physiology of phonation

Laryngeal function for speech

Phonation, or voicing – the product of vibrating vocal folds

• Source of voice for speech

• Vocal folds vibrate as air passes through them (as they are approximated/adducted)

• Phonation is maintained by the Bernoulli effect and tissue elasticity - myoelastic aerodynamic theory

Attack stage (Vocal attack)

Begins at adduction

Sustained phonation

hold the VFs in fixed position in the airstream as the aerodynamics of phonation control the actual vibration (Myoelastic aerodynamic theory*)

Offset stage

Ends at abduction

Indication of inefficient phonation

• Incomplete closure

• Excess air escapes during vibration

• Excessive closure (hyperadduction)

• Too much resistance to airflow

Mucosal wave

the surface of the vocal folds moves in a wave-like (ripple) motion during vibration

Each vibration allows a brief puff of air to escape – repeated puffs create voicing (sound)

Fundamental Frequency

the rate of VF vibration

• Perceived as pitch

pitch

perception of fundamental frequency (F₀) – measured in Hertz (Hz)

Loudness

perception of intensity (amplitude) of the sound – measured in decibels (dB)

Mass (thickness of VFs)

Increase mass (thicker VFs) -> decrease frequency (pitch)

Tension

Increase tension -> increase frequency (pitch)

Length

Increase length (stretched) -> increase frequency (pitch)

Thyroarytenoid (TA)

can shorten and thicken the vocal folds, lowering pitch

Cricothyroid (CT)

can stretch and lengthen the vocal folds, increasing tension and raising pitch

increase loudness

• Vocal folds are brought together more firmly (adduction) – greater medial compression

• More pressure is needed to push air through the closed folds

greater subglottal pressure

loudness increases with

frequency

number of cycles per second

• Measured in Hertz (Hz)

• 1 Hz = 1 cycle per second

cycle

one complete opening and closing of the VFs

each one releases a small puff of air

breathy

• Incomplete closure

• Excess air escapes during vibration

strained

• Excessive closure (hyperadduction)

• Too much resistance to airflow