Musical aptitude moderates ease and vividness but not frequency of the speech-to-song illusion.

Repetitions of a spoken phrase can induce a perceptual illusion in which speech transforms into song, known as the speech-to-song illusion. Speech acoustics that share certain pitch and timing properties with songs seem to be involved in facilitating the illusion, with a recent proposal suggesting that the illusion hinges on the individual ability to detect musical features latently present in speech. The current study tests this proposal by manipulating pitch and timing features of spoken phrases and examining how musical aptitude of listeners (specifically, their sensitivity to disruptions of musical melody and beat timing) moderates their experience of the illusion. The results show that the illusion is perceived by everyone regardless of their musical aptitude, with phrases that contain stable pitch and long periods of high sonority transforming more frequently. However, musical aptitude does moderate the speed and the strength of the illusion. Listeners with lower beat perception ability experience the illusion faster, which suggests involvement of temporal distortion processes during repetitions. Listeners with higher melody perception ability experience the illusion more strongly, which indicates involvement of musical pitch extraction rather than pitch distortion. These findings contribute new evidence on the complexity of an illusory experience in the auditory domain.