The developmental origins of voice processing in the human brain

Abstract

In human adults, voices are processed in specialized brain regions in superior temporal cortices. We examined the development of this cortical organization during infancy by using near-infrared spectroscopy. In experiment 1, 7-month-olds but not 4-month-olds showed increased responses in left and right superior temporal cortex to the human voice when compared to nonvocal sounds, suggesting that voice-sensitive brain systems emerge between 4 and 7 months of age. In experiment 2, 7-month-old infants listened to words spoken with neutral, happy, or angry prosody. Hearing emotional prosody resulted in increased responses in a voice-sensitive region in the right hemisphere. Moreover, a region in right inferior frontal cortex taken to serve evaluative functions in the adult brain showed particular sensitivity to happy prosody. The pattern of findings suggests that temporal regions specialize in processing voices very early in development and that, already in infancy, emotions differentially modulate voice processing in the right hemisphere.

Figure 1

Voice-Sensitive Brain Regions Identified in 7-Month-Old Infants in Experiment 1 This graph depicts mean oxygenated hemoglobin concentration changes (±SEM) for vocal and other sounds measured from 24 NIRS channels. Channels that showed significant increases for vocal compared to other sounds are marked in red on the head model.

Figure 2

Brain Responses in 4-Month-Old Infants in Experiment 1 This graph depicts mean oxygenated hemoglobin concentration changes (±SEM) for vocal and other sounds measured from 24 NIRS channels. The channel that showed a significant increase for other sounds compared to vocal sounds is marked in blue on the head model.

Figure 3

Brain Regions Modulated by Emotional Prosody in Experiment 2 This graph depicts mean oxygenated hemoglobin concentration changes (±SEM) for happy, angry, and neutral prosody measured from 24 NIRS channels. The channel that showed an increased sensitivity to angry prosody is marked in magenta, and the channel that showed increased sensitivity to happy prosody is marked in blue on the head model.