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ABSTRACT
Background: 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.
Disclosure statement
No potential conflict of interest was reported by the authors.
Notes
1. A similar picture emerged with a more lenient analysis in which we corrected each inappropriate use of a reference term when we coded the following items. Such analysis does not count a continuing error as another error, and hence yields better results from the non-corrected one. (In sentences like “The fishermen returned to shore and then he told him”, the use of the high-accessibility marker he is inappropriate because there were two fishermen and as a result the second expression, “him” is also unclear. However, because there were only two characters in each story, if the first referring expression was appropriate, a listener could infer the second referent according to the binding principles of syntax alone, indicating that him cannot refer to the same referent as he). Even using this lenient analysis, the aTOMic participants still produced significantly fewer felicitous referring expressions than the TOMer participants and controls (U = 63, p < 0.001; U = 61, p = 0.001, respectively).
2. The four filler items served to make the test slightly more varied. They matched the experimental items in that there were two sentences and the participant was required to choose the appropriate one, but here the options did not differ in the amount of information, but rather in their phrasing. These were not control non-TOM items, because they still required the participants to consider different points of view of the conversers.
3. In the training stage of this experiment, the experimenter said a noun, and the participant had to point to this noun in a picture. All the aTOMic participants performed flawlessly on this task, showing preserved ability to identify the words and their picture representation.
4. Notice that there are only two possible lexical readings of the letter “b” or “l” in the context they were presented—either “ba-” or “be-” (or “le-” “la-”), so the random chance of reading the proposition correctly is (theoretically) 50%.
5. Except for cases where there is shared knowledge of specific and unique entities like “the sun” or entities otherwise familiar to the interlocutors (“mother” and “my teacher”).
6. Counting together filler items presented in an earlier version and in the final test version, 15 of the aTOMic participants were presented with filler items that included a morphosyntactic violation in the use of definiteness. In these items, they had to identify the morphosyntactic violation and offer a correction. The aTOMic patients’ average score on these items was 94% correct. Their good performance on the morphosyntactic aspects of definiteness alongside their poor application of the discoursive aspects of definiteness may be taken as yet another demonstration of the same dissociation between knowledge that is dependent on and independent of TOM in another linguistic construct.