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Abstract

The goal of this thesis is to identify the underlying impairments in aphasic disorders of auditory comprehension and repetition. The findings are interpreted within a cognitive neuropsychological framework. Models of normal language processing are discussed in the light of this evidence.

Information processing models of the lexicon attempt to specify the stages of processing necessary for auditory comprehension, as well as different routes by which words can be repeated. Twenty fluent aphasic patients were used in the study.

It was found that the patients did show qualitative differences in auditory word comprehension. Five levels of impairment were identified: word-sound deafness, word-for deafness, word-meaning deafness, a central semantic disorder and a disorder specific to abstract words. It was concluded that abstract words are more sensitive to impairment than concrete words.

Word imageability was investigated in more detail in a number of experiments with a word meaning deaf patient (DRB). It was shown that his impairment is one of access from the input lexicon to the semantic system. The impairment results in under-specification in the semantic system, and an extremely robust effect of imageability in DRB's ability to comprehend and repeat auditorily presented words. This effect is not item-specific. Intriguingly, the results also suggest that DRB has an anomia for words of low imageability.

In a subsequent section, the patients' abilities in repetition are investigated. Two routes for repetition are identified, a sub-lexical and a lexical/semantic route. Phonologically related errors arising in the former route tend to be non-words, occur particularly on longer words, and the errors tend to be in the final position of the string. Phonological errors arising in the lexical/semantic route are real words, tend to be higher in frequency than the stimulus items, and occur particularly on shorter words.

The relationship between repetition and auditory short term memory is considered by further experiments with DRB. It is argued that sub-lexical repetition utilises the auditory short term memory system. DRB's sub-lexical repetition and his immediate serial recall are enhanced by lip read information. A model of repetition and auditory short-term memory is presented. It is argued that the system requires different input and output phonological codes, suggesting separate input and output lexicons. With the specification of how lexical information supports immediate serial recall, it is argued that there is no requirement for a direct, lexical, non-semantic route in repetition.

Publication Type:	Thesis (Doctoral)
Subjects:	H Social Sciences Q Science > QP Physiology R Medicine > RZ Other systems of medicine
Departments:	Doctoral Theses School of Health & Psychological Sciences > Language & Communication Science School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses

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