The comprehension of sentences with unaccusative verbs in aphasia: a test of the intervener hypothesis.

BACKGROUND: It is well accepted that individuals with agrammatic Broca's aphasia have difficulty comprehending some sentences with filler-gap dependencies. While investigations of these difficulties have been conducted with several different sentence types (e.g., object relatives, Wh-questions), we explore sentences containing unaccusative verbs, which arguably have a single noun phrase (NP) that is base-generated in object position but then is displaced to surface subject position. Unaccusative verbs provide an ideal test case for a particular hypothesis about the comprehension disorder-the Intervener Hypothesis-that posits that the difficulty individuals with agrammatic Broca's aphasia have comprehending sentences containing filler-gap dependencies results from similarity-based interference caused by the presence of an intervening NP between the two elements of a syntactic chain. AIM: To assess a particular account of the comprehension deficit in agrammatic Broca's aphasia-the Intervener Hypothesis. METHODS & PROCEDURES: We used a sentence-picture matching task to determine if listeners with agrammatic Broca's aphasia (LWBA) and age-matched neurologically unimpaired controls (AMC) have difficulty comprehending unaccusative verbs when placed in subject relative and complement phrase (CP) constructions. OUTCOMES & RESULTS: We found above-chance comprehension of both sentence constructions with the AMC participants. In contrast, we found above-chance comprehension of CP sentences containing unaccusative verbs but poor comprehension of subject relative sentences containing unaccusative verbs for the LWBA. CONCLUSIONS: These results provide support for the Intervener Hypothesis, wherein the presence of an intervening NP between two elements of a filler-gap dependency adversely affects sentence comprehension.