Neural encoding of infant-directed speech during infants' first year of life.

Infant-directed speech (IDS) is the speech register that adults use spontaneously in interactions with young infants. Compared to adult-directed speech (ADS), IDS is characterised by exaggerated prosody and acoustically exaggerated speech sounds, which have been proposed to facilitate early speech processing and subsequent language acquisition in young infants. This study investigated the neural basis of this processing advantage. Specifically, it assessed cortical tracking of the spectral information in IDS and ADS in infants at 4 and 9 months of age. In line with previous research, results showed more efficient cortical tracking of IDS than ADS. While overall cortical tracking efficiency increased with age, there was no significant register by age interaction, indicating that the processing benefit of IDS is not influenced by maturational or experiential factors. These findings suggest that IDS facilitates neural encoding of not only low-frequency prosodic information in the speech signal as suggested by previous studies, but also of finer-grained acoustic detail conveyed across frequencies in the speech spectrogram. Thus, by using IDS, caregivers provide their infants with an optimal speech signal for the challenging task of acquiring the prosodic and phonetic properties of their native language during their first year of life.