The effects of verb network strengthening treatment on sentence production in individuals with aphasia
Some persons with aphasia exhibit a selective verb deficit, which results in a reduced ability to produce verbs in most contexts. A functional level (Bock & Levelt, 1994) impairment may result in impaired sentence production because the verb serves as the semantic-syntactic interface of a sentence. This interface is related to a verb’s relationship with its arguments/thematics. Arguments fill the syntactic slots of subject and object, and those same words serve as thematic roles by referring to who does what to whom. The current study investigates the effect of Verb Network Strengthening Treatment (VNeST) on sentence production using a single subject experimental design across subjects in 4 participants, 2 with nonfluent aphasia and 2 with fluent aphasia. Participants received semantic treatment aimed at re-strengthening the connections between a verb (e.g., measure) and related thematic pairs that refer to the doer and receiver of the action (e.g., carpenter/lumber, chef/sugar). The ability to produce thematic role pairs for trained verbs was tested during treatment while generalization to the ability to produce sentences containing a subject, verb, and object in a picture description task with trained verbs (e.g., The carpenter is measuring the stairs.) and semantically related untrained verbs (e.g., The nurse is weighing the baby.) was monitored. In addition, pre- and post-treatment single word retrieval of verbs (The Northwestern Verb Production Battery (NVPB) (Thompson, 2002)) and nouns (The Boston Naming Test (Goodglass & Kaplan, 1983)) was examined as well as sentence production abilities in unrelated picture description (NVPB) and constrained connected speech tasks. All participants met treatment criteria and exhibited generalization to sentence production with sentences containing trained and semantically related untrained verbs. Participants 1, 2, and 3 exhibited improvements on all pre- and post-treatment measures, including connected speech. Participant 4 exhibited gains on multiple measures but did not show improvement in connected speech. These findings indicate that treatment aimed at strengthening the verb network results in improved word retrieval in naming and sentence production across multiple tasks. Theoretical and clinical implications regarding the impact of using VNeST on rehabilitation of sentence production deficits in aphasia are discussed.