Assessing Theory of Mind Nonverbally in Those With Intellectual Disability and ASD: The Penny Hiding Game

Individuals with autism spectrum disorder (ASD) and low intellectual/language abilities are often omitted from experimental studies because of the challenges of testing these individuals. It is vital to develop appropriate and accessible tasks so that this significant part of the spectrum is not neglected. The theory of mind (ToM) has been extensively assessed in ASD, predominantly in relatively high-functioning individuals with reasonable language skills. This study aims to assess the ToM abilities of a sample of 132 participants with intellectual disability (ID) with and without ASD, matched in verbal mental age (VMA) and chronological age, using a naturalistic and nonverbal deception task: the Penny Hiding Game (PHG). The relationship between performance on the PHG and everyday adaptation was also studied. The PHG proved accessible to most participants, suggesting its suitability for use with individuals with low cognitive skills, attentional problems, and limited language. The ASD + ID group showed significantly more PHG errors, and fewer tricks, than the ID group. PHG performance correlated with Vineland adaptation scores for both groups. VMA was a major predictor of passing the task in both groups, and participants with ASD + ID required, on average, 2 years higher VMA than those with ID only, to achieve the same level of PHG success. VMA moderated the association between PHG performance and real-life social skills for the ASD + ID more than the ID group, suggesting that severely impaired individuals with ASD may rely on verbal ability to overcome their social difficulties, whereas individuals with ID alone may use more intuitive social understanding both in the PHG and everyday situations.