Theory of mind in autism spectrum disorder: Does DSM classification predict development?

It is unclear how theory of mind (ToM; understanding mental states and their influence on behaviour) develops in autism spectrum disorders (ASD). At least two possibilities exist: development is delayed or developmental patterns deviate from normal. We used a cross-sectional design to examine ToM skills in 4-16 year-old children. First, participants were classified in terms of the DSM-IV categories low-functioning autism (n = 21), high-functioning autism (n = 24), Asperger's syndrome (n = 21), and pervasive developmental disorder not otherwise specified (PDD-NOS; n = 20). The high-functioning autism, Asperger's syndrome and PDD-NOS groups displayed delayed ToM onset compared to a typically developing group (n = 30), but normal ToM developmental rates and sequences; supporting delayed development. ToM in low-functioning ASD fit the deviant development model: Age did not predict ToM. A second ToM model using DSM-5 ASD and verbal IQ supported ToM development differences: Greater verbal ability was associated with increased ToM in ASD but not in typical development. As a single explanation for ToM development in ASD is insufficient, it is imperative to report specifiers such as intellectual functioning when using DSM-5 classification. DSM-IV classification contributed little to the prediction of ToM development beyond the influence of intellectual functioning.