Phonation Physiology Phonation = series of openings and closings of the vocal folds Two phases 1.Prephonation phase: period during which VFs move from abducted to either adducted or partially adducted position. Prior to onset of phonation, folds are in the abducted position. Vocal fold approximation: folds approximate and pressure beneath folds builds. Velocity of air through the glottal constriction is raised sharply, and pressure drops. Extent to which v. folds are approximated call medial compression (force with which folds brought together), caused by action of adductor muscles.

2.Attack phase Vocal folds are adducted and go thru initial vibratory cycles. Initiation of phonation: –As folds begin to approximate, a critical closure value is reached. –VFs begin to vibrate before they have actually approximated. –Folds undergo a # of vibrations before they meet completely to obstruct the air stream. –As long as subglottal pressure is adequate, medial compression of folds will be overcome and they will be blown apart, releasing a puff of air into supraglottal area. –These air puffs are source of voicing. The elasticity of folds and Bernoulli effect causes folds to snap back to midline (myoelastic aerodynamic theory of VF vibration)

–Theories of VF vibration Myoelastic aerodynamic theory: Phonation made possible due to aerodynamic and tissue force of laryngeal muscles. –BERNOULLI EFFECT: as air pressure decreases, velocity increases »Air has a constant velocity until reaches constriction. Used to explain why airplanes rise in the air. Velocity will increase as air passes thru glottal opening. The result is negative pressure between the medial edges of folds and they are drawn toward each other. –Folds also approximate due to myoelastic properties. »Muscles adduct folds and apply tension or stiffness to folds »Viscous (elastic) force created by density of VF tissue »More viscous, more resistance to air flow. »Mechanical coupling stiffness = outermost layer of VFs functions as if composed of two different masses. Lower mass pulls upper mass away from midline when air pressure is great enough.

Three mass model of VF vibration –Problem with myoelastic aerodynamic theory: »Doesn’t explain how VFs sustain oscillation –This model adds the supraglottal area to the equation. »Air pressure from lungs always has to be positive »Air flows from positive to negative pressure locations »Air pressure has to be negative at the level of the glottis, but how is it created? »Supraglottal airflow continues outward, even during VF closure, creating negative pressure just above the folds »Air pressure is the driving force of sustained oscillation

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Characteristics of the Vibratory Cycle 1.Glottal area (at normal pitch and loudness levels) opening phase-around 50% of one cycle –Subglottic pressure? closing 37% of one cycle closed 13% –Subglottic pressure?

2. Mode of Vibration: (in modal register) A. Opening/closing: v. folds begin to open (normally) posteriorly, with chink moving anteriorly. Closure begins with entire medial edge moving toward midline. Posterior part last to close.

B. Vibration: At conv. pitch and intensity levels, v. folds vibrate almost in their entirety. C. Vertical phase difference: v. folds begin to be forced open from beneath or at bottom of closure. Lower edges first to be blown apart, upper edges last to be blown apart. During closing phase lower edges close first, then upper edges.

Important factors governing vocal fold vibration 1) vocal fold position - degree of adduction glottal adductors: a) lateral cricoarytenoid m b) transverse interarytenoid m. c) oblique interarytenoid 2) vocal fold myoelasticity - length + tension glottal tensors/relaxors: a) cricothyroid m. b) thyroarytenoid m. 3) “amount/size” of pressure drop along the folds

Fundamental Frequency Change 1.VF length At modal frequencies, as VF length increases, frequency increases. Seems to go again what happens with stringed instruments Reason for difference: the vibrating portion of the VFs decreases as frequency increases. 2.VF mass As mass increases, frequency decreases 3.VF tension As tension increases, so does frequency

Loudness Change Degree and timing of VF closure If VF closed time is increased, then there is more time to build up pressure beneath then. Louder sound occurs when subglottic air pressue is adequate enough to blow VFs apart (overcome the resistance). Resistance is the important factor for intensity. The more resistance there is, the more pressure is needed to overcome the resistance. Thus, when the resistance is overcome, the pressure disturbance is greater = louder