Using naturalistic paradigms to study how adult speakers accommodate infant listeners’ unique processing demands

Abstract

Communication is inherently social and requires an efficient exchange of complex acoustic cues between individuals. What are the behavioral and neural processes that allow young listeners to understand, couple to, and learn from adult speakers in complex, everyday interactions? In one study, we recorded mothers’ natural speech during play and reading and uncovered a pervasive timbre fingerprint of infant-directed speech (IDS) that generalized across 10 diverse languages. Classification of IDS and adult-directed speech (ADS) was driven by a statistical summary measure that concisely describes the vocal spectrum and could not be explained by pitch alone. In a second study, using dual-brain functional near-infrared spectroscopy (fNIRS), we measured the real-time neural dynamics of communication between infants and adults during natural interaction. We found that the infant prefrontal cortex (PFC) tracked several communicative cues, including the adult’s pitch variability, with high temporal precision. Furthermore, infant-adult neural coupling was significantly greater when the members of a dyad interacted with each other than when they performed control tasks. Surprisingly, PFC activation in the infant brain slightly preceded similar activation in the adult brain, which crucially advances our understanding of children’s influence over the accommodative behaviors of the caregivers around them during everyday communication.