PHONATION.pptx

Phonation-the production of vocal sounds and especially speech.
The term phonation has slightly different meanings depending on the subfield of phonetics( i.e., the studies of how human produce and perceive sounds).
Among some phoneticians those who studies laryngeal anatomy and physiology and speech production, phonation is the process by which the vocal folds produce certain sounds through quasiperiodic vibration.
Laver (1994:184) defines phonation as the use of the laryngeal system to generate an audible source of acoustic energy (the source in the sense of the source-filter model of speech production) which can then be modified by the articulatory actions of the rest of the vocal apparatus (the filter in the source-filter model).
According to phoneticians in other subfields of phonetics , phonation refers to any oscillatory state of any part of the larynx that modifies the airstream, of which voicing is an example.

Phonation is the status of vocal folds while air (the initiatory airstream) passes through the glottis, as in:
Wide open glottis – relaxed vocal folds
Narrowing of glottis – vibrating vocal folds
When air is forced into a narrow tube, that volume of air has to squeeze into a smaller space. The vocal folds are made up of muscle and epithelial tissue. What you hear as voicing is the product of the repeated opening and closing of the vocal folds. The act of bringing the vocal folds together for phonation is adduction, and the process of drawing the vocal folds apart to terminate phonation is abduction. Phonation, or voicing, is the product of vibrating vocal cords in the larynx.

1. PHONATION anatomy, types, physiology and mechanism UDAY DUTTA

2. Definition: Phonation-the production of vocal sounds and especially speech. The term phonation has slightly different meanings depending on the subfield of phonetics( i.e., the studies of how human produce and perceive sounds). Among some phoneticians those who studies laryngeal anatomy and physiology and speech production, phonation is the process by which the vocal folds produce certain sounds through quasiperiodic vibration. Laver (1994:184) defines phonation as the use of the laryngeal system to generate an audible source of acoustic energy (the source in the sense of the source-filter model of speech production) which can then be modified by the articulatory actions of the rest of the vocal apparatus (the filter in the source-filter model). According to phoneticians in other subfields of phonetics , phonation refers to any oscillatory state of any part of the larynx that modifies the airstream, of which voicing is an example. Phonation is the status of vocal folds while air (the initiatory airstream) passes through the glottis, as in: Wide open glottis – relaxed vocal folds Narrowing of glottis – vibrating vocal folds When air is forced into a narrow tube, that volume of air has to squeeze into a smaller space. The vocal folds are made up of muscle and epithelial tissue. What you hear as voicing is the product of the repeated opening and closing of the vocal folds. The act of bringing the vocal folds together for phonation is adduction , and the process of drawing the vocal folds apart to terminate phonation is abduction . Phonation, or voicing, is the product of vibrating vocal cords in the larynx.

3. Anatomy of Phonation: Anatomical structures involved in phonation- A n airstream in the lungs passes into the trachea and finally into the larynx , creating a pressure drop across the larynx. When the pressure drop become sufficiently large ,the vocal folds start to oscillate , the oscillating vocal fold are responsible for activating vibration of air which produces a glottal tone latter modified in the cavities of vocal tract.  The larynx is the principal structure for producing vibrations of the air stream as well as production of sound. During phonation, the vocal folds act as an energy transducer that converts aerodynamic power, generated by the chest, diaphragm, and abdominal musculature, into acoustic power radiated at the lips that is heard as voice. The energy transduction that is key to this process occurs primarily at the glottis, in the aperture between the vocal folds, but is influenced by both subglottal and supraglottal variables.

4. Larynx (commonly called the voice box) - Musculo-cartilaginous structure located at the superior end of the trachea ,comprised of three unpaired cartilages(cricoid ,thyroid ,and epiglottis) and three paired cartilages (arytenoid ,corniculate ,cuneiform) bound by ligaments ,lined by mucous membrane and supported by numerous muscles from the hyoid bone which enable it to move up and down. Laryngeal cartilages- there are nine cartilages; Unpaired cartilages: thyroid cartilage, cricoid cartilage, epiglottis, Paired cartilages: arytenoid cartilages, corniculate cartilages, cuneiform cartilages,

5. Laryngeal membrane ligaments- The laryngeal membranes and ligaments support the  cartilaginous skeleton  of the larynx . Extrinsic ligaments: thyrohyoid membrane and ligaments lateral thyrohyoid ligament median thyrohyoid ligament hyo-epiglottic ligament cricotracheal ligament Intrinsic ligaments: cricothyroid ligament quadrangular membrane vestibular ligament cricovocal membrane Vocal ligament The arytenoid cartilages have vocal process to provide the sites of attachment for the vocal ligament, thereby permitting opening and closing movement of the vocal folds in phonation. Thus the larynx plays an important role in phonation in speech.

6. Fig- Laryngeal cartilages and ligaments

7. Laryngeal muscles- there are two group of laryngeal muscles responsible for sound production. Extrinsic muscles: which produce the movement of hyoid bone at the time of vocalization and swallowing. That consist of- suprahyoid muscles(stylohyoid ,digastric ,mylohyoid ,geniohyoid)elevate the hyoid bone , infrahyoid muscles(sternohyoid ,omohyoid ,sternothyroid ,thyrohyoid) depress the hyoid bone. Intrinsic muscles: which move the vocal cartilages and control tension in order to produce speech sounds. The are functionally divided into- adductors(lateral cricoarytenoid, transverse arytenoid) , abductors(posterior cricoarytenoid) , sphincters(transverse arytenoid ,oblique arytenoid ,aryepiglottic) , muscles that tense the vocal cord(cricothyroid) , muscles that relax the vocal cords(thyroarytenoid ,vocalis).

8. Fig – Laryngeal (extrinsic and intrinsic) muscles

9. Laryngeal folds- there are two soft tissue folds located with in the larynx- the vestibular folds and vocal folds(play a crucial role in phonation). Vocal folds/Vocal cord: the vocal folds are located within the larynx at the top of the trachea. They are attached posteriorly to the arytenoid cartilages, and anteriorly to the thyroid cartilages. They are part of the glottis. Vestibular folds/Ventricular folds/False vocal fold: these are a pair of thick folds of mucous membrane that protect and sit slightly superior to the more delicate true folds. They have a minimal role in normal phonation, but are often used to produce deep sonorous tones in Tibetan chant as well as in musical screaming. Laryngeal cavity- extends from laryngeal inlet to lower border of the cricoid cartilages , narrow in the region of vestibular folds( rima vestibuli) and narrowest in the region og vocal folds( rima glottidis)divided into three parts; Supraglottic part/Vestibule- part between the vestibular folds, Ventricle- part between the vestibular and vocal folds, Infraglottic part- part between the vocal folds.

10. Fig- Laryngeal folds Fig- Laryngeal cavity

11. Different types of phonation: Peter Ladefoged suggested that there might be a continuum of phonation types, defined in terms of the aperture between the arytenoid cartilages, ranging from voiceless (furthest apart), through breathy voiced, to regular, modal voicing, and then on through creaky voice to glottal closure (closest together). This continuum is depicted schematically in figure below- Fig- Continuum of phonation types (after Ladefoged 1971)   Cross-linguistic investigation suggests that this phonation continuum can be defined in terms of a recurring set of articulatory, acoustic, and timing properties. Nevertheless, there exist several languages whose phonation contrasts do not neatly fall within the phonation categories defined by other languages . Different types of phonation occurs due to different states of vocal folds ,supraglottal structures and overall larynx during airflow ,Such as- abduction and adduction of vocal folds; constriction of supraglottal structures; adjustment of length, stiffness and thickness of the vocal folds; elevation and lowering of the larynx.

12. The tension and adjustment forces acting on the vocal folds are - The active longitudinal tension of the vocal folds is achieved through the contraction of the vocalis muscle, whereas the passive longitudinal tension is achieved through contraction of the cricothyroid muscle. The medial tension (compression) is obtained by contracting the lateral thyroarytenoid muscles. The adductive tension is caused by contraction of the inter-arytenoid/oblique arytenoid muscles and the lateral cricoarytenoid muscles. Each phonatory class has a different specification in terms of these physiological parameters. Fig- Three laryngeal parameters of muscular tension as described in Laver (1980)

13. Below, the influences of the tensions and adjustments of the vocal folds on the phonation process and on voice quality will be described briefly(after Eckert & Laver, 1994). Types Of Phonation Glottal states(from open to closed) Voicelessness(full airstream) Breathy voice(murmur) Slack voice(intermediate) Modal voice(maximum vibration) Stiff voice(intermediate) Creaky voice(restricted airstream) Glottalized(blocked airstream) Ballistic(fortis) Supra-glottal phonation F aucalized voice(hollow/yawny) Harsh/ventricular voice(pressed) Strident voice(epiglottal trilled) Non-phonemic phonation Whisper Falsetto Vibrato

14. Phonation types- Although each language may be somewhat different from one another ,but the degrees of phonation are classify into several categories. Glottal states - A series of seven alveolar stops, with phonations ranging from an open/lax to a closed/tense glottis, are: Open glottis voiceless(full airstream) breathy voice slack voice Sweet spot modal voice (maximum vibration) stiff voice creaky voice Closed glottis glottal closure (blocked airstream)

15. Voicelessness/nil phonation(full airstream) - If the vocal cords are completely relaxed( i.e., widely abducted vocal folds) with the arytenoid cartilages apart for maximum airflow, the cords do not vibrate. This is  voiceless  phonation. In voiceless phonation no sound is generated and no acoustic energy is injected into the vocal tract. Laryngeal settings- Arytenoid cartilages apart causes maximum airflow. T he vocal folds are too far apart to vibrate, but close enough that they can cause some turbulence in the airstream under the right circumstances. (This is what "voiceless" usually means.) An obvious example is the pronunciation of [h] at the beginning of a word like German [h   a   n t]. Voicelessness at higher flow speeds causes turbulence even with widely abducted vocal folds. This type of phonation is called breath. Fig- The tension and adjustment forces acting on the vocal folds during voicelessness

16. Breathy voice/murmured voice - Breathy phonation is characterized by vocal cords that are fairly abducted (relative to modal and creaky voice) and have little longitudinal tension , this results in some turbulent airflow through the glottis and the auditory impression of “ voice mixed in with breath ” (Catford 1977:99). Laryngeal settings -In breathy phonation vocal cords are vibrating but without appreciable contact. arytenoid cartilages further apart than in modal voice. Vocal fold vibration is inefficient and, because of the incomplete closure of the glottis, a constant glottal leakage occurs which causes the production of audible friction noise. Air flows through the vocal folds at a high rate. The vibrations' frequency of is just below the value typical of the modal voice. The tension and adjustment forces acting on vocal folds during breathy voice are- muscular tension is low, minimal adductive tension, weak medial compression and medium longitudinal tension of the vocal folds  Breathy voice differs from voiced whisper because of the weaker medial compression and the smaller degree of voicing effort. However, as pointed out by Laver (1980), there is no clear perceptual boundary between whispery and breathy voice. Slack voice - Slack voice  (or  lax voice ) is the pronunciation of consonant or vowels with a glottal opening slightly wider than that occurring in modal voice. Such sounds are often referred to informally as lenis or half-voiced in the case of consonants. Fig- The tension and adjustment forces acting on the vocal folds during breathy voice

17. Modal voice(maximum vibration) - The neutral mode of phonation is modal voiced phonation. It is characterized by the optimal combination of airflow and glottal tension that yields maximum vibration. In the normal case the vibration of the vocal folds is periodic with full closing or nearly closing of glottis ,so no audible friction noises are produced when air flows through the glottis. Laryngeal settings- All muscular adjustments are on a moderate level and the frequency of vibration, as well as loudness are in the lower to mid part of the range normally used in conversation. For voiced sounds the the glottis is closed or nearly closed. One of the characteristics of modal phonation is the build-up of the   contact between the vocal folds. The modal phonation of a male speaker occurs at an average of 120 Hz, while for a female speaker it is approx. 220 Hz. Fig- The tension and adjustment forces acting on the vocal folds during voicelessness

18. Stiff voice(intermediate) - The term stiff voice describes the pronunciation of consonants or vowels with a glottal opening narrower, and the vocal folds stiffer, than occurs in modal voice. Creaky voice(restricted airstream) - in which the arytenoid cartilages in the larynx are drawn together; as a result, the vocal folds are compressed rather tightly, becoming relatively slack and compact. It is also called vocal fry, the lowest vocal register and is produced through a loose glottal closure that permits air to bubble through slowly with a popping or rattling sound of a very low frequency. Creaky phonation is typically associated with vocal folds that are tightly adducted but open enough along a portion of their length to allow for voicing. Laryngeal settings for creaky voice: 1. Ventricular folds often compressed down on true vocal folds, 2. Moderately high medial compression, 3. Very little longitudinal tension. This phonation is produced with vibrating vocal folds but at a very low frequency. The vocal folds are strongly adducted and of weak longitudinal tension. Both this factors cause the vocal folds' thickening. Additionally, they may come in contact with the false folds creating an unusually thick and slack structure. The resulting low tension and heavy vibrating massare responsible for the slower and irregular vibration. Both subglottal pressure also the glottal airflow are lowered compared to modal phonation. Creaky phonation shows irregular periods (i.e. has no fundamental frequency) and has a comparatively low intensity. This voice sound in general is not used for communication but for performing art purposes. Strong adductive tension Weak longitudinal tension Moderately high medial compression Fig- The tension and adjustment forces acting on the vocal folds during breathy voice

19. Glottalized(blocked airstream) - Glottalization is the complete or partial closure of the glottis during the articulation of another sound. If the arytenoids are pressed together for glottal closure, the vocal cords block the airstream(i.e., in this final state the vocal folds are held firmly together, closing off the glottis all together), producing stop sounds such as the glottal stop, as a result of the obstruction of the airflow in the glottis, the glottal vibration either stops or becomes irregular with a low rate and sudden drop in intensity. Glottalization of vowels and other sonorants is most often realized as creaky voice (partial closure). Glottalization of obstruent consonants usually involves complete closure of the glottis; another way to describe this phenomenon is to say that a glottal stop is made simultaneously with another consonant. In certain cases, the glottal stop can even wholly replace the voiceless consonant. The term 'glottalized' is also used for ejective and implosive consonants. Ballistic(fortis) -Ballistic syllables are a phonemic distinction in Otomanguean languages. They have been described as characterized with increased sub-glottal pressure ( Mugele 1982) or laryngeal abduction (Silverman 1994). The acoustic effect is a fortis release of the consonant, a gradual surge in the intensity of the vowel, followed by a rapid decay in intensity into post-vocalic aspiration. They may thus be a form of phonation. Glottalization

20. Supra-glottal phonation - The ''supra-glottal phonation'' would be made from the vibration of ''supra-glottal structures'' such as the false vocal folds, the arytenoids and the epiglottis, etc. In the last few decades it has become apparent that phonation may involve the entire larynx, with as many as six valves and muscles working either independently or together. From the glottis upward, these articulations are: glottal (the vocal cords), ventricular (the 'false vocal cords’), arytenoid, epiglotto -pharyngeal, raising or lowering of the entire larynx, narrowing of the pharynx. Until the development of fiber-optic laryngoscopy, the full involvement of the larynx during speech production was not observable, and the interactions among the six laryngeal articulators is still poorly understood. However, at least two supra-glottal phonations appear to be widespread in the world's languages. These are harsh voice ('ventricular' or 'pressed' voice) and faucalized voice ('hollow' or 'yawny' voice). There is another supra-glottal phonation known as strident voice. Harsh voice - Harsh voice , also called ventricular voice or (in some high-tone registers) pressed voice, is the production of speech sounds (typically vowels) with a constricted laryngeal cavity, which generally involves epiglottal co-articulation. Harsh voice includes the use of the ventricular folds (the false vocal cords) to damp the glottis in a way similar to what happens when a person talks while lifting a heavy load, or, if the sound is voiceless, like clearing one's throat. It contrasts with faucalized voice, which involves the expansion of the larynx. Harsh voice is due to the very strong tension of the vocal folds (especially medial compression and adductive tension), which results in an excessive approximation of the vocal folds. When the whole larynx is subjected to this extremely high tension, the upper larynx becomes highly constricted with the ventricular folds pressing on the upper surfaces of the vocal folds, making their vibration ineffective. Fig- The tension and adjustment forces acting on the vocal folds during harsh voice

21. Faucalized voice - Faucalized voice, also called hollow voice or yawny voice, is a vocal quality of speech production characterized by the vertical expansion of the pharyngeal cavity due to the lowering of the larynx. It is termed ‘ faucalized ’ because of the stretching of the fauces and visible narrowing of the faucial pillars in the back of the oral cavity. During faucalized voice, the sides of pharynx expand outward and the larynx descends and tilts forward. The term "yawny voice" is appropriate to compare this voice quality to the physiological act of yawning. Its opposite is harsh voice, a vocal quality produced when the pharynx is contracted and the larynx raised. Faucalized voice is not to be confused with breathy voice, which involves relaxed vocal folds, greater velocity of airflow through the glottis and produces a lower pitch sound. Faucalized voice involves the forward tilting of the larynx which stretches the vocal folds and produces a higher pitch sound, despite the increased volume of the pharyngeal cavity. Strident voice (epiglottal trilled) - Strident vowels (also called sphincteric vowels) are strongly pharyngealized vowels accompanied by an epiglottal trill, with the larynx being raised and the pharynx constricted. Either the epiglottis or the arytenoid cartilages thus vibrate instead of the vocal cords. That is, the epiglottal trill is the voice source for such sounds. Stridency may be a type of phonation called harsh voice. A similar phonation, without the trill, is called ventricular voice; both have been called pressed voice.

22. Non-phonemic phonation - Whisper - Whispering is an unvoiced mode of phonation in which the vocal cords are abducted so that they do not vibrate; air passes between the arytenoid cartilages to create audible turbulence during speech. Supralaryngeal articulation remains the same as in normal speech. In normal speech, the vocal cords alternate between states of voice and voicelessness. In whispering, only the voicing segments change, so that the vocal cords alternate between whisper and voicelessness (though the acoustic difference between the two states is minimal). Whisper phonation is characterized by a triangular opening of the cartilaginous glottis (the shape of an inverted Y). Adductive tension is very low and medial compression, as well as longitudinal tension, are moderately high. Whisper sound quality is produced through turbulences generated by the friction of the air in and above the larynx with vocal folds not vibrating. Falsetto - Falsetto is the vocal register occupying the frequency range just above the modal voice register and overlapping with it by approximately one octave. The vocal folds are stretched longitudinally, thus becoming relatively thin. Consequently, the vibrating mass is smaller and the generated tone higher. The adduction of the folds is high and the medial compression is also strong . It is produced by the vibration of the ligamentous edges of the vocal cords, in whole or in part. Commonly in the context of singing, falsetto, a characteristic of phonation by both sexes, is also one of four main spoken vocal registers recognized by speech pathology. The term falsetto is most often used in the context of singing to refer to a type of vocal phonation that enables the singer to sing notes beyond the vocal range of the normal or modal voice. Vibrato - is a musical effect consisting of a regular, pulsating change of pitch. In singing it can occur spontaneously through variations in the larynx. Fig- The tension and adjustment forces acting on the vocal folds during whisper Fig- The tension and adjustment forces acting on the vocal folds during falsetto

23. Physiology of Phonation- Phonation is a series of openings and closings of the vocal folds which have two phases. 1.Pre-phonation phase: during this period VFs move from abducted position 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 vocal folds are approximated call medial compression (force with which folds brought together), caused by action of adductor muscles (lateral cricoarytenoid, transverse arytenoid). The posterior cricoarytenoid muscles (abductors) prevents the arytenoids from sliding forward. 2.Attack phase: begins with the vocal folds in the adducted position and extends through the initial phase of the vibratory cycle. Complete adduction is not required for the initiation of phonation, however sufficient subglottal pressure ( Psub ) is required (3-5 cm H2O). Three types of attacks: breathy (resp. occurs before VFs adduction), simultaneous (VFs adduction and resp. occur at the same time )and glottal (resp. after VFs adduction). 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 series 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).

24. Mechanisms of phonation: The phonatory process, or voicing, occurs when air is expelled from the lungs through the glottis, creating a pressure drop across the larynx. When this drop becomes sufficiently large, the vocal folds start to oscillate. Phonation is accomplished by alteration of the angle between the thyroid and cricoid cartilages (the cricothyroid angle) and by medial movement of the arytenoids during expiration. These movements result in fine alterations in vocal fold tension during movement of air, causing vibration of the vocal folds. Lesions or malfunctions of the vocal folds (e.g., inflammation, papilloma, paresis) therefore affect phonation. Phonation is the only laryngeal function that alters the cricothyroid angle. Therefore, despite significant airway obstruction during inspiration, it may still be possible to phonate. In preparation for phonation (or for breath holding), the arytenoids can be rotated and translated medially by contracting the lateral cricoarytenoid and interarytenoid muscles. These contractions have the effect of moving the vocal fold surfaces toward each other, or adducting them, to reduce or eliminate the glottal airspace. Contraction of the thyroarytenoid muscle tends to slide the arytenoids anteriorly, decreasing the distance between the vocal processes and the thyroid prominence, and consequently shortening the vocal folds. The cricothyroid muscles originate on the anterior surface of the cricoid cartilage and insert on the inferior edge of the thyroid laminae. Their contraction tends to rotate the cricoid and thyroid cartilages toward each other, having the effect of increasing the distance between the vocal processes and the thyroid prominence, thereby lengthening the vocal folds. Thus, the thyroarytenoid and cricothyroid muscles are effectively configured as an agonist/antagonist pair and their relative degree of activation can precisely adjust the overall length of the vocal folds.

25. In summary, the cartilages of the larynx form a structure that supports and houses the vocal folds. When differentially contracted, the intrinsic laryngeal musculature can move the cartilages relative to one another in order to open and close the glottis through abductory and adductory maneuvers, respectively, as well as to modify the length and mechanical properties of the vocal fold tissue. It is important to note that these movements are executed on a time scale similar to the other articulators such as the tongue, lips, jaw, and velum, and do not in themselves generate vibratory motion of the vocal folds, and hence, do not pro-duce sound. Vibration, which causes a portion of the vocal folds to move back and forth hundreds of time per second and produces sound, occurs when the configuration of the medial surface of vocal folds, their mechanical properties, and the aerodynamic conditions surrounding them is sufficient to initiate and sustain self-oscillation. The vocal folds will not oscillate if they are not sufficiently close to one another, are not under sufficient tension or under too much tension, or if the pressure drop across the larynx is not sufficiently large. f vocal cord oscillation/ theories of vibration of vocal cords Theories of Vibration of the Vocal Folds: A number of different theories has been proposed to explain the vibration of the vocal folds during speech, while many are no longer supported by recent evidence. There are currently two main theories as to how vibration of the vocal folds is initiated: the myoelastic theory and the aerodynamic theory . These two theories are not in contention with one another and it is quite possible that both theories are true and operating simultaneously to initiate and maintain vibration. A third theory, the neurochronaxic theory , was in considerable vogue in the 1950s, but has since been largely discredited.

26. Neurochronaxic theory The Neurochronaxic Theory specified that the vibratory cycles (of voice) resulted from neural pulses serially activating the VF muscles, thereby making them move over and over to (and from) the laryngeal midline and movement away from midline contact was aided partly by muscle relaxation and subglottal air pressure. To reiterate, each cycle occurred only when the contracting process was repeated—with the entire operation replicated again and again in order to create a vocal tone. Fundamental frequency (F ) was determined simply by the number of neural activations (of the relevant VF muscles) which occurred each second. To produce phonation with an F of 100 Hz, the neural system had to fire, and the VF muscles contract, 100 times each second. For phonation at 1000 Hz, 1000 contractions a second were required. [ i.e., This theory states that the frequency of the vocal fold vibration is determined by the chronaxie of the recurrent nerve, and not by breath pressure or muscular tension. According to this theory every single vibration of the vocal folds was due to an impulse from the recurrent laryngeal nerves and that the acoustic center in the brain regulated the speed of vocal fold vibration. Each vibration, therefore, represented the result of beat-by-beat impulses through the recurrent laryngeal nerve]. Problems with this theory - neurophysiologists suggested that these very high rates of muscle contraction were physiologically impossible as the muscles have been shown to not be able to contract fast enough to accomplish the vibration. In addition, persons with paralyzed vocal folds can produce phonation, which would not be possible according to this theory. Phonation occurring in excised larynges would also not be possible according to this theory.

27. MYOELASTIC-AERODYNAMIC THEORY ‘ Myoelastic ’ refers to the laryngeal muscle (that is covered by a elastic layer which are superficial lamina propria, squamous epithelium, and intermediate and deep lamina propria) activity that occurs during phonation and the effects of laryngeal muscle activity on the elasticity of vocal folds(VFs) ‘Aerodynamic’ refers to the aerodynamic determinants of the vibratory cycle, i.e., the opening and closing phase of vibration. The Myoelastic Theory suggest that phonation occurs when the VF are adducted by a general contraction of the relevant laryngeal muscles and then blown apart by subglottal air pressure. i.e., this theory states that when the vocal cords are brought together and breath pressure is applied to them, the cords remain closed until the pressure beneath them, the subglottic pressure, is sufficient to push them apart, allowing air to escape and reducing the pressure enough for the muscle tension recoil to pull the folds back together again. The next cycle occurs when the folds are adducted again, but this movement is created essentially by elastic recoil. [i.e., The pressure builds up once again until the cords are pushed apart, and the whole cycle keeps repeating itself]. The process is repeated over and over to create sound. The rate at which the cords open and close, the number of cycles per second, determines the pitch of the phonation. Proponents of the theory also proposed that different F could be produced by changes in the mass and stiffness of the adducted VF, and variation of voice quality and intensity could be accomplished by other VF manipulations (e.g., size, structure, “tension”, etc.)—all of which would result in phonation when coupled to aerodynamic support. This theory did experience some difficultly explaining just how certain sounds were made or why air pressure appeared to systematically vary for different types of phonation.

28. The Aerodynamic Theory is based on the Bernoulli energy law in fluids. The Aerodynamic Theory, resulted from observations made of airflow through tubes. Its proponents indicated that their theory was based on the well-known fact that the velocity of airflow is increased—but its pressure reduced—when air streaming through a tube was impeded by the narrowing of channel diameter—i.e., by the Bernoulli effect. The theory states that when a stream of breath is flowing through the glottis while the arytenoid cartilages are held together (by the action of the interarytenoid muscles), a push-pull effect is created on the vocal fold tissues that maintains self-sustained oscillation. The push occurs during glottal opening, when the glottis is convergent, and the pull occurs during glottal closing, when the glottis is divergent. Such an effect causes a transfer of energy from the airflow to the vocal fold tissues which overcomes losses by dissipation and sustain the oscillation. i.e., Increase in laryngeal airflow and reduction in pressure—resulting from the VF projecting into the laryngeal tube—would produce a sucking action relative to the folds. This action, in turn, would pull them toward each other. Thus, this theory suggested (at first anyway) that all that was needed for phonation was airflow over the VF as they projected into the airway. They would be sucked together (adducted) until closed and then pushed away from the midline by the increase in subglottic pressure (which occurred once the airway was blocked). The problem here was that this theory did not explain how many of the frequency and quality changes associated with phonation occurred, why different VF lengths, shapes, etc. had been observed, or why changes in VF configuration appeared to be directly associated with different types of voice.

29. Fig-Vibration of vocal folds according to Myoelastic -Aerodynamic theory air pressure beneath the folds (Subglottal pressure) blows folds apart when this air pressure becomes strong enough, it overcomes the resistance of the closed vocal folds and pushes them apart or away from midline. At first the superior aspect of the vocal folds now begin to open because of the pressure buildup. air passes through the vocal tract, setting the air within the tract into vibration (airstream sets vocal folds into vibration) puff of air is released due to folds elasticity(elastic recoil force) begin to recoil back as the folds begin to close, they form a narrow channel - air passing through this channel increases in velocity, so the air pressure decreases or becomes negative(Bernoulli effect) Creates a vacuum – bring vocal folds back together(closed) [When the vocal folds are in the midline, they now contacts inferiorly with each other], The pressure builds up once again until the cords are pushed apart, and the whole cycle keeps repeating itself.

30. Body Cover theory The body cover theory explains that true vocal folds have technically 3 functional layers. The three functional layers are cover (which is composed of squamous epithelium or mucosa and the superficial lamina propria), transition layer which are vocal ligament (composed of intermediate and deep lamina propria) and body (consist of thyroarytenoid muscle and vocalis muscle). The Body-Cover (Hirano1974) concept simply stated that the morphology of the vocal fold divided (mechanically) into division between two groups of tissue layers (cover and body) that are set into vibration by the glottal airstream. The groups are coupled in the lateral direction, but have rather different mechanical properties. The body cover theory states that the cover which is epithelium and superficial lamina propria vibrates around the muscle. The muscle provides the structure but the cover acts as the one that moves freely and the one that vibrates. Fig-Layers of vocal folds: anatomical tissue layers compared with functional layers in the body-cover model Fig-functional layers of vocal folds according to the body-cover theory

31. The cover is very pliable and has no contractile properties, that act as a flexible sheath around the body layer. The cover, being heavily irrigated with liquid, can propagate a surface wave that facilitates energy transfer from the glottal airstream to the vocal-fold tissues. Its tension is controlled by vocal-fold length. The inner group, or body is less deformable and has active contractile properties. Its tension is therefore not only determined by length, but also by active stiffening of the muscle internally. The combined tension of the portions of the body and cover in vibration would seem to regulate the fundamental frequency of oscillation. The cover is loosely connected to the body during vibration. The motion of the cover layer is usually observed as a surface wave that propagates from the bottom of the vocal fold to the top thus experiencing movement in both the lateral and vertical directions. Self-sustained vocal-fold oscillation is highly dependent on this surface-wave behavior (typically referred to as the vertical phase difference) and is the primary mechanism for transferring energy from the glottal flow stream to the tissue to fuel the vibration. The body layer is primarily involved in lateral motion. Based on his findings, Hirano (1974) suggests that the vocal fold should be treated as a double structured vibrator whose stiffness parameters should be based on the relative activations of the thyroarytenoid (TA) and cricothyroid (CT) muscles. Thus the resultant vibration of the vocal folds is composed of the coupled oscillations of the body and cover layers. Body-Cover theory is associated with the myoelastic -aerodynamic theory-how the vocal folds come together bottom to top-upper and lower mass front to back-like a zipper.

32. Mucosal wave The mucosal wave is the wave-like movement of the vocal fold cover (epithelium and superficial layer of the lamina propria) during vibration. An exact, agreed upon definition of mucosal wave is difficult to find, as there seems to be some disagreement among experts in the field. That being said, the mucosal wave is generally agreed to encompass the differential between the lower and upper margins of the vocal folds as can be seen during the closing phase of vibration. There is disagreement about whether the movement of the mucosa on the superficial aspect of the vocal fold during the closed phase of vibration should be included in the term mucosal wave, although many clinicians do include an evaluation of this movement in their assessment of the mucosal wave. Furthermore, there is an upward swelling or vertical motion of the mucosa prior to the opening phase that some have included in their definition of mucosal wave. The mucosal wave depends on the ability of the superficial vocal fold tissues to vibrate independently from the deeper structures and requires that the relationship of the vocal fold histologic layers be in balance. The mucosal wave is therefore not just an indicator of the health of the superficial tissue. It also provides information regarding the underlying layers of the lamina propria and the thyroarytenoid muscle. The mucosal wave can be impacted by not only the vocal fold anatomy but also by changes in the loudness and pitch of phonation. High-pitched phonation is associated with a smaller mucosal wave, and conversely, low-pitched phonation is associated with a larger mucosal wave. Clinicians should expect the mucosal wave to decrease when gliding from habitual to high-pitched phonation. This occurs with lengthening of the vocal folds due to contraction of the cricothyroid muscle. The superficial vocal fold tissues are placed on stretch at higher

33. frequencies of vibration leading to a decrease in the amount of available movable tissue. The cricothyroid muscle acts like a person pulling on two ends of a rubber band: as the rubber band stretches, the rubber gets thinner. The reduction in mass of the vibratory portion of the vocal folds, which causes them to vibrate faster, also reduces the tissue available for production of the mucosal wave. The opposite is true for lower-pitch phonation. When a person purposefully phonates in a lower pitch, he or she relaxes the thyroarytenoid muscles and allows for an increase in pliable mucosa that can “blow in the wind” of exhalation. mucosal wave holds true for vocally normal speakers voluntarily increasing or decreasing the pitch of their phonation and should not be applied to persons with voice disorders that cause high- or low-pitched phonation. Louder phonation is associated with a larger mucosal wave, and conversely, softer phonation is associated with a smaller mucosal wave. Clinicians should expect an increased mucosal wave with louder phonation as a result of the build-up of greater subglottal pressure. The larger subglottal pressure is required to initiate and sustain vocal fold vibration in the presence of increased medial compression of the vocal folds mediated by the lateral cricoarytenoid, thyroarytenoid, and the interarytenoid muscles. Softer phonation is associated with less medial compression and less subglottal pressure. Thus, softer phonation does not have the physical properties that would create a larger mucosal wave. Mucosal wave is judged with stroboscopy during phonation with a normal pitch and loudness. Mucosal wave should also be judged during high- and low-pitched phonation and during loud and soft phonation to ensure that the changes in mucosal wave. Given that the mucosal wave is generally defined as the differential between the lower and upper margins of the vocal folds, as can be seen during the closing phase of vibration, we need stroboscopy , kymography, or high-speed videoendoscopy to be able to see the mucosal wave.

34. Fig- Amplitude of vibration measured from stroboscopic recordings of (A)habitual pitch and loudness (B)pressed phonation (C)high-pitch phonation (D)low-pitch phonation Figure - A vibratory cycle is considered to be 360 degrees. The images were taken at 45 degree phases of the cycle demonstrating the progressive opening and closing of the vocal folds as they vibrate. If each image is shown one after the other as a movie changes in the a mucosal wave can be seen

35. Glottal cycle The vocal folds alternately trap and release air; each trap/release is one cycle of vibration. This cycle is often referred to as the glottic cycle, and it is divided into phases: opening phase, open phase, closing phase, closed phase. During the closed phase, the air pressure builds up below the vocal folds. When the glottis opens, the air explodes through the vocal folds, and that's the beginning of the sound wave. The strength of that explosion determines the loudness of the sound coming directly from the larynx. First, the laryngeal muscles position the vocal cords in various degrees of adduction and place them under the appropriate longitudinal tension. Next, muscular and passive forces of exhalation cause the subglottic air pressure to increase. When this subglottic pressure reaches a point where it exceeds muscular opposition, the glottic chink is forced to open. When the vocal cords start opening from complete closure, they open in a posterior to anterior direction with the posterior portion of the glottis opening first, reaching maximum excursion first, and recontacting each other at the end of the vibratory cycle prior to the anterior portion of the cords. After release of the puff of air there is a reduction of subglottic pressure, and the vocal cords approximate each other again ( myoelastic forces of the vocal cords have exceeded the aerodynamic forces). The myoelastic forces are enhanced because air current flowing through a narrow channel exerts a negative pressure on the channel walls; This is the basis of Bernouilli's Principle. The vocal cords are thus sucked back together in an adducted state until the subglottic air pressure can overcome the myoelastic forces of the reapproximated cords, and the cycle is then repeated.

36. Phonatory abnormalities When vocal folds do not work harmoniously, impairment in general quality of the voice. Common types of impaired phonation: Hard glottal attack - Hard or abrupt glottal attack (HGA) is one of the vocal behaviors often associated with benign lesion of the vocal folds. ‘Hard Glottal Attack’ describes the action of the vocal folds slamming together quickly and forcefully before sound begins, causing an increase in muscular tension in the laryngeal area. Glottal fry - glottal fry is recognized when the vocal folds vibrate very slowly, making the voice appear “crackly” or “creaky”. It is the lowest vocal register and is produced through a loose glottal closure that permits air to bubble through slowly with a popping or rattling sound of a very low frequency. Breathy phonation - Breathy-pressed phonation is an easily identified dysphonia that combines two phenomenologies – audible muscular effort + a breathy, air-wasting quality. Spasticity- Spasticity is a condition in which muscles stiffen or tighten, preventing normal fluid movement. The muscles remain contracted and resist being stretched. Spasticity is generally caused by damage or disruption to the area of the brain and spinal cord that are responsible for controlling muscle and stretch reflexes. Hoarseness- Hoarseness is an abnormal change in the voice caused by a variety of conditions. The voice may have changes in pitch and volume, ranging from a deep, harsh voice to a weak, raspy voice. Hoarseness is generally caused by irritation of, or injury to, the vocal cords. Hoarseness can be caused by a number of conditions. The most common cause of hoarseness is acute laryngitis (inflammation of the vocal cords). Other causes of hoarseness include: benign vocal cord nodules, cysts or polyps, vocal cord paralysis, gastroesophageal reflux (GERD), allergies, inhalation of respiratory tract irritants, smoking.

37. References- https://en.wikipedia.org/wiki/Phonation https://www.slideserve.com/emiko/voicing-phonation https://www.ims.uni-stuttgart.de/institut/arbeitsgruppen/ehemalig/ep-dogil/EGG/page10.htm https://www.slideserve.com/hall-cobb/physiology-of-phonation https://anaphyslp.wordpress.com/2020/10/20/theories-on-phonation/ https://quizlet.com/5085570/theories-of-phonation-flash-cards/ https://www.slideshare.net/ravindradaggupati/physiology-of-larynx-theories-of-voice-productiondrravindra-daggupati https://www.aans.org/Patients/Neurosurgical-Conditions-and-Treatments/Spasticity https://laryngopedia.com/breathy-pressed-phonation-or-dysphonia/ https://www.medicinenet.com/hoarseness/article.htm