Physiology of Phonation PDF

Preview

Summary

physiology of phonation...

Description

10/17/20 CSD 213 Physiology of Phonation 





Non-Speech Laryngeal Function o Protective function is the most important biological role of the larynx o Prevents entrance of foreign objects into the trachea o Coughing  Forceful evacuation of respiratory passageway in response to irritant or foreign matter  An individual takes a deep inhalation through widely abducted vocal folds  Vocal folds tense and form a tight adduction  Larynx elevates and high pressure of force expiration blows vocal folds apart expelling irritant or foreign matter o Throat clearing  Clears respiratory tract of mucous o Abdominal fixation  Impounds air in thorax to stabilize the torso  Lifting, pushing, or pulling Acoustics o What is acoustics?  The branch of physics concerned with the properties of sound o Process of vibration determined by:  Elasticity- property of a material that causes it to return to its original shape after being displaced  Stiffness- strength of the forces within a given material that restore it to its original shape on being distended  Inertia- property of mass dictating that a body in motion tends to stay in motion o Terms to know  Periodic waveform- repeats itself in a predictable fashion  Cycle of vibration- one point in a vibratory patten to the same point again  Period- the time it takes to pass through one cycle of vibration  Frequency- how often something occurs  For sound- cycles per second  Cycles per second is measured in Hertz (Hz)  Perceived as pitch  Intensity- increased amplitude (higher and lower compared to median line) of waveform  Measured in decibels (dB)  Perceived as loudness The Bernoulli Effect o Vocal folds are masses that may be set into vibration











o Phonation is the product of vibrating vocal folds within the larynx (voicing) o Phonation is maintained by the Bernoulli effect and tissue elasticity o Bernoulli effect states- given a constant volume flow of air or fluid, at a point of constriction there will be a decrease in pressure perpendicular to the flow and an increase in velocity of the flow o During phonation:  Vocal folds are nearly approximated at the instant the air stream is released by the forces of exhalation  The air stream will have a constant velocity until it reaches the glottal constriction  Velocity will increase as the air passes through the constriction  The result is a negative pressure between the medial edges of the vocal folds, and they will literally be sucked toward one another Laryngeal Function for Speech o Vocal attack- movement of vocal folds into the airstream for the purpose of initiating phonation o Sustained phonation- vocal folds held in a fixed position in the airstream; maintenance of a laryngeal posture through tonic (sustained) contraction of muscles o Termination- abduction of vocal folds Types of Vocal Attack o Simultaneous vocal attack- airstream is released just as the vocal folds meet (healthy)  Coordinate adduction of vocal folds and onset of respiration o Breathy vocal attack- airstream is released before vocal fold adduction starts o Glottal attack- adduction of the vocal folds prior to the airflow  If hard glottal attack, then damage may occur to the vocal mechanism Termination of Phonation o Abduction of the vocal folds (move apart)  Moves the vocal folds apart and out of the air stream  Terminates phonation  We terminate phonation many times during running speech to accommodate voiced and voiceless speech sounds  Both abduction and adduction occur very rapidly (many times a second) Sustained Phonation o Purpose of sustained phonation- adduction and abduction for speech o Sustained phonation depends on:  Maintaining muscular contraction  Placing the vocal folds into the airflow and holding them there Vocal Registers o Mode of vibration- pattern of activity that the vocal folds undergo during a cycle of vibration



o Vocal register- perceptual vocal variations defined by differential modes of vibration of the vocal folds o Three major types of vocal registers:  Modal register or modal phonation  Used in daily conversation  Usually most efficient  Vocal folds open and close from inferior to superior  Two variations of modal phonation: o Pressed- medial compression is greatly increased  Stronger, louder phonation with a harsh or strident quality  Often leads to damage of the vocal folds o Breathy- inadequate vocal fold approximation with excessive airflow between the vocal folds in the closed phase  Breathiness itself will not damage the cords, but it is inefficient and wastes breath support  May signal the presence of a vocal pathologya mass on the folds that is preventing them from adducting  Individuals may try to compensate by pressing  Glottal fry (pulse register)  Low frequency  Voice rough and low in pitch  Low subglottal pressure  Tension of vocalis reduced  Flaccid and thick vocal folds  Currently popular register (very controversial)  Falsetto register  Vocal sounds perceived as much higher than normal range (especially in males)  Vocal folds lengthen and become very thin  Increased vocal fold tension  Vocal folds only make brief contact, and only at their anterior margin Other Non-Phonatory Sounds o Whistle register- not considered a mode of phonation but a product of turbulence on the edge of vocal fold  Folds are extremely tense  Glottis is very narrow  Female voice- higher than falsetto o Whispering- not a mode of phonation, because no voicing occurs  Vocal folds are partially adducted and tense, creating turbulence in the airstream  Strenuous  Can fatigue the folds













Pitch and Frequency o Pitch is the way humans perceive frequency  This is one important element in speech perception o Frequency- number of cycles of vibration per second (Hertz or Hz)  Pitch increases as frequency increases  Pitch decreases as frequency decreases Types of Pitch o Optimal pitch- most efficient pitch for an individual  Varies with gender and age  Females average 212 Hz, males 132 Hz due to tissue mass and length o Habitual pitch- frequency habitually used by a person  Ideally optimal pitch and habitual pitch would be the same  If not, the effort to sustain phonation causes vocal fatigue Pitch Change at Puberty o Rapid muscle development o Height and weight gain- laryngeal cartilages and muscles included o This is more dramatic in boys  During growth spurt, there are pitch breaks during phonation  This is the normal result of changing tissue Pitch Range o Pitch range- range of frequencies an individual can produce  The mechanism is flexible  On average, the range is about 2 octaves  Calculated as difference between lowest and highest frequencies  Reduced by pathology  Increased through vocal training Pitch Changing Mechanism o A pitch increase comes from stretching and tensing the vocal folds  Involves the cricothyroid and vocalis muscles  Depends on changeable elements of vocal folds  Changes in tension, length, and mass  When the cricothyroid muscle tenses, the thyroid cartilage tilts down, lengthening the folds  This spreads the folds’ mass over more area  The vocalis fine tunes the tension for various pitches Intensity and Intensity Change o Intensity is the physical measure of power or pressure ratios o Loudness is the way humans perceive vocal intensity o We increase vocal intensity of vibrating vocal folds by:  Increasing subglottal pressure  Increasing medial compression o You can feel yourself doing this is you pretend to prepare to yell across the room  Your lungs take in extra air and your glottis tightens





Clinical Considerations o The phonation mechanism is very sensitive to physical health of speaker  Effect of physical problems on speaker  Weak voice  Voice decreases in intensity  Pitch range reduced  Rough voice quality is cases of upper respiratory tract Aspects of Pitch and Intensity that Accompany Language o Suprasegmental aspects of communication  Parameters of speech that are above the segment  Pitch and intensity play significant roles in prosody  Prosody includes:  Pitch  Intonation  Loudness  Stress  Duration  Rhythm  Use prosody to express a variety of different meanings in speech...