Recovery of sentence production following language treatment in aphasia: Evidence from eyetracking
Introduction. Sentence production impairments in aphasia are associated with abnormal online processes, e.g., impaired thematic mapping and reduced incrementality (Cho & Thompson, 2010; Lee, Yoshida, & Thompson, 2015). Little is known about how language treatment affects online sentence processing in people with aphasia, e.g., whether improved sentence production is associated with re-learning of normal processes and/or the use of alternative strategies.
Methods. The present study used eyetracking to examine changes in sentence production resulting from a 12-week language treatment program focused on passive sentences (Treatment of Underlying Forms; Thompson & Shapiro, 2005). In two pre-treatment and two post-treatment test sessions, nine participants with mild-to-moderate agrammatic aphasia repeated visually- and auditorily-presented prime sentences (active or passive, e.g., The chimp was lifting/lifted by the gorilla), and then used the same verb and sentence type to describe an event picture (e.g., a man lifting a woman). We examined effects of language treatment on picture description responses, specifically (1) accuracy, (2) speech durations for each sentence region (e.g., [PreN1 The [N1 man was] [V lifting/lifted by the] [N2 woman END]), and (3) eye movements to the pictured Agent and Theme during each sentence region, reflecting lexical and grammatical encoding processes. Ten unimpaired older adults also performed the task to identify normal performance patterns. Data were analyzed using mixed-effects regression.
Results. The unimpaired adults performed with high accuracy (Fig. 1A) and their eye movements indicated encoding of N1 during the PreN1 region (i.e., fixations on the Agent in actives and Theme in passives) and encoding of N2 during the N1 and V regions (Fig. 1B). In participants with aphasia, picture description accuracy improved significantly with treatment for passive sentences, but did not change for actives (Fig. 1A). No treatment-related changes in speech durations were observed for either structure. Pre-treatment eye movements were qualitatively abnormal, and did not differ between passive and active trials in any sentence region (Fig. 1C). Post-treatment, eye movements were qualitatively more similar to those of unimpaired controls, albeit on a protracted time scale, and indicated encoding of N1 during the PreN1 and N1 regions and N2 during the V and N2 regions (Fig. 1D). Stable performance was observed across measures for passive sentences within the two pre-treatment sessions, as well as the two post-treatment sessions.
Conclusion. These findings indicate that treatment supports re-learning of both offline and online sentence production, with the latter reflecting changes in cognitive strategies used to produce sentences. The emergence of normal-like sentence production processes in individuals with aphasia suggests that, rather than teaching compensatory strategies, treatment enhances access to normal processing routines. Post-treatment eye movements indicated relatively successful thematic mapping and encoding of sentence constituents. However, they were also suggestive of reduced incrementality as compared to unimpaired speakers (i.e., N2 was not encoded until production of N1 was complete), indicating residual deficits in sentence production planning. These results indicate that eyetracking is well-suited to detect change in sentence processes over time (cf. Mack & Thompson, submitted).
Cho, S., & Thompson, C. K. (2010). What goes wrong during passive sentence production in agrammatic aphasia: An eyetracking study. Aphasiology, 24(12), 1576-1592.
Lee, J., Yoshida, M., & Thompson, C. K. (2015). Grammatical planning units during real-time sentence production in agrammatic aphasia and healthy speakers. Journal of Speech, Language, and Hearing Research, 58, 1182-1194.
Mack, J. E., & Thompson, C. K. (submitted). Recovery of online sentence processing in aphasia: Eye movement changes resulting from Treatment of Underlying Forms.
Thompson, C. K., & Shapiro, L. (2005). Treating agrammatic aphasia within a linguistic framework: Treatment of Underlying Forms. Aphasiology, 19(10-11), 1021-1036.