The effect of face orientation on audiovisual speech integration in infancy: An electrophysiological study.

Humans pay special attention to faces and speech from birth, but the interplay of developmental processes leading to specialization is poorly understood. We investigated the effects of face orientation on audiovisual (AV) speech perception in two age groups of infants (younger: 5- to 6.5-month-olds; older: 9- to 10.5-month-olds) and adults. We recorded event-related potentials (ERP) in response to videos of upright and inverted faces producing /ba/ articulation dubbed with auditory syllables that were either matching /ba/ or mismatching /ga/ the mouth movement. We observed an increase in the amplitude of audiovisual mismatch response (AVMMR) to incongruent visual /ba/-auditory /ga/ syllable in comparison to other stimuli in younger infants, while the older group of infants did not show a similar response. AV mismatch response to inverted visual /ba/-auditory /ga/ stimulus relative to congruent stimuli was also detected in the right frontal areas in the younger group and the left and right frontal areas in adults. We show that face configuration affects the neural response to AV mismatch differently across all age groups. The novel finding of the AVMMR in response to inverted incongruent AV speech may potentially imply the featural face processing in younger infants and adults when processing inverted faces articulating incongruent speech. The lack of visible differential responses to upright and inverted incongruent stimuli obtained in the older group of infants suggests a likely functional cortical reorganization in the processing of AV speech.

Infant social interactions and brain development: A systematic review.

From birth, interactions with others are an integral part of a person's daily life. In infancy, social exchanges are thought to be critical for optimal brain development. This systematic review explores this association by drawing together infant studies that relate adult-infant behaviours - coded from their social interactions - to children's brain measures collected during a neuroimaging session in infancy, childhood, adolescence or adulthood. In total, we identified 55 studies that explored associations between infants' social interactions and neural measures. These studies show that several aspects of caregiver-infant behaviours are associated with, or predict, a variety of neural responses in infants, children and adolescents. The presence of both concurrent and long-term associations - some of which are first observed just a few months postnatally and extend into adulthood - open an important research avenue and motivate further longitudinal studies.