Degree Name

Doctor of Philosophy


Department of Psychology


Semantic memory impairments have been hypothesised to underlie many of the language difficulties reported in probable Alzheimer's Disease, such as naming and verbal fluency. Contention exists regarding whether observed difficulties constitute a semantic storage impairment, or difficulty in the access and processing of relatively intact semantic knowledge. This study investigated the integrity of several types of semantic associations, namely, category co-members, functional associates and sensory associates in six single case studies of mild probable Alzheimer's Disease. A semantic priming pronunciation task, designed to minimise subject-initiated strategies (SOA of 350 ms and relatedness proportion of .15), and a series of off-line neuropsychological measures were used. The results supported the hypothesis of partial impairment in semantic memory in some, but not all of the cases. Both hyperpriming and significant underpriming were observed in four out of the six cases in comparison to an age and education matched control group. Where semantic memory impairment was observed, dissociation between types of semantic knowledge was found. Relative preservation of functional associate priming, accompanied by impairment in both category co-member and sensory associate priming was found in one probable Alzheimer's Disease subject and a similar trend was noted in a further two cases. In comparison, another subject displayed priming in the functional associate condition which approached significance, while priming in the sensory associate condition was preserved. The results suggested heterogeneity of impairment in the mild stage of Alzheimer's Disease, and it was hypothesised that subgroups may exist with respect to their pattern of impairment in semantic memory. It is suggested that models of semantic memory storage must accommodate observations of dissociation between different types of semantic knowledge.