Language facility and theory of mind development in deaf children.

Deaf children with signing parents, nonnative signing deaf children, children from a hearing impaired unit (HIU), and oral deaf children were tested on three first-order theory of mind (ToM) tasks--a subset was also given a second-order task (Perner & Wimmer, 1985). A British Sign Language (BSL) receptive language task (Herman, Holmes, & Woll, 1999) and four nonverbal executive function tasks were also administered. The new BSL task allowed, for the first time, the receptive language abilities of deaf children to be measured alongside ToM abilities. Hearing children acted as controls. These children were given the same tasks, except the British Picture Vocabulary Scale was substituted for the BSL task. Language ability correlated positively and significantly with ToM ability, and age was correlated with language ability for both the deaf and hearing children. Age, however, underpinned the relationship between ToM and language for deaf children with signing parents and hearing children but not for nonnative signing, HIU, or oral deaf children. Executive function performance in deaf children was not related to ToM ability. A subset of hearing children, matched on age and language standard scores with signing deaf children, passed significantly more ToM tasks than the deaf children did. The findings are discussed with respect to the hypotheses proposed by Peterson and Siegal (1995, 2000) and Courtin (2000).