The development of multisensory speech perception continues into the late childhood years

Observing a speaker's articulations substantially improves the intelligibility of spoken speech, especially under noisy listening conditions. This multisensory integration of speech inputs is crucial to effective communication. Appropriate development of this ability has major implications for children in classroom and social settings, and deficits in it have been linked to a number of neurodevelopmental disorders, especially autism. It is clear from structural imaging studies that there is a prolonged maturational course within regions of the perisylvian cortex that persists into late childhood, and these regions have been firmly established as being crucial to speech and language functions. Given this protracted maturational timeframe, we reasoned that multisensory speech processing might well show a similarly protracted developmental course. Previous work in adults has shown that audiovisual enhancement in word recognition is most apparent within a restricted range of signal-to-noise ratios (SNRs). Here, we investigated when these properties emerge during childhood by testing multisensory speech recognition abilities in typically developing children aged between 5 and 14 years, and comparing them with those of adults. By parametrically varying SNRs, we found that children benefited significantly less from observing visual articulations, displaying considerably less audiovisual enhancement. The findings suggest that improvement in the ability to recognize speech-in-noise and in audiovisual integration during speech perception continues quite late into the childhood years. The implication is that a considerable amount of multisensory learning remains to be achieved during the later schooling years, and that explicit efforts to accommodate this learning may well be warranted.