Relationship between theory of mind and language ability in children and adolescents with intellectual disability.

Abstract

The present study was designed to evaluate the validity of the false belief task as a measure of theory of mind development in individuals with intellectual disability (ID). In most if it variants, the false belief task is linguistically demanding. This raises the possibility that the finding that individuals with ID do poorly on it might reflect language difficulties rather than theory of mind difficulties. Complicating matters further, however, is the fact that there are theoretical reasons to suppose that there might be a relationship between some dimensions of language ability and theory of mind development in individuals with ID (as well as in other populations). In the present study, children and adolescents with ID and typically developing (non-verbal) mental age matches completed a standard false belief task and several tasks designed to measure language ability. We reasoned that a pattern in which false belief performance was correlated with all measures of language ability would reflect an artefactual relationship, whereas a more highly circumscribed, theoretically sensible pattern of correlations that was similar across both groups would support the validity of the false belief task. The results indicated that for individuals with ID who have limited narrative language skills, those limitations contribute substantially to their failure on the false belief task. For individuals with ID who have more highly developed narrative language skills (about 40% of the sample tested), however, the false belief task may provide a valid measure of their progress towards acquiring an adequate theory of mind. This latter conclusion was suggested by the fact screening out individuals who failed to meet linguistic and cognitive prerequisites for dealing with the performance demands of the false belief task yielded non-significant correlations between false belief performance and the language measures for both the group with ID and the typically developing comparison group.