The Speech-To-Song Illusion Across Development and the Effects of High-Level Expectations

The typical listener can readily categorize auditory stimuli as either speech or song even though these structures share many acoustic similarities. These musical and linguistic categories may nevertheless take time to develop as children acquire language- and music-specific knowledge. In the Speech-to-Song (STS) illusion, multiple repetitions of a natural spoken utterance can give rise to a perceptual switch wherein the stimulus begins to sound song-like to the listener. While the STS illusion has been well-researched in adult listeners, it had yet to be investigated in children. In our study, we examined whether children experience the STS illusion by presenting participants across age groups (4 – 5, 6 – 7, 8 – 11, 18+ years) with speech excerpts known to elicit the STS illusion and asking them to rate the degree to which each of 10 consecutive repetitions sounds song-like. We also asked whether they would better detect pitch changes to stimuli that violate versus conform to Western key structure, an advantage that has been observed in prior work with adults which implicates a role for musical schematic knowledge in the STS illusion. Participants robustly experienced the STS illusion similarly at all ages. Younger children required more repetitions than adults to experience the STS illusion, and unlike for adults, it remains unclear whether they recruited Western musical knowledge on our pitch detect task. Individual differences in performance on musical and linguistic perceptual tasks did not correlate with STS measures, suggesting that the repetition-induced musical processing mode characteristic of the STS illusion may reflect a more general auditory phenomenon that is less dependent on explicit musical and linguistic skills. Overall, our findings suggest that the ability to experience distinct, domain-specific modes of listening for speech and song are present early in development, but the nature of this experience may change with age as music-specific processing mechanisms develop and become more refined by listening experience.