Introduction
In usage-based approaches to language, grammar is viewed as an emergent phenomenon that derives from humans’ repeated exposure to individual instances of particular linguistic expressions (Bybee, 2006). Goldberg’s (1995) construction grammar is a version of usage-based grammar that treats language as an inventory of form-meaning pairings, termed constructions. Usage-based approaches to language predict that factors of language use, such as frequency of occurrence, affect processing at every level of the linguistic system, from sounds to sentences. This approach is gaining increasing recognition in the field of aphasiology, where sentence-level frequency effects have historically been described in terms of deficits (Gahl & Menn, 2016). The current research adopts a usage-based approach to language and contributes new data on the topic of verb and sentence processing in typical adults and adults with acquired aphasia.
Aims
This research investigated the effects of two frequency-based properties of verbs on language processing in adults, including the frequency of a verb as a single word, termed lexical frequency, and the frequency of a verb in a particular syntactic construction, termed construction frequency. Specifically, this project aimed: (1) to examine the effect of construction frequency and lexical frequency on sentence processing in adults; (2) to explore whether the pattern of performance from adults with acquired aphasia was similar to or divergent from the performance of typical adults; and (3) to consider how residual linguistic capabilities in participants with aphasia affected their performance in experimental tasks.
Methods
In Phase 1, 20 typical adults and four adults with acquired aphasia took part in a verbal fluency task in which they named verbs that could occur in eight unique syntactic constructions. Noun phrases were encoded as pronouns, so no semantic activation was available from the lexemes contained in sentence stimuli, and a blank space stood in place of the verb. For example, a sentence corresponding to the conative construction was presented as you ___ at us.
In Phase 2, 90 typical adults and 14 adults with acquired aphasia took part in a grammaticality judgement task and a sentence completion task. Participants silently read sentences like those in Phase 1 and were subsequently presented with a written verb. In the grammaticality judgement task, participants decided whether or not the verb could occur in the sentence stimulus. In the sentence completion task, participants replaced the blank space in the sentence stimulus with the given verb and produced the entire sentence aloud. Participants’ number of target responses and response times were measured in each task.
The frequency of verbs in Phase 2 varied along two dimensions. These independent variables included construction frequency and lexical frequency, each of which had two levels, namely, high frequency and low frequency. These four groups resulted in a factorial design, where conditions differed with respect to levels of construction frequency and lexical frequency.
Results
In Phase 1, the number of times typical participants generated verbs in response to syntactic constructions was more strongly related to verbs’ construction frequency than lexical frequency, for most constructions. Sentence stimuli successfully elicited verbs from participants with aphasia.
In Phase 2, typical participants showed an effect of construction frequency in the grammaticality judgement task and an effect of lexical frequency in the sentence completion task. These effects were moderated by construction and interactions. In general, group-level results from participants with aphasia were consistent with findings from typical participants. Some individuals with aphasia showed frequency effects to a greater or lesser extent than typical participants.
Conclusion
Results suggest that at the sentence level, the frequency of verbs as single words and the frequency of verbs in particular syntactic contexts affects language processing, depending on task demands. Findings confirm the predicted effect of linguistic experience on language use. Importantly, this project extends the number of investigations of pathological language undertaken in a usage-based linguistic framework. Results from participants with aphasia are discussed with reference to treatments for sentence processing deficits in aphasia, item selection for those treatments and theories of agrammatism.
