Theory of mind in children with 'lesser variants' of autism: a longitudinal study

Background: The study investigated the development of theory-of-mind (ToM) knowledge in children with 'lesser variants' of autism (PDD-NOS) over a period thought to be critical for ToM development (i.e., 3 to 5 years of age). Method: The sample included 11 children with PDD-NOS; 23 normally developing children were included for cross-sectional comparison and 13 normally developing children for longitudinal comparison. The groups were comparable in verbal and non-verbal mental age. Two storybooks were used for repeated assessment of various aspects of the children's theory of mind: emotion recognition, the distinction between physical and mental entities, prediction of behaviour and emotions on the basis of desires and prediction of behaviour and emotions on the basis of beliefs. Results: The results showed that the children with PDD-NOS had specific difficulties in understanding and predicting other people's emotions on the basis of situational cues, desires and beliefs. However, their ability to predict actions from beliefs and desires were relatively intact. Compared to the normally developing children, these children achieved lower levels of theory-of-mind knowledge, both at time of initial assessment and approximately 6 months later. Conclusions: The data suggest that the theory-of-mind development of children with PDD-NOS is both delayed and deviant. The growth pattern of theory-of-mind skills in children with PDD-NOS seemed to be qualitatively different from the growth pattern found in the group of normally developing children