Lexical biases in aphasic sentence comprehension: An experimental and corpus linguistic study

Background: This study investigates the role of lexical information in normal and aphasic sentence comprehension. Effects of verb biases in normal comprehension have been well documented in previous studies (e.g., Spivey-Knowlton & Sedivy, 1995; Trueswell, Tanenhaus, & Kello, 1993), but their role in aphasic language processing has largely been ignored (with the exceptions of Menn et al., 1998, and Russo, Peach, & Shapiro, 1998). Aims: The aim of the study is to test the lexical bias hypothesis, i.e., the hypothesis that sentence comprehension is influenced by lexical biases in aphasic listeners, as well as in normals. Method & Procedures: Using a sentence plausibility judgement task, we probe for sensitivity to verb transitivity bias, i.e., the likelihood, as estimated from corpus counts, that a verb will be transitive, rather than intransitive. Five normal controls and eighteen participants with aphasia (six with Broca's aphasia, four with Wernicke's aphasia, two with conduction aphasia, and six with anomic aphasia) are included in the study. Based on the lexical bias hypothesis, we predicted that participants would make more errors in sentences with a mismatch of verb bias and syntactic structure, such as a transitive sentence containing a verb with intransitive bias. Outcomes & Results: Both the group of normal controls and the mixed group of aphasic patients make significantly more errors on sentences in which there is a mismatch between verb bias and syntactic structure, as predicted by the lexical bias hypothesis. Specifically, patients with fluent aphasia types, particularly anomic aphasia, show a sensitivity to verb bias, contrary to earlier findings. Conclusions: These results are consistent with the view that lexical factors, not purely syntactic ones, are to blame for many previously observed patterns in aphasic comprehension. The results are further consistent with the view that many aphasic errors differ not qualitatively but quantitatively from normal comprehension errors.