An examination of short-term memory deficits in nonfluent aphasia



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Martin (1987) has suggested that nonfluent aphasics have reduced ability to hold verbal information in short-term memory (STM) because of difficulty performing rehearsal. Two experiments were performed to test this hypothesis. In Experiment 1, recall of word sets was tested at 0, 5,10, and 20 seconds. More rapid decay was found in nonfluent aphasics than in fluent aphasics and controls, suggesting inability to regenerate information in STM in the nonfluent group. In Experiment 2, STM was compared for easy-to-articulate (EA) and difficult-to-articulate (DA) words. Controls and fluent aphasics showed an EA > DA superiority, assumedly due to more rapid rehearsal of the EA words. Nonfluent aphasics failed to show the EA > DA effect, suggesting impaired ability to use rehearsal. The results of the two experiments support the hypothesis of rehearsal-related STM deficits in nonfluent aphasia. A third experiment compared three measures of rehearsal skill as predictors of STM scores. None of the measures proved to be good predictors, and possible reasons for this finding were discussed. A fourth experiment compared pattern of performance across three STM tasks (serial recall, probe recognition, and missing digit), in an attempt to separate rehearsal-related STM deficits from other types of STM impairment. The serial recall task is known to draw on rehearsal, whereas the other two tasks do not. It was expected that aphasics with rehearsal difficulty would show poorest performance, relative to normals, on serial recall. This prediction was only partially confirmed: aphasics' scores were near the normal range for probe recognition, but well below normal for the serial recall and missing digit tasks. A final experiment tested claims that STM defects account for some aphasics' difficulty with sentence comprehension. Sentence comprehension was compared for two conditions: in the first, a printed sentence was in view during attempted comprehension; in the second, each sentence was presented one word at a time via computer screen. Comparison of performance on the two conditions yielded an estimate of the contribution of STM deficits to comprehension impairment. STM scores predicted performance on syntactically simple sentences with a heavy load of semantic information, but failed to predict performance on three types of syntactically complex sentences. The results suggest that STM defects play a determining role in comprehension impairment only for the former sentence type.



Aphasia, Memory disorders