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CONCEPTS OF PHONATION 109
from the air tract; in man it is large, but degenerate in function." [418, p. 466] Hagara insists that the function of the epiglottis is confined to handling food and that when it is used in singing it blocks the larynx and stifles tone. [220, p. 23] In this opinion she is upheld by Shaw [518, p. 88] and Hemery. [238, p. 33] Evetts and Worthington report that amputation of the epiglottis causes no serious loss to the voice. [167, p. 3] Felderman also states that the epiglottis has no function in phonation. He offers as evidence the fact that "the finest specimens of song birds have no epiglottis." [173, p. 64]
THE VOCAL VIBRATO
The vocal vibrato is defined as a periodic oscillation of vocal tone above and below its normal pitch level, occurring at the rate of about 6.5 variations per second, and always within a semitone interval. It is not to be confused with a tremolo effect which usually varies more than a semitone [Tolmie 617] or with the vocal trill which is the rapid alternation of two distinct pitches in the interval of a semitone, whole tone or third. [Waters 647, p. 76; Henley 251] The vocal tremolo is defined as an irregular unsteadiness or faulty trembling of the pitch caused by interfering tensions, muscular weakness and the inability to maintain a stable adjustment of the laryngeal mechanism during phonation. [Wilcox 669, p. 39] In the trill a conscious regular musical interval is always maintained between two rapidly alternating tones. In the vibrato the concept of interval is entirely absent. [Seashore 511, p. 154]
The vibrato appears to be one factor in voice production that has undergone considerable experimental treatment. Of the 51 statements gathered on this subject, 16 are reports of experimental findings. An exhaustive summary of early research in this field is published in Volume III (1936) of the University of Iowa Studies in the Psychology of Music, edited by Carl E. Seashore. [511] Although the entire subject of vocal vibrato is still in its experimental stages, the reports of some of the investigators are informative and interesting to the teaching profession. Along with the physiological and acoustical data uncovered, there are also some speculations as to the causes and pedagogical treatment of the vibrato.
Westerman explains the vocal vibrato as a neuro-muscular phenomenon caused by the rate of discharge of action currents (nervous impulses) in the human body. By a physiological law, these impulses normally travel along the nervous system (e.g., from brain to muscle) with a frequency of from five to eight times per second. The vocal muscles, when normally activated during phonation, also receive their nervous energy |
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