Date of Award


Publication Type

Doctoral Thesis

Degree Name




First Advisor

Joseph Casey


Differential Diagnosis, High Functioning Autism, Nonverbal Learning Disorder, Psychosocial Functioning, Social Competence, Social Functioning




The variant of autism spectrum disorder (ASD) in which there is no evidence of a comorbid intellectual disability (often informally referred to as high functioning autism [HFA]) and nonverbal learning disorder (NLD) are two clinical disorders associated with social difficulties. Whereas social functions have been studied extensively in ASD, relatively little research has investigated social functioning in NLD. As such, it is unclear whether the pattern and severity of social functioning difficulties is different between these disorders. Furthermore, it is often challenging to establish a differential diagnosis between these disorders, which is critical given the need for different treatment approaches. The present study aimed to investigate parents’ perceptions of social adjustment in these groups, as well as to identify reliable differences in pragmatic communication, social motivation, and other aspects of social functioning based on behaviour inventories and standardized direct observation of social behaviour. Twenty-two participants (10 in the NLD group and 12 in the HFA group) between the ages of 9 and 17 years were recruited from Southwestern Ontario. The results indicated that overall both groups are characterized by social difficulties, with those of children in the HFA group tending to be more severe. The mean scores of each group were elevated in the At-Risk range on the Behavioral Symptoms Index composite of the BASC-2, indicating some social adjustment difficulties in both groups. The Social Interaction Difference Index (SIDI) from the Children’s Communication Checklist-2 (CCC-2) and the Overall Total score from Module 3 of the Autism Diagnostic Observation Schedule-2 (ADOS-2) each significantly discriminated between the groups. The Reduced Contact and Social Interest subscale of the Children’s Social Behaviour Questionnaire Revised (CSBQR) did not significantly predict group membership, and both groups were reported to have low frequency of interacting with peers. The present findings provide preliminary support that children in both groups experience social adjustment difficulties, pragmatic language difficulties, as well as reduced social interest in others, and preliminary evidence regarding the clinical usefulness of the CCC-2 and the ADOS-2 in the context of establishing a differential diagnosis between HFA and NLD.