Williams syndrome (WS) is a neurodevelopmental disease characterized by mild to moderate intellectual disability and an extremely heterogeneous cognitive profile. Research has outlined two main features of WS: an atypical social behavior associated with surprising language abilities, and a hyperacusis. The purpose of this project is to investigate the relationships between both these abilities, and particularly the role of the hyperacusis on language abilities. The hyperacusis would be crucial in developing language skills: the apparent strength in the verbal domain could rely on Phonological Short Term Memory (PSTM) more in individuals with WS than in typically developing individuals. In addition, the investigators will compare individuals with WS to individuals with Down syndrome (DS): DS is often associated to strong limitations in the PSTM with poor language abilities. To this end, the investigators will use a highly innovative approach including physiological assessments (EEG-NIRS protocol) and questionnaires. The performance of people with WS will be compared to those of participants with DS and TD participants of same DA and cognitive assessments.