Acoustic Structures Crying of Infants From 1 to 4 Months and Their Signification

Crying is a survival mechanism for babies and their almost exclusive means of expression until the age of 4 months. Babies 'cry is mostly related to pain, a feeling of hunger, discomfort or separation following the departure of a parent around. Crying is a complex but essential means of communication and information between a baby and his parents that raises the question of their meaning. The cry phenomenon consists of complex acoustic signals produced by the vocal cords and filtered by the vocal tract. The vibrations frequency determines the fundamental frequency, itself responsible for the perception of the cry tone (pitch). The frequency spectrum of a cry is modified during the passage through the upper airways forming broad bands called "resonance frequency" or "formants". From the specificity of a crying sequence, it is possible to extract dynamic information and relate it to the perception that the adult has of it. Thus dynamic crying is often perceived by the adult as an imminent need of the baby. Some studies have shown that a child's crying may change according to his degree of discomfort, suggesting that crying was a "graduated signal" whose frequency and timbre could vary along a continuum. These changes would explain why adult listeners would be able to dissociate crying babies of different intensities. Conversely, an inappropriate response to crying could gradually generate disorders of the relationship between the baby and the parent. However, despite their potential neuro-ethological interest, knowledge of information transmitted by babies's cry remains superficial. This could be related to the relatively obsolete techniques of recording or due to the lack of objective physiological data on babies 'cry. Finally, the perception and reactions of adults when they hear crying babies are not fully understood.