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Current Evidence for the Existence of Laryngeal Macrotremor and Microtremor

NCJ Number
Polygraph Volume: 31 Issue: 2 Dated: 2002 Pages: 108-113
Thomas Shipp; Krzysztof Izdebski
Deedra Senter
Date Published
6 pages
In this study, two experiments were conducted to compare and contrast acoustic measures derived from the sustained vocalization of singers, patients with vocal tremor, and a normal non-singer. Electrical activity from limb and several laryngeal muscles during isometric contraction to define the characteristics of tremor when present in the voice and determine the presence or absence of small rhythmic contractions in sampled limb and laryngeal muscles was studied.
The notoriety surrounding the use of instruments designated as stress evaluators report that the presence or absence of laryngeal tremor in the voice is the basis for the determination of deception. This study set out to test the existence of laryngeal “microtremors” by conducting two experiments on humans. The attempt was to determine the presence or absence of small, rhythmic contractions in sampled limb and laryngeal muscles. The first portion of the study focused on specifying the rate, amplitude, and regularity of vocal vibrato in singers, a behavior caused by normal muscle contraction oscillations. Each subject was tape recorded while sustaining vocalization on vowel (a) for 7 to 12 seconds at various pitches. Pathologic subjects with a vocal disorder, spastic dysphonia, and a primary symptom of a strangled voice had an accompanying pronounced vocal tremor. They were recorded sustaining the vowel (a) for as long as possible at various pitches. In both groups acoustic oscillations between 4 and 8 Hz were found. The second portion of the study used a normal subject to sample electromvographic (EMG) activity from laryngeal and arm muscles during isometric contraction. The aim was to determine if a periodic component or microtremor was present. Results indicated that the rate of vocal vibrato in singers and of vocal tremor were consistent with values generated in other studies of these parameters. The experiments demonstrated that laryngeal muscles could oscillate at rates between 4 and 7 HZ to produce frequency changes associated with vocal vibrato. Due to the failure to find physiologic evidence of normal tremor in sampled laryngeal muscles, doubts were cast on the assumption made by manufacturers of stress analysis instruments that they detect the presence of laryngeal muscle tremor. References