The processing of morphology and syntax in aphasia: A test of the fast decay and slow activation hypotheses

Abstract

Two tasks were designed to test the hypothesis that the syntactic processing deficit of non-fluent agrammatic aphasic patients may be due to either the fast decay or slow activation of syntactic information. Eight non-fluent aphasics, 11 fluent aphasics, and 15 age-matched normal control subjects participated in two auditory lexical decision tasks as well as a grammaticality judgement task. In three types of sentence structures the sentence-final word created either a grammatical sentence or a violation of a particular syntactic rule or constraint. To examine possible deficits in computational speed, the interval between the sentence frame and the sentence-final target word was set at either 100 ms (short ISI) or 1000 ms (long ISI) in the lexical decision tasks. Increased reaction time to targets in ungrammatical sentences is indicative of sensitivity to syntactic violations. With fast decay of syntactic information, sensitivity would be predicted at short but not long ISIs. With slow activation, sensitivity would be expected at long but not short ISIs. Surprisingly, results indicated that all three groups of subjects demonstrated comparable patterns of sensitivity to grammaticality as reflected in increased latencies to target words in ungrammatical contexts. The findings do not provide support for either the fast decay or the slow activation hypothesis. Possible reasons for the unexpected findings are considered.