Analysis of language errors as function of treatment reveals mechanisms in bilingual aphasic lexical access

Kiran, S. 1 , Cabral, F. 1 , Sandberg, C. 1 & Tripodis, Y. 2

1 Boston University Speech Language and Hearing Sciences
2 Boston University School of Public Health

Bilingual aphasia is of increasing interest since more than half the world’s population is bilingual (Paradis, 1998). This study examines the evolution of naming errors in Spanish-English patients with aphasia receiving language therapy to improve their naming abilities (Edmonds & Kiran, 2006; Kiran & Roberts, 2009). This theoretically guided therapy is focused on facilitating access to the lexical items (e.g., cat) by strengthening corresponding semantic representations (semantic attributes of cat).
Naming errors produced by eight patients with aphasia during the course of treatment were categorized into subtypes such as (a) correct response in the non-target language, (b) semantic errors in the correct language or non-target language, (c) phonemic errors in the correct language or non-target language, (d) unrelated words in the correct language or non-target language, (e) perseverations etc. These types denote different mechanisms underlying the process of lexical access and show changing trends as the patient progresses through therapy. Time series models using eight patients were conducted with pre-stroke language proficiency and language of treatment entered into the model as covariates.
All patients showed evolution of errors as a function of treatment. First, the proportion of perseverations decreased as a function of treatment indicating that with therapy, the overall severity of the naming deficit decreased over time. Second, there is an increase in the proportion of semantic errors in the target language (e.g., dog for cat) and the non-target language (e.g., perro for cat) indicating increased access to semantically related neighbors for target as a function of therapy. These data are consistent with the suggestion that activation flows from the semantic system to the phonological system of both languages concurrently, indicating that lexical access is target language nonspecific (Costa & Santesteban, 2006; Finkbeiner et al., 2006) and extend this premise to lexical access in bilingual aphasia.