Producing a sentence involves encoding a preverbal message into a grammatical structure by retrieving lexical items and integrating them into a functional (semantic-to-grammatical) structure. Individuals with agrammatism are impaired in this grammatical encoding process. However, it is unclear what aspect of grammatical encoding is impaired and how their grammatical encoding processes differ from those of healthy speakers. This study investigated how linguistic knowledge is used during real-time grammatical encoding processes in agrammatic, young, and older healthy speakers, based on two competing views of sentence production. In the incremental model, the unit of grammatical encoding is each lexical item. Speakers begin their utterance upon planning the first word and coordinate planning and speaking during speech. In the structural model, grammatical encoding proceeds in large chucks of linguistic information, building a hierarchical predicate structure (verb argument structure); thus, speakers plan up to the verb at least prior to speech onset.
Experiment 1 examined the production of a multi-word sentence with a pre-defined structure (‘the A and the B are above the C’) using eyetracking. Experiment 2 examined the production of transitive and unaccusative sentences (‘the man is rolling the wheel/ the wheel is rolling’) using lexical priming. Results showed that when producing a sentence in a pre-defined order in experiment 1, agrammatic speakers followed the incremental model like young and older speakers. However, in experiment 2 agrammatic speakers consistently encoded verb argument structure before speech onset for both transitive and unaccusative sentences, unlike young and older speakers.
The findings suggest that when grammatical encoding involves primarily lexicalization process (experiment 1), agrammatic speakers followed the incremental model. However, when both lexical retrieval and functional structure building processes are involved, agrammatic speakers followed the structural grammatical encoding model. Collectively, these findings suggest that the functional structure building process is likely to be compromised in agrammatism and verb argument structure is utilized actively from the earliest stage of sentence production in agrammatism. The findings also suggest that speakers' linguistic capacity and degree of incrementality interact in language production, and different forms of treatment may be used to train lexicalization and structure building processes in aphasia rehabilitation.
|Advisor:||Thompson, Cynthia K.|
|Commitee:||Marian, Viorica, Wong, Patrick, Yoshida, Masaya|
|Department:||Communication Sciences and Disorders|
|School Location:||United States -- Illinois|
|Source:||DAI-B 73/04, Dissertation Abstracts International|
|Subjects:||Linguistics, Speech therapy, Cognitive psychology|
|Keywords:||Agrammatism, Aphasia, Eyetracking, Grammatical encoding, Sentence production, Verb argument structure|
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