Developmental differences in the hemodynamic response to changes in lyrics and melodies by 4- and 12-month-old...

Songs and speech play central roles in early caretaker-infant communicative interactions, which are crucial for infants' cognitive, social, and emotional development. Compared to speech development, however, much less is known about how infants process songs or how songs affect their development. Lyrics and melody are two key components of songs, and much of the research on song processing has examined how the two components of the songs are processed. The current study focused on the roles of lyrics and melody in song perception, by examining developmental patterns and the ways in which lyrics and melody are processed in the infants' brains using near-infrared spectroscopy (NIRS). The results revealed that developmental changes occur in infants' processing of lyrics and melody in a similar timeline as perceptual reorganization, that is, from 4.5 and 12 months of age. We found that 4.5-month-olds showed a right hemispheric advantage in the processing of songs that underwent a change in either lyrics or melodies. Conversely, 12-month-olds showed significantly higher activation bilaterally when lyrics and melody changed at the same time. These results suggest that 4.5-month-olds processed songs in the same manner as music without lyrics. Moreover, 12-month-olds processed lyrics and melody in an interactive manner, a sign of a more mature processing method. These findings highlight the importance of investigating the independent development of music and language, and also considering the relationship between speech and song, lyrics and melody in song, and speech and music more broadly.