A Foraging Approach to Analyzing Infant and Caregiver Vocal Behavior

Previous research on infant vocal development suggests that human infants and adult caregivers search for sounds that have social value. We hypothesized that this could be a foraging process in a high-dimensional acoustic space where the resources are adapting to the forager’s behavior. We studied day-long recordings of vocalizations in a naturalistic setting over the infants’ first year. We examined inter-vocalization time intervals and distance steps in an acoustic space defined by mean pitch and mean amplitude. Infant inter-vocalization intervals were shorter immediately following a vocal response from an adult. Adult intervals were shorter following an infant response and adult inter-vocalization pitch differences were smaller following the receipt of a vocal response from the infant. These findings are consistent with the hypothesis that infants forage vocally for social input. Increasing infant age was associated with changes in adult and infant inter-vocalization step sizes. The study represents a novel application of foraging theory to characterize infant-caregiver vocal interactions by assessing vocal exploration in terms of patterns of movement in acoustic space, which will allow this domain of behavior to be compared to other foraging behaviors.