Age and language skills of deaf children in relation to theory of mind development.

Using four traditional false-belief tasks, I investigated deaf children's age and expressive language skills in relation to their theory of mind development. The children's parents who signed reported on their own knowledge of a mental sign vocabulary. The results indicate age of the child to be strongly related to theory of mind development. Deaf children demonstrated an ability to pass the theory of mind assessment battery between the ages of 7 and 8 years, on average. In comparison, hearing children have consistently demonstrated the ability to perform such tasks between the ages of 4 and 5 years. Therefore, the results indicate deaf children are delayed by approximately 3 years in this cognitive developmental milestone. Expressive language skills of the children and sign language skills of the parents who signed were not found to be significantly related to the children's theory of mind development.