Objectives: The recommendation of a supine sleeping position led to a significant reduction of SIDS, but increased positional skull deformities (DP). Here, a quantitative analysis of babbling aims to complement previous studies of language-relevant competence based on items of the Bayley-scales that suggested the presence of developmental language delays in DP infants. Measures of fundamental frequency variability as proxies for vocal control are well suited for testing this assumption, since the laryngeal neuro-muscular system matures early and is coupled with brain function while working rapidly in coordinating the structures and mechanisms involved in infant sound production.
Methods: Sixty-six healthy, full-term infants with normal hearing and a monolingual background took part: (1) moderately asymmetrical DP group - N = 41; 21 male; (2) severely asymmetrical DP group - N = 10; 8 male; and (3) controls - N = 15; 5 male (group assignment based on stereophotogrammetric 360° scans). Fundamental frequency (fo) measures were taken as proxies for vocal control skills during babbling.
Results: A MANOVA revealed no significant multivariate effect for the shape group, Wilks' λ = 0.86, F(2, 63) = 1.21, p = 0.30, η2 = 0.07 (medium effect-size). The results do not support previous findings based on Bayley scale evaluations that suggested a negative impact of DP on language development during infancy.
Conclusions: A strong link between DP and brain dysfunction affecting vocal control, which would cause deviations in otherwise healthy DP infants, was not observed. Objective long-term studies of sound production are necessary to identify and/or understand the potential consequences of DP on early language development.
Keywords: Babbling; Deformational plagiocephaly; Fundamental frequency; Infant; Vocal control.
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