Objective:
The physiological functions of the vocal ligament are not fully understood. One function is to limit mechanical strain (elongation) of the vocal folds, a general function of most ligaments in the body. A second function may be to produce a firm closure of the glottis by forming a straight edge along the membranous (vibrating) portion of the vocal fold. The study reported here aimed to train frequent production of very high fundamental frequencies, at a range where the vocal ligament is thought to play a significant role in determining vibration frequency, and to measure changes pitch range and quality as a result of this practice.

Methods:
27 volunteers were recruited to participate in an 8-week exercise regimen where participants were asked to spend 2 minutes, 5 times per day producing pitch glides above 400 Hz for lower voices and above 800 hz for higher voices. The daily practice was repeated at least 5 days per week for 8 weeks. Vowel shape and loudness were not controlled as the target behavior was simply the stretching and vibration of the vocal folds at the target frequencies. The participants’ maximum phonation frequency was recorded before and after participation in the 8-week protocol, along with recordings of maximum phonation time, the rainbow passage, and a spontaneous connected speech sample. Contact quotient was measured using an EGG during the maximum phonation time task.

Results:
Preliminary analysis indicates that more than half of participants demonstrated increases in maximum pitch, and increased contact quotient after participation. Changes in habitual pitch were inconsistent across subjects.

Conclusions:
This study provides some evidence that maximum phonation frequency and glottal closure are changeable with frequent stretching of the vocal ligament during vibration. While other explanations are possible, such as improved neuromotor control, it is plausible that these changes are a result of changes to the morphologic properties of the vocal ligament.