Teasing Apart the Contribution of Memory and Language Impairments in Alzheimer's Disease

An Online Study of Sentence Comprehension

Sentence comprehension is a complex activity that depends on many different component skills, including the ability to understand individual words, integrate the meanings of adjacent words, and interpret grammatical structures. Tests of sentence comprehension, such as sentence-picture matching, require patients to use all of these linguistic abilities and to remember the meaning of a sentence while performing the task. Therefore, it is often difficult to determine, in cases of comprehension impairment, precisely why a sentence is misunderstood. This is particularly true for patients with Alzheimer's disease, who have both severe semantic and working memory disorders. This paper presents data from an online (cross-modal naming) sentence comprehension test designed to minimize the memory requirements of test performance-while still assessing the ability of patients to integrate the meanings of two nouns and a verb in a sentence. This task has the advantages of measuring comprehension as the sentence is processed and not requiring the subjects to reflect on, or make judgments about, the sentence meaning afterward. The results suggest that patients with Alzheimer's disease can successfully process sentences with relatively complex meanings as they hear them. Therefore, these patients' sentence comprehension deficits are likely due to an inability to maintain active information in memory and not due to a purely semantic impairment.

Key Words: Alzheimer, sentence, comprehension, memory, language, working memory

Submitted on August 8, 1997
Accepted on November 26, 1997

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