Newborns' Cries are Unique to Individuals (But Not to Language Environment)

Acoustic developmental programming: a mechanistic and evolutionary framework

Conditions experienced prenatally, by modulating developmental processes, have lifelong effects on individual phenotypes and fitness, ultimately influencing population dynamics. In addition to maternal biochemical cues, prenatal sound is emerging as a potent alternative source of information to direct embryonic development. Recent evidence suggests that prenatal acoustic signals can program individual phenotypes for predicted postnatal environmental conditions, which improves fitness. Across taxonomic groups, embryos have now been shown to have immediate adaptive responses to external sounds and vibrations, and direct developmental effects of sound and noise are increasingly found. Establishing the full developmental, ecological, and evolutionary impact of early soundscapes will reveal how embryos interact with the external world, and potentially transform our understanding of developmental plasticity and adaptation to changing environments.

Individual differences in infancy research: Letting the baby stand out from the crowd

Within the developmental literature, there is an often unspoken tension between studies that aim to capture broad scale, fairly universal nomothetic traits, and studies that focus on mechanisms and trajectories that are idiographic and bounded to some extent by systematic individual differences. The suitability of these approaches varies as a function of the specific research interests at hand. Although the approaches are interdependent, they have often proceeded as parallel research traditions. The current review notes some of the historical and empirical bases for this divide and suggests that each tradition would benefit from incorporating both methodological approaches to iteratively examine universal (nomothetic) phenomena and the individual differences (idiographic) factors that lead to variation in development. This work may help isolate underlying causal mechanisms, better understand current functioning, and predict long-term developmental consequences. In doing so, we also highlight empirical and structural issues that need to be addressed to support this integration.

Affective reactivity to cry sounds predicts young women's reactivity and behavior in a simulated caregiving task

Different populations of adults (experienced vs. inexperienced caregivers, men vs. women, abusive vs. nonabusive parents, etc.) have been reported to differ in their affective reactions to the sounds of infant crying. These differences are thought to impact caregiving behavior and, in some instances, to affect long-term outcomes for infants. There can be great intra-group variation, however, even when group differences are significant; modeling developmental process will require a finer grained approach. We have undertaken a pair of studies intended to validate the Negative Affect Scale (NA) from the PANAS as a measure of individuals' affective reactivity to cry sounds. In Study 1, 306 young women who were not yet mothers listened either to infant crying or to birdsong. The results supported the NA as a measure of reactivity to crying. In Study 2, a new sample of 301 young women listened to crying in a screening task; a group of "high reactors" (n = 21) and a group of "low reactors" (n = 22) then participated in a simulated caregiving situation. Individuals' affective reactivity to the caregiving simulation mirrored their affective reactivity in the screening task, and rates and overall organization of caregiving behavior differed between the groups. Changes in negative affect, then, appear to be both a result of infant crying and a determinant of some aspects of caregiving behavior. Further studies will extend these laboratory results to real infants and their caregivers, and further validate the NA as a measure of individual differences in reactivity to cry sounds.