Watching talking faces: The development of cortical representation of visual syllables in infancy

From birth, we perceive speech by hearing and seeing people talk. In adults cortical representations of visual speech are processed in the putative temporal visual speech area (TVSA), but it remains unknown how these representations develop. We measured infants' cortical responses to silent visual syllables and non-communicative mouth movements using functional Near-Infrared Spectroscopy. Our results indicate that cortical specialisation for visual speech may emerge during infancy. The putative TVSA was active to both visual syllables and gurning around 5 months of age, and more active to gurning than to visual syllables around 10 months of age. Multivariate pattern analysis classification of distinct cortical responses to visual speech and gurning was successful at 10, but not at 5 months of age. These findings imply that cortical representations of visual speech change between 5 and 10 months of age, showing that the putative TVSA is initially broadly tuned and becomes selective with age.

Automated summary

From birth, we learn speech by both hearing and seeing people talk. The cortical representations of visual speech in adults are processed in the temporal visual speech area (TVSA), but how these representations develop is unknown. In this study, we used functional Near-Infrared Spectroscopy to measure infants' cortical responses to silent visual syllables and mouth movements. Our results suggest that cortical specialization for visual speech may begin to emerge during infancy. The TVSA showed activity to both visual syllables and mouth movements at around 5 months of age, but exhibited more activity for mouth movements than visual syllables at around 10 months of age. Multivariate pattern analysis successfully classified distinct cortical responses to visual speech and mouth movements at 10 months, but not at 5 months. These findings indicate that cortical representations of visual speech change between 5 and 10 months of age, with the TVSA initially being broadly tuned and becoming more selective with age.