Nonlinear Phenomena in the Cries of Twin Infants: Relations to Emission Context and Genetic Influence

• Grant number: 25/12988-8
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: August 01, 2025
• End date: July 31, 2026
• Field of knowledge: Humanities - Psychology - Experimental Psychology
• Principal Investigator: Emma Otta
• Grantee: Tiago Cordeiro
• Host Institution: Instituto de Psicologia (IP). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 22/02107-6 - The University of São Paulo twin panel: research on twins' behavior, health, and well-being, AP.TEM

Abstract

The project is linked to the Thematic Project "USP Twin Panel: Research on Behavior, Health, and Well-being of Twins," FAPESP Process nº 2022/02107-6, and more specifically to Subproject P7, focused on the study of twin babies' cry. Human crying is one of the primary forms of communication between a baby and their caregiver (Zeifman, 2001). The phenomenon is adaptive and has a multifactorial origin, which can be studied from an ethological perspective (Lingle, Wyman, Kotrba, Teichroeb & Romanow, 2012). Within the scope of this research project, the twin study paradigm is well-established in the scientific literature for estimating the genetic contribution to the acquisition and development of behaviors (Nolan and Oh, 1996; Van Lierde, Vinck, De Ley, Clement & Van Cauwenberge, 2005). Among the behaviors that can be studied and benefit from this paradigm is the prosodic structure of crying (Wermke and Mende, 2009). Prosody consists of elements of language such as vocal intensity, voice quality, fundamental frequency (F0), and duration (Xu, 2011). This communicative feature can be seen in its early stages from infancy and can be observed in babbling and crying situations (Harold & Barlow, 2013). This research project also discusses possibilities for analyzing twin babies' crying through the study of nonlinear phenomena (NLPs) in the acoustic structure of these vocalizations, aiming to understand their characteristics and prevalence, and subsequently contribute to studies on child and twin development. Nonlinear Phenomena are defined as complex irregularities that do not require a fully developed and complex neural apparatus, which explains their presence from an early age in both human and non-human mammals (Fitch, Neubauer & Herzel, 2002). Studies indicate that NLPs evolved in mammals due to their ability to facilitate individual discrimination within the species, as well as to introduce unpredictability in vocalizations, which makes it harder for the infant's caregivers to ignore vocal signaling (Fitch et al., 2002). The objective of the present research project is to create a cataloged repository of recorded cries and analyze the melodic contour and sound quality, alongside the differences and prevalence of types and proportions of NLPs, relating them to chorionicity, zygosity, prematurity, and corrected age in twins aged 0 to 3 months. Therefore, the project aims to explore and discuss the genetic aspects influencing these vocalizations. (AU)