DISORDERS OF LEXICAL ACCESS IN SPEECH PRODUCTION

Harvard University, Cambridge MA

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Abstract

The goal of the proposed research is to understand the nature of naming and word-finding difficulties in aphasia. The objective is to explain patterns of word production deficits in terms of damage to the cognitive/linguistic mechanisms that underlie normal word production, and then to use this knowledge toward the development of a theory of the functional organization of the brain. Two general questions will be addressed: 1) What are the causes of the grammatical class deficits? And, 2) what are the causes of the different error types in naming deficits? More specific questions include: 1) Are there different subtypes of grammatical class disorders? 2) What is the relationship between impairments in the production of nouns and the ability to produce noun phrase structure? 3) Are the causes of access failure for nouns and verbs the same as for failure to retrieve adjectives? What are the causes of failure to access function words and inflectional morphology? 4) Are different mixtures of error types the result of global lesions that affect equally all stages of the lexical access process or are they the result (at least in some cases) of different lesions to different stages of the process? 5) What relationship is there between the distribution of error types in naming and other tasks (such as reading, repetition, comprehension, etc.)? These and related questions will be addressed through a three-pronged program of research. The most important part involves the detailed investigation of the word and phrase processing performance of English and Italian monolingual aphasics and Spanish-Catalan bilingual aphasics. The two other components of the research involve the computational modeling of the patients' patterns of word production deficits and the experimental investigation of normal subjects' word and phrase production performance. This integrated approach to the study of lexical access deficits should provide important information about the organization and processing structure of the lexicon and about the functional causes of word production disorders in aphasia. These are necessary components of the larger goal of understanding the functional architecture of the brain and for developing intervention strategies for remedial training of aphasia.