Theory of Mind Development in Deaf and Hard-of-Hearing Individuals: A Systematic Review.

Theory of Mind (ToM) is a construct that includes a range of connected abilities linked to the understanding of others' mental states. During the last three decades, ToM development has been studied extensively in deaf and hard of hearing (DHH) individuals and performances compared to the typically hearing (TH) population. Given the advances in the early diagnosis of deafness, interventions, and hearing devices over this period, variations in task performance among DHH participants might have been reduced. The current systematic review aims to synthesize all studies of ToM in DHH individuals and answer the following question: Do DHH individuals (Population), compared to a control sample of TH and/or among themselves (Comparator), in an assessment of ToM (Intervention), have differentiated results (Outcome)? After a search of the literature, 97 papers were included. We found that, in general, TH participants outperformed their DHH peers in ToM measures; however, there was a wide range of results. Explanations for this variability included the quality of early interactions and early exposure to both signed and spoken language. The review also indicates that the understanding of false belief was the most studied component within ToM, while other components, such as understanding intention and irony, require further research. Implications of these findings for clinical practice are discussed.