Audiovisual speech perception deficits in unaffected siblings of children with developmental language disorder.

Siblings of children with developmental language disorder (DLD) often have weaker language skills compared to peers with typical development (TD). However, whether their language-relevant audiovisual skills are also atypical is unknown. Study 1 examined whether siblings use information about a talker's mouth shape during phonemic processing as children with TD do. Study 2 examined siblings' ability to match auditory words with observed word articulations. Only children with TD showed a significant MMN to audiovisual phonemic violations, suggesting that, just like in children with DLD, lip shape does not modulate phonemic processing in siblings. Children with DLD and siblings were also less accurate than children with TD at detecting audiovisual word mismatches. The N400 amplitude in children with TD was significantly larger than in children with DLD and marginally larger than in siblings. Phonemic and lexical representations in siblings lack audiovisual details, which may contribute to poor language development.