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Abstract
Full-term neonates are capable of discriminating speech sounds and habituating to repeated auditory stimuli as soon as they are born. Differences in the electrophysiological waveform of neonates’ response is interpreted as an index of their ability to discriminate speech sounds. In addition, the decrement in response amplitude to a repeated stimulus reflects habituation. However, little research examines the relationship of these measures to each other in early infancy.
Event-related potential (ERPs) were recorded from 35 full-term neonates in response to two different test paradigms, consonant discrimination and habituation/novelty detection. In response to the consonant discrimination task, neonates significantly discriminated natural speech sounds with /b/-/g/ and /b/-/d/ contrasts. For the habituation task, trial-by-trial analysis demonstrated that neonates habituate to a repeated sound quickly, showing amplitude attenuation over the first ten experimental trials. At the introduction of a novel stimulus, neonatal electrophysiological response amplitude recovered, demonstrating novelty detection.
Individual differences in the electrophysiological response to these two paradigms were compared to assess the relationship between speech sound discrimination and habituation/novelty detection in the first few days of life. Habituation speed, speech sound discrimination, and response variability were estimated for each individual. A set of multilevel models indicated that each of these between-subjects predictors helped to describe the electrophysiological response to the novelty detection task. A model that includes all of these measures as predictors best characterized full-term neonatal electrophysiological responses. In addition, relationships between individual differences in speech sound discrimination, habituation, novelty detection, and response variability were described. Results indicated that some individual differences in the electrophysiological response map onto a general index of neonatal health / maturity. This research sheds light on the etiology of neonatal neurocognition and provides support for the validity of neonatal ERPs as predictive indicators of later development.
