Professor, Cognitive Sciences
University of California, Irvine
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Using cognitive models to understand how semantic memory changes with impairment*
Understanding how semantic memory changes because of impairment is a basic challenge for cognitive science, and an important question for society. A rich source of real-world behavioral evidence to address this challenge is provided by memory tests routinely administered in clinical care settings. We use tens of thousands of test results from two tasks in the Mild Cognitive Impairment Screen (MCIS). These tests were taken by thousands of people ranging from healthy controls to patients with different levels of impairment and dementia. The first memory task requires people to identify the “odd one out” of a set of three animal names. The second task is a surprise free recall of all of the animal names presented in the first task. We develop novel cognitive models of both the odd-one-out choices and the free recall behavior. This model-based approach allows us to test different hypotheses about whether and how semantic memory changes as impairment increases. For the odd-one-out task, contrary to previous claims, we find no evidence that the semantic representation of the animals changes. Instead, changes in performance can be explained in terms of worsening access to memory and the use of compensating response strategies. For the free recall task, we find that access to episodic information worsens with mild cognitive impairment but semantic information remains intact. As impairment worsens to become dementia, however, access to semantic information is also lost. We emphasize how the use of cognitive models increases the theoretical insight into the changes in semantic memory, and provides a fine-grained clinical measurement capability that can be used in detection, diagnosis, and treatment.
* Joint work with Holly Westfall