The effect of theory of mind impairment on language: Referring after right-hemisphere damage

Abstract

ABSTRACTBackground: Some patients after right-hemisphere damage show difficulty in Theory of Mind (TOM) tasks, namely, in the ability to attribute and reason about mental states of others and of themselves.Aims: We explored how such TOM impairment (aTOMia) following brain damage affects language abilities that are related to TOM. Specifically, we explored the ability of individuals with aTOMia to use and comprehend various referring expressions (e.g., definite and indefinite noun phrases, proper names, and pronouns) according to the speaker’s assessment of the addressee’s knowledge state about the referent.Methods & Procedures: We compared linguistic abilities that depend on the evaluation of shared knowledge, and hence might be affected by TOM impairment, to purely syntactic tasks, unrelated to TOM. TOM-related abilities were assessed using 6 tasks that test the comprehension, production, and judgment of various types of referring expressions. Non-TOM, syntactic, abilities were assessed using 4 tasks of comprehension and production.The participants were 21 Hebrew speakers with right-hemisphere damage aged 25–65 years (mean 52;2), 6 women and 15 men. Twenty of them had a right cerebrovascular accident, and one patient was surgically treated for the removal of a tumour. Fourteen of them were aTOMic, whereas 7 showed normal TOM. We compared the TOM-dependent linguistic abilities of the aTOMic patients to the brain-damaged patients with normal TOM, and to an age-matched control group.Outcomes & Results: The participants with aTOMia performed consistently worse on the TOM-related linguistic tasks than the right-hemisphere-damaged participants with intact-TOM and the healthy control group. They failed to take into account the mental state of the interlocutors and the knowledge that they share in selecting a referring expression. In contrast, their syntactic abilities, which are not dependent on TOM, were intact. Their comprehension of relative clauses, Wh-questions, and object pronouns was normal, and their production of embedded sentences was similar to the controls. The aTOMic and non-aTOMic participants performed similarly to controls on the TOM-independent syntactic tasks.Conclusions: Individuals who have aTOMia following right-hemisphere damage might show specific impairments in language, when the comprehension and production require TOM. An important implication of this study is, thus, that although these individuals do not suffer damage to the language areas in the brain, they should be considered for language evaluation and treatment.