Severe Impairment in Grammar Does Not Preclude Theory of Mind

Abstract

Debates about the role of language in human thinking are increasingly prominent in the cognitive sciences. There are claims that certain forms of reasoning can only be performed through access to the resources of the language faculty. In particular, a component of social cognition involving the representation of the mental states of others ('theory of mind' reasoning) has been claimed necessarily to involve propositions of natural language. A recent case study reported a man (SA) with severe agrammatic aphasia who was unable to understand or produce language propositions in any modality of language use, but who was able to complete theory of mind tasks. We report a replication of this finding using a modified picture theory of mind task with a second patient (MR). Despite severe aphasia and impaired performance on a test of executive function, MR demonstrated retained theory of mind reasoning. These results reveal the functional autonomy of theory of mind from the capacity for propositional/grammatical language, and support its independence from executive function.