I still hear a melody: investigating temporal dynamics of the Speech-to-Song Illusion

The Speech-to-Song Illusion (STS) refers to a dramatic shift in our perception of short speech fragments which, when repeatedly presented, may start to sound-like song. Anecdotally, once it is perceived as a song, it is difficult to unhear the melody of a speech fragment, and such temporal dynamics of the STS illusion has theoretical implications. The goal of the current study is to capture this temporal effect. In our experiment, speech fragments that initially did not elicit the STS illusion were manipulated to have increasingly stable F0 contours to strengthen the perceived 'song-likeness' of a fragment. Over the course of trials, the speech fragments with manipulated contours were repeatedly presented within blocks of decreasing, increasing, or random orders of F0 manipulations. Results showed that a presentation order where participants first heard the sentence with the maximum amount of F0 manipulations (decreasing condition) resulted in participants continuously giving higher overall song-like ratings than other presentation orders (increasing or random conditions). Our results thus capture the commonly reported phenomenon that it is hard to 'unhear' the illusion once a speech segment has been perceived as song.