Approximately one-third of stroke survivors in the United States suffer from aphasia, a disorder that affects the ability to use and/or understand language. Word-retrieval impairments are a cardinal symptom of aphasia. Noun-retrieval deficits have long been studied, but verbs have received much less attention. Despite this, approximately 70% of people with aphasia have verb-retrieval deficits, which are highly predictive of success in everyday communication. Behavioral treatments targeting verb retrieval result in improved language function and communicative effectiveness, but the underlying mechanisms and predictors of response to such treatments are not understood. The proposed study aims to addresses this gap by investigating behavioral, neuroanatomical, and cue-type variables that characterize verb-retrieval impairments and promote successful verb retrieval in people with aphasia. The first objective of this research is to characterize neuroanatomical differences that predict how well individuals with aphasia retrieve linguistic (verb) information versus conceptual (action) information. Performance on a validated behavioral battery of verb and (picture-based) action stimuli will be compared to both white-matter and gray-matter neuroanatomical variables. This comparison will test competing models of the neural basis of language and conceptual representations, and of aphasic language deficits. Classic cognitive- linguistic accounts hypothesize that people with aphasia will perform poorly on linguistic tasks, but not conceptual tasks. They further predict that severity of linguistic impairments will be associated with lesions exclusively to language-related brain networks. In contrast, grounded cognition accounts predict that people with aphasia will have impairments in both linguistic and conceptual tasks, hypothesizing that this occurs due to damage in language- or action-related brain networks, which jointly support performance in such tasks. The second objective is to investigate whether people with and without aphasia rely on linguistic versus conceptual information during verb retrieval. People will retrieve verbs in response to either linguistically- or conceptually-related cues. A primed verb-naming experiment will test how these two information types drive verb-retrieval performance in a task that prioritizes linguistic processing (?Name the word you see on the screen?). Based on previous findings, it is hypothesized that healthy participants will show greater facilitation for linguistically-related cues than for conceptually-related cues in such naming tasks. People with aphasia are expected to show greater facilitation for conceptual cues in the verb-naming task if they have successfully adapted to their language impairments. Subsequent analyses will identify person-level traits (neuroanatomical, behavioral) that predict which cues facilitate verb retrieval in people with aphasia, at both the group and the individual level. This research will provide evidence that can advance neurocognitive models, inform clinical decision-making, and guide selection of verb-retrieval interventions.
The proposed research will measure conceptual and linguistic aspects of verb retrieval in individuals with aphasia and assess whether person-level behavioral and neurological variables can predict response to cues that facilitate verb retrieval. Results will inform cognitive models of how conceptual and linguistic knowledge is organized in the brain and used during normal and disordered language processing. These findings will strengthen our understanding of verb-retrieval deficits, a pervasive impairment associated with lasting communicative disability and lower quality of life.
