The “tree‐pruning hypothesis” in bilingualism

Abstract

Background: The “tree‐pruning hypothesis” (TPH) suggests that syntactic deficits in agrammatic production are highly selective: most patients have impaired tense inflection while their agreement inflection is preserved. The TPH states that the split‐inflection tree is pruned at the tense node, which is why an obvious dissociation in performance exists between tense and agreement. Aims: This study aims to determine whether the TPH applies to a bilingual individual by examining whether a dissociation in performance exists between agreement and tense inflection in the bilingual speaker's two languages: German and Luxembourgish. We expect the pattern of grammatical impairment to support the validity of the TPH in German and Luxembourgish. Methods & Procedures: The participant examined in this study, AM, is a pre‐onset balanced German–Luxembourgish speaker with Broca's aphasia and moderate agrammatism. We used a verb completion and grammatical assessment task to examine whether a dissociation in performance existed between tense and agreement in both languages. Outcomes & Results: The results comply with the TPH. The agreement results produced by the participant were significantly better than the tense results in both German and Luxembourgish. Conclusions: The results show a clear dissociation in each language as predicted by the TPH. This confirms that the TPH can be applied to both German and Luxembourgish.