Ultrasound tongue imaging of vowel spaces across pitches in singing

One important technique in singing is vowel modification: the adjustment of the resonance space based on the sung pitch for more efficient voice production. We explore whether vowel modification is a learned technique for enhanced acoustics, or if it is a necessary articulatory adjustment for high pitch production. 16 participants without vocal training participated in a singing experiment with ultrasound tongue imaging. Participants were asked to sing sets of English vowels across their comfortable pitch range rising by semitone in a steady tempo, resembling a vocal warm up exercise. Participants sang 5 sets of vowels in total, each set consists of 5 target vowels (i, ɛ, æ, ɑ, u) in randomized order with 1 filler (ɔ) closing each breath group. Images of tongue position were splined using DeepLabCut. Preliminary results show that untrained singers tend not to adjust their tongue positions by pitch, though cases of tongue lowering occasionally occurred, particularly for the participants who sing a wide pitch range. In contrast, additional pilot data from 2 trained operatic singers showed gradual tongue adjustments across their pitch range, neutralizing vowel contrasts at their highest pitches. We discuss findings with respect to vowel-pitch interaction, drawing implications on theories of voice production.