Sentence Comprehension in Aphasia: A Test of the Intervener Hypothesis
This dissertation investigates the factors that contribute to the sentence comprehension deficits exhibited by individuals with a particular acquired language disorder, Broca’s aphasia. Individuals with Broca’s aphasia (IWBA) have no difficulty comprehending sentences that conform to canonical (S-V-O) word order. However, difficulty arises for non-canonical sentences that contain syntactic dependencies. There are several accounts that attempt to explain these deficits. The focus of these accounts differs, some focus on syntax, others on lexical level deficits, and others on reduced cognitive resources. The current dissertation offers and focuses on a more recent account of the sentence processing deficits in IWBA, the Intervener Hypothesis (IH).
The IH suggests that difficulty comprehending sentences that contain syntactic dependencies arises when comprehension requires the crossing of an intervening noun phrase (NP), or intervener. The intervener causes similarity-based interference (SBI) because it is a possible element in the syntactic dependency. This dissertation tests the IH using sentences that contain a syntactic dependency inherent to unaccusative verbs.
Chapter 2 outlines pertinent linguistic concepts. Chapter 3 provides an overview of aphasia. Chapter 4 reviews psycholinguistic literature focusing on verb processing. Chapter 5 describes the sentence comprehension deficits observed in aphasia and theoretical accounts of these deficits. Chapter 6 details the account this dissertation focuses on, the IH. Chapter 7 investigates the time-course of lexical reactivation of unaccusative verbs during sentence processing. The results revealed that IWBA exhibit a time-course of lexical reactivation similar to neurologically unimpaired age-matched control (AMC) individuals indicating that IWBA are sensitive to the unaccusative property. Chapter 8 evaluates the IH by comparing final comprehension of sentences that contain unaccusative verbs in sentence constructions that contain an intervener and ones that do not. For IWBA, chance comprehension was found for sentences that contained an intervener suggesting SBI interferes with comprehension. Chapter 9 further investigates the pattern of comprehension observed in Chapter 8 using a real-time methodology, and also includes the first semantic manipulation of an intervener. The results revealed that SBI is observed during real time sentence processing of sentences that contain an unaccusative verb and an intervener, and that animacy reduced observed SBI.