e., the lexeme.
Aim: Participants were tested to investigate their ability to map thematic information onto the corresponding syntactic argument structure.
Methods & Procedures: Seven aphasic patients (five suffering from non-fluent aphasia with agrammatism and two from fluent aphasia) and ten neurologically unimpaired individuals participated in the study. They were given a picture description task formulated in two conditions: in the first condition they were asked to provide a free description of the image, while in the second condition they had to complete the sentence structure provided by the examiner. Patients showing deficits in verb production were also tested for the use of prepositions within prepositional compounds and in a sentence context.
Outcomes & Results: Four agrammatic patients and one fluent aphasic patient scored a high rate of argument structure errors in the selection of the appropriate verb, which was employed with an incorrect argument structure. Furthermore, these patients tended to substitute rather than to omit prepositions when required to fill the gap in a sentence.
Conclusions: Our results indicate an impaired access to (VAS) and/or in mapping the thematic role information onto the syntactic argument structure. This deficit, which was found in both the agrammatic and the fluent aphasic patients, conflicts with an alternative interpretation of verb production errors in terms of omission of the preposition introducing the manner adjunct. Data support the hypothesis of retrieval of the verb lexeme without prior access to the corresponding lemma, where information about argument structure is stored.
This research was partially supported by a Grant from the Regione Lombardia to E.B. and from the MIUR to C.L. We are grateful to Prof. Germano Rossi for the helpful suggestions given regarding the statistical analyses, and to Prof. Alfonso Caramazza for his insightful comments on a previous version of the manuscript.
Notes
1This is not the case for Italian meteorological verbs such as piovere (piove, [it] rains) and for impersonal verbs such as sembrare (sembra, [it] seems), which do not take a subject; furthermore, the Italian language allows subject pro-drop, i.e., the omission of subject pronouns.
2Italian has a very rich morphology in which citation forms are also inflected; therefore, an omission of bound morphemes often results in the production of non-lexical roots.
3Following Chomsky's Principles and Parameters Theory (Chomsky & Lasnik, Citation1993), a sentence may be represented as a tree with nodes and branches. Each node splits into a head, a complement, and a specifier. A precise hierarchy is assumed to govern the syntactic tree, which dictates the order in which the nodes occur; for example, the CP node, which hosts complementisers (such as that) and question morphemes (such as who and what), projects to the TP node, which is responsible for the tense inflection of the verb.
4Contrary to the English verb to give, which can take a double argument structure, either transitive (+ complement) or ditransitive (Mary gives the book to John and Mary gives John the book), in Italian the verb dare takes only one argument structure, always requiring a prepositional phrase introduced by a (to).
