Melody complexity of infants' cry and non-cry vocalisations increases across the first six months

Abstract

In early infancy, melody provides the most salient prosodic element for language acquisition and there is huge evidence for infants' precocious aptitudes for musical and speech melody perception. Yet, a lack of knowledge remains with respect to melody patterns of infants' vocalisations. In a search for developmental regularities of cry and non-cry vocalisations and for building blocks of prosody (intonation) over the first 6 months of life, more than 67,500 melodies (fundamental frequency contours) of 277 healthy infants from monolingual German families were quantitatively analysed. Based on objective criteria, vocalisations with well-identifiable melodies were grouped into those exhibiting a simple (single-arc) or complex (multiple-arc) melody pattern. Longitudinal analysis using fractional polynomial multi-level mixed effects logistic regression models were applied to these patterns. A significant age (but not sex) dependent developmental pattern towards more complexity was demonstrated in both vocalisation types over the observation period. The theoretical concept of melody development (MD-Model) contends that melody complexification is an important building block on the path towards language. Recognition of this developmental process will considerably improve not only our understanding of early preparatory processes for language acquisition, but most importantly also allow for the creation of clinically robust risk markers for developmental language disorders.

Figure 1

(a–d) Melody (fundamental frequency—fo) contour diagrams (left) exemplifying simple (a: cry, b: non-cry) and complex (c: cry, d: non-cry) patterns together with the corresponding frequency spectra (time representation above) of the sounds (up to 4 kHz). The frequency scale of the melody diagrams is logarithmic, and the diagram grid marks semitone (fo) vs. time distances. Note that spectra a. and c. also display the inspiratory noise following the vocalisation. For the original audio files of these vocalisations see Supplementary Information.

Figure 2

Bubble plot of the proportion of complex melodies in cries over age together with the mean prediction line derived from the final multi-level mixed effects logistic regression model. Note: the bubble size gives the relative number. Here, the median bubble size represented n = 197, with Q1 = 88, Q3 = 331 and range: 2–1804.

Figure 3

Bubble plot of the proportion of complex melodies in non-cry vocalisations over age together with the mean prediction line derived from the final multi-level mixed effects logistic regression model. Note: the bubble size gives the relative number. Here, the median bubble size represented n = 102, with Q1 = 45, Q3 = 143 and range: 2–347.