Acoustic and affective qualities of IDS in English

This study examines modifications to the acoustic and affective qualities of infant-direct speech (IDS) from birth to 12 months. The acoustic analysis of fundamental frequency shows that IDS has the highest level of mean fundamental frequency (F0) in speech to infants at 6 months, and the highest level of pitch range in speech to infants at 12 months. Sex-based differences were evident with mothers using higher mean-F0 and pitch range in speech to female than male infants. The mother’s speech samples were also rated on five scales of communicative intent. Two factors, labelled ‘Affective’ and ‘Attentional’, were extracted from these scales. Analysis of variance of the derived factor scores shows that mothers have the highest scores on the Affective factor at 6 and 12 months, while the maximum on the Attentional factor occurs at 9 months. Mothers also increase their use of both these IDS components more in speech to girls than boys.