Scaling of glottal opening

Laryngeal control occurs mainly along two dimensions. One involves the longitudinal tension of the vocal folds and is used for control of fundamental frequency. The other involves abduction/adduction of the folds. This dimension is used in the vegetative functions of the larynx and in its phonetic function to control voicing and aspiration as well as voice quality. Although fine adjustments in timing of abduction/adduction gestures relative to supralaryngeal events produce contrasts of aspiration in obstruents, variations in the size of these gestures appear to be less significant and less finely controlled. The present experiment explores the control of laryngeal abduction/adduction by examining to what extent speakers can control size of glottal aperture under different conditions, with and without suitable feedback. The results suggest that voluntary control of the size of glottal opening is rather poor, and that subjects are unable to make very fine-graded adjustments along this dimension. Voluntary control of glottal opening in isolation is limited, perhaps because normal activities seldom require separate control of this variable. Instead, control of glottal opening is tightly couples to such other activities as respiration, swallowing and speech articulation. Even in the context of sound production, glottal aperture is poorly controlled, perhaps because the precise degree of opening (as opposed to precise timing of opening and closing) has comparatively little practical significance over a wide range of openings.