Theory of mind impairment in right hemisphere damage: A review of the evidence.

Among the hypothesized causes of communication impairments in people with damage to the right cerebral hemisphere (RHD) is an underlying impairment in Theory of Mind (ToM) (the ability to make inferences about other peoples' mental states). In this review, evidence is considered for a ToM impairment in adults with RHD by approaching the issue from two directions. First, indirect evidence for impairment of ToM is reviewed by looking at studies on the effects of RHD on the comprehension of indirect requests, that is, requests in which the speaker's wishes are not explicitly stated but must be inferred by the listener. Second, studies that directly investigate the effects of RHD on performance on tasks intended to tap ToM are reviewed. On the basis of the papers reviewed here, it is concluded that although people with RHD do show impairments on a variety of tasks that are thought to involve ToM cognition, evidence for a specific ToM impairment is still inconclusive. It is recommended that future studies take care to distinguish individual differences in participants' linguistic production and lesion location, that more care is taken to control for task difficulty, and that well-controlled studies are combined with more naturalistic, ecologically valid tasks.