Activity of 37 cricothyroid motor units was studied' in three normal subjects. Single unit discharges were analysed during phonation at several different pitches, as well as in the absence of phonation. Interspike interval analyses were obtained, showing that frequency and variability of firing were dependent upon phonatory pitch. Interspike interval analyses from sequences obtained without accompanying phonation revealed preferred spike frequencies and limited variability. A U-shape function characterized the pitch-frequency relationship of a number of units. Postural adjustments were found to affect cricothyroid motor unit discharge. The technique described here using direct and continuous feedback of information to the subject offers a powerful tool for further analyses of laryngeal function.
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