The relationship between syntactic development and Theory of Mind: Evidence from a small-population study of a developmental language disorder

We investigated whether performance on false belief understanding tasks is related to language ability by looking at Russian-speaking children enrolled in a study of a developmental language disorder in a geographically isolated small population characterized by a high prevalence of developmental language disorders. All consenting children between the ages of 6 and 12 (n = 54) were given the Assessment of the Development of Russian Language (ORRIA), non-verbal IQ, short-term memory measures, a narrative task, and the Unexpected Transfer task of false belief. We found that language development scores were related to success on the false belief task even when controlled for IQ and short-term memory. Also, the group who succeeded on the false belief task had significantly higher syntactic complexity scores for narratives than those who failed it. References to mental states, manifested by the children’s use of mental, psychological and perception verbs, were not related to performance on the false belief task. These findings support the hypothesis that developed representations of false belief are tied to syntactic development, not general cognitive functioning or the acquisition of mental-state verbs.

► Developmental Language Disorder (DLD) appears to be associated with a significant delay in false-belief (FB) reasoning acquisition. In contrast to typically developing children, children with DLD become accurate on a FB reasoning task between the ages of 8 and 10.
► In addition to age, the only other factor that distinguished the fail- versus pass-FB groups was their general language ability as measured by the standardized scores on the Russian Oral Language assessment.
► Neither the children's general cognitive functioning nor their short-term memory (including the working component) was related to FB reasoning.
► The level of complex syntax development, but not the lexicon of mental and psychological terms was predictive of children's FB success.