Adjustment of Vocal Tract Shape via Biofeedback: Influence on Vowels.

The study assessed 30 nonprofessional singers to evaluate the effects of vocal tract shape adjustment via increased resonance toward an externally applied sinusoidal frequency of 900 Hz without phonation. The amplification of the sound wave was used as biofeedback signal and the intensity and the formant position of the basic vowels /a/, /e/, /i/, /o/, and /u/ were compared before and after a vocal tract adjustment period. After the adjustment period, the intensities for all vowels increased and the measured changes correlated with the participants' self-perception.The diferences between the second formant position of the vowels and the applied frequency influences the changes in amplitude and in formant frequencies. The most significant changes in formant frequency occurred with vowels that did not include a formant frequency of 900 Hz, while the increase in amplitude was the strongest for vowels with a formant frequency of about 900 Hz.