When Language Is Not Enough: How to Explain ToM Abilities of Individuals with Williams Syndrome and Down Syndrome

This study examines the link between language abilities and Theory of Mind (ToM) development in individuals with Williams Syndrome (WS) and Down Syndrome (DS). We compared the results of 16 participants with WS, aged 6.3 to 27.2 years (Mean = 15.9 years, SD = 6.8 years), to those of 16 participants with DS, aged 10.7 to 23.9 years (Mean = 16.8 years, SD = 3.6 years). Using the French version of the ToM test-Revised (ToM test-R), we assessed three levels of ToM development: prerequisites, first-order beliefs, and second-order beliefs. Language abilities were evaluated using the Isadyle French language assessment battery, focusing on word comprehension, word production, syntax comprehension and production, and emotional lexicon. The results showed that the WS group performed significantly better in overall ToM skills in the ToM test-R compared to the DS group. Moreover, language skills were significantly associated with ToM development in the WS group, but not in the DS group. These findings underscore the importance of language development, particularly syntax and emotional understanding, in ToM acquisition. Through the application of a cross-syndrome approach, this study provides insights into how each syndrome impacts ToM development and the role of language in this process.