Infant magnetoencephalography studies exploring neural links between sensory and motor representations for speech.

Abstract

The adult brain exhibits anatomical and functional specialization specific to speech, but we have little information regarding the infant brain. Recent adult neuroimaging studies show that speech processing is left‐lateralized and that two regions of the brain, the superior temporal (ST, auditory area) and inferior parietal (IF, motor area), contribute to the brain’s response to speech. To explore brain activation to speech and nonspeech in infants, we used magnetoencephalography to image the whole brain. Experiment 1 examined infants at three ages: newborn, 6 months, and 12 months. Infants showed significant ST activation to both speech and nonspeech stimuli. IF activation was not observed in newborns but in the two older groups of infants we observed synchronous IF and ST activation that was unique to speech. Experiment 2 investigated the nature of this perceptual‐motor coupling for speech—specifically, we asked whether synchronous activation reflects the detection of speech signals per se, or whether it signals the recognition of experienced (native‐language) speech. Native, non‐native, and nonspeech analogs were used to test these alternatives. Our results elucidate the developmental time course of the sensory‐motor connections for speech, and address longstanding theoretical issues in speech perception.