Intact first- and second-order false belief reasoning in a patient with severely impaired grammar

Abstract

The retention of first-order theory of mind (ToM) despite severe loss of grammar has been reported in two patients with left hemisphere brain damage (Varley & Siegal, 2000; Varley, Siegal, & Want, 2001). We report a third, and more detailed, case study. Patient PH shows significant general language impairment, and severe grammatical impairment similar to that reported in previous studies. In addition we were able to show that PH's impairment extends to grammatical constructions most closely related to ToM in studies of children (embedded complement clauses and relative clauses). Despite this, PH performed almost perfectly on first-order false belief tasks and on a novel nonverbal second-order false belief task. PH was also successful on a novel test of “ToM semantics” that required evaluation of the certainty implied by different mental state terms. The data strongly suggest that grammar is not a necessary source of structure for explicit ToM reasoning in adults, but do not rule out a critical role for “ToM semantics.” In turn this suggests that the relationship observed between grammar and ToM in studies of children is the result of an exclusively developmental process.

Acknowledgments

The research reported in this paper was supported by grants from the Leverhulme Trust, the MRC and the Stroke Association.

We are very grateful to PH for his kind participation.

Notes

¹There is also an important literature demonstrating ToM abilities in nonverbal infants and non-human animals (e.g., Csibra, Gergely, Biro, Koos, & Brockbank, 1999; Emery, 2005; Onishi & Baillargeon, 2005). A discussion about the relationship between these abilities and those responsible for explicit reasoning using mental state concepts (beliefs, desires, intentions, etc.) is a crucial topic, but beyond the scope of the current article.

²Full details of the stimuli are available from the authors on request.