UC Irvine

It is well established that Alzheimer’s disease leads to a decline in both episodic and semantic memory. My research focuses on semantic memory and uses cognitive models to try to understand the nature of changes in memory as the disease progresses. Applying cognitive models, I am able to make inferences about underlying memory processes that cannot be measured directly from behavioral data.

In Chapter 1, I evaluate theories of the change in semantic memory caused by Alzheimer's disease. Many such theories characterize the cognitive decline associated with Alzheimer’s disease as an elaborate combination of systematic changes to underlying mental representations and to attention processes. I conclude that a simpler theory of Alzheimer’s disease as interfering with the patient’s ability to retrieve information stored in memory can account for the data just as well as more complex theories.

In Chapter 2, I investigate changes in episodic memory associated with Alzheimer’s disease. I specifically focus on the order of free recall among Alzheimer's patients and develop a regression model that includes semantic similarity and various word-level characteristics as predictors. I demonstrate that the semantic similarity between items and the number of times an item is encountered are potentially important predictors of free recall output.

In Chapter 3, I explore how semantic memory can influence episodic memory recall. I extend the SIMPLE model of memory and apply it to three groups of patients including healthy controls, people with mild cognitive impairment, and people with Alzheimer’s dementia. I compare and contrast the relative influence of temporal similarity and semantic similarity on free recall performance within the three patient groups. As cognitive impairment increased, the ability to distinguish between items that were temporally similar decreased, as did the use of semantic similarity as a recall cue.

Collectively, the work in this dissertation shows that cognitive models of memory can provide a more complete understanding of the changes in semantic memory that occur with cognitive impairment.