Abstract
This study assessed cortical tracking of temporal information in incoming natural speech in seven-month-old infants. Cortical tracking refers to the process by which neural activity follows the dynamic patterns of the speech input. In adults, it has been shown to involve attentional mechanisms and to facilitate effective speech encoding. However, in infants, cortical tracking or its effects on speech processing have not been investigated. This study measured cortical tracking of speech in infants and, given the involvement of attentional mechanisms in this process, cortical tracking of both infant-directed speech (IDS), which is highly attractive to infants, and the less captivating adult-directed speech (ADS), were compared. IDS is the speech register parents use when addressing young infants. In comparison to ADS, it is characterised by several acoustic qualities that capture infants’ attention to linguistic input and assist language learning. Seven-month-old infants’ cortical responses were recorded via electroencephalography as they listened to IDS or ADS recordings. Results showed stronger low-frequency cortical tracking of the speech envelope in IDS than in ADS. This suggests that IDS has a privileged status in facilitating successful cortical tracking of incoming speech which may, in turn, augment infants’ early speech processing and even later language development.
Highlights
Cortical tracking refers to the process by which cortical activity tracks dynamic patterns of incoming information, in this case speech input
This study provides the first evidence for neural tracking of naturally-produced continuous speech by preverbal infants
The temporal response function (TRF) approach is an effective method for quantifying cortical tracking of speech sounds using non-invasive EEG9, and one that is sensitive to the effects of selective attention and multisensory integration[9,38]
Summary
Cortical tracking refers to the process by which cortical activity tracks dynamic patterns of incoming information, in this case speech input. Selective attention[6,10,11,12] has been shown to play a significant role in facilitating cortical tracking as demonstrated when adults and school-aged children are presented with different strings of speech input to each ear and asked to switch their attention from one string to the other[3,6,10,11,12] In such studies, recordings of neural activity at the theta band (syllabic rate) using MEG show that neural activity is correlated with the acoustic amplitude envelope of both the attended and unattended streams, but that the patterns of correlation differ for both streams as a function of attention, with more accurate tracking recorded in response to the attended stream.
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