Phonation
CSD 345: Hearing and Speech Science

               

Module Objectives

1.  Review the anatomy and physiology of laryngeal structures.

2. Describe the Bernouilli effect and the myoelastic aerodynamic theory as they pertain to vocalization.

3. Describe methods of measuring laryngeal function and compare various types of instrumentation for laryngeal measurement.

4. Analyze the voice of individuals of two different ages and compare fundamental frequency and voice intensity.

 

Module objectives relate directly to these course objectives:

Course Objective 1: Describe the functioning of laryngeal structures for speech production.

Course Objective 2: Demonstrate a basic knowledge of voice fundamental frequency and voice intensity.

Course Objective 4: Analyze speech and voice by using instrumental and non-instrumental assessments and interpret the measurements obtained.

 

The following will help you meet the objectives of the module:

1. Read the chapter on Phonation in your Raphael et al. (pages 69-87).

3.  Complete the activities in the course module to give you more practice with the material.

4. Complete the lab project in the assessments t.

5.  Take the quiz in the quiz tool to assess your knowledge of phonation.

 

Review of Laryngeal Anatomy

As we learned in Module 1, the lungs provide the air source for phonation.  The air from the lungs drives the vocal folds, and the upper airway shapes the air source into speech.

The air pressure on the vocal folds produces a periodic sound wave. This periodic sound wave is phonation.  Vowels are one class of sounds that will produce a periodic sound wave. Of course, we can produce aperiodic sounds, such as noises and sounds like "shhh." Most sounds produced in beatboxing would qualify as aperiodic.  We can also produce a combination of periodic and aperiodic noises, such as a voiced "hiss."

 

Let's go over some anatomy. The larynx is located on top of the trachea, below the hyoid bone. You can see a picture of this in your textbook, figure 4.2 on page 72, and in these pictures from Netter. Note the hourglass shape of the view of the larynx in your textbook.

larynx.jpg Source: McFarland, D. H. (2008). Netter's Atlas of Anatomy for Speech, Hearing, and Swallowing, Mosby

 

There are several functions of the larynx, which:

 The cartilages of the larynx

The larynx has three cartilages: the thyroid, the cricoid, and the paired arytenoid cartilages. The laryngeal cartilages support the muscles that shape the vocal tract. You can see from the Netter illustration on the left that the cricoid cartilage looks like a signet ring; the front and sides are narrow, and the back is the signet. The arytenoids are pyramidal shaped, and are perched on the top of the cricoid in the back. The thyroid cartilage lies anterior to the arytenoids, and the sides of this cartilage encloses the arytenoids. You can see the angle in the Netter picture in the top left illustration. The size of the angle differs for men and women.

 

 

 

Movement of the larynx

larygeal muscle movement.jpg The thyroid and cricoid can rock back and forth upon each other to change pitch, and the arytenoids can rotate and rock on the cricoid cartilage and can slide a little towards each other. This Netter illustration shows some of the laryngeal muscles and how they move the cartilages and vocal folds (from Netter, F. (2010) Atlas of Human Anatomy 5, Saunder.)

 

Take a look at this video. You can see the arytenoid cartilages moving the vocal folds together at the midline.

 

 

 

Anatomy of the vocal folds

laryngeal musculature.jpg As can be seen in Figure 4.4 of your textbook (page 73) the vocal folds converge in the front of the thyroid cartilage, diverge posteriorly, and attach to the sides of the arytenoid cartileges. The vocal folds' tension and elastic can be changed--they can be made thicker, thinnner, shorter/longer, widely separated, or brought together. They can also be elevated or depressed. This can all be accomplished by the laryngeal muscles, which you saw on the previous page and can see on the Netter slide here.

from Netter, F. (2010) Atlas of Human Anatomy 5, Saunder.)

 

Note that you will not have to know the names and functions of all laryngeal muscles for the exam. The muscles that you should know for the exam are those that are highlighted in the notes. For example, the crichthyroid muscle plays a large role in increasing frequency. Generally, the Netter slides are here for your review, to help you visualize the physiology of laryngeal movement.

 

The glottis is the space between the vocal folds. The size of the glottis is determined by the configuration of the vocal folds. Glottal size is increased through vocal fold abduction, and decreased through adduction.

 

The false vocal folds

The false vocal folds (or ventricular folds) are located superiorly to the true vocal folds. You can see a picture of these on page 72 of your textbook, figure 4.2. They are incapable of adducting. They do move with the arytenoids, but do not vibrate.

 

The movement of the vocal folds can act as resistance to the airflow from the lungs. Test your knowledge of this by taking the quiz below.

 Show quiz group

 

 

 

 

 

 

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Physiology of vocal fold vibration

The vocal folds work on the same principal as the "raspberry," which you can see here.

 

Like the man's lips and tongue in this video, the vocal folds are blown apart by air flow from the lungs, rather than being innervated by a nerve. Nerve innervation would be too slow--the vocal folds vibrate up to 100 times per second. The vocal folds are able to vibrate so rapidly because they are elastic--they come back together after being blown apart. The theory that explains vocal fold movement is the myoelastic aerodynamic theory of phonation, described in your textbook on page 70. The "myoelastic" describes the characteristics of the vocal folds, and the "aeordynamic" describes the movement of air past the vocal folds. Its principles are illustrated in the material that follows on this page of the module.

 

The diagram below is from your textbook, page 78. Let's look at it to see what happens to the vocal folds as air moves from the lungs to the oral cavity. These 8 frames show 1 cycle of vocal fold vibration. During each cycle, 1 puff of air is emitted.

 

 

IMG_0002.jpg In A', you can see the vocal folds are being brought together in the midline for phonation. You can see that they are fairly thick. The air is trying to exit the lungs. Subglottal pressure is increasing because the glottis is closed by the vocal folds. Remember Boyle's law from the unit on respiration? When volume gets smaller, pressure increases.

 

In B', we see that the increasing pressure can force the vocal folds away from the midline at the bottom.

 

In C', the pressure wave pushes itself upward and a puff of air emerges.

 

In D', the vocal folds are blown apart.

 

In F', the vocal folds return quickly to the midline. The arytenoid cartilages are still together, so the vocal folds are stretched. You can see that the vocal folds first return at the bottom. There is an aerodynamic effect here: the space at the bottom is narrower than the space at the top, so because of velocity the bottom closes first. The pressure at the bottom of the vocal folds is more negative than at the top. The two forces that bring the vocal folds togetehr in F' are 1) tissue elasticity, and 2) the Bernoulli effect.

 

 

 

 

 

The Bernouilli Effect

When air or liquid flows through a constricted passage, the velocity increases. If a volume of air is held constant, the velocity of air flow through a constriction is increased. You might think of this using the analogy of a creek converging on a constriction, or people converging on a turnstile. Lots of water is coming through a constriction, and lots of people are going through a turnstyle, and velocity increases in the constriction or turnstyle. In nature, no one waits their turn.

The increase in velocity results in a drop in outward pressure.  So, Bernouilli's law means that the greater the velocity, the lower the static pressure. The picture in your text, page 78 figure 4.12 illustrates this. In the constriction, pressure is decreasing and becoming negative (a type of suction).  Reduction in outward pressure moves the vocal folds towards each other.  Blowing them apart creates a narrow space which causes the air pressure within the glottis to decrease. In the picture below, the pressure to the left of the vertical line is less than the pressure to the right of it, as the air passes through the tube.

 

bernouilli effect.png

Airplanes fly due to the Bernouilli effect. The speed of air against an airplane wing causes a pressure drop, which raises the wing.  You can see a diagram of this on page 79 in your text. You can illustrate this effect by putting a tissue under your chin and then blowing. The airflow above the tissue is faster than the aiflow below, creating lower pressure on the top of the tissue than the bottom, causing the tissue to rise. Another example your textbook gives is airflow down a hallway. Doors that are open will slam shut, because pressure is lower in the periphery of the hall than the center. This video is a demonstration of the Bernouilli effect.

 

 

How does the Bernouilli effect apply to the vocal folds?

The vocal folds are physically closer to each other at the bottom, and the velocity will be greater at that level. Thre is also a phase difference--the patterns of vibration are different between the inferior and superior portions of the vocal folds. This is called the vertical phase difference. The pressure will be less at the bottom due to the lower velocity. This is why the bottom part of the vocal folds comes together more quickly, which you have seen in picture F' in figure 4.11. The vocal folds can start vibrating before they have contact with each other because of the Bernoulli effect (for example, during /h/ in the word "hear").  the vocal folds will come together for the vowel /i/ after /h/.

 

 

Frequency

Frequency, in the context of this course, is a measure of a cycle of vibration per unit time. For voice, it is equal tothe number of times the vocal folds open and close per second. The vibration of a tuning fork results in a pure tone, as the fork vibrates at only one frequency. The vibration of the vocal folds is much more complex, due to the structure of the vocal folds. Vibration of the vocal folds produces a complex tone, one that is composed of several frequencies of vibration. Fundamental frequency is the lowest frequency component of the complex tone. Frequency relates directly to pitch, which is perceptual.

 

simple.complex.wave.png harmonic spectra.png

 

The image on your left is from your textbook, page 27. It illustrates two waveforms. The top is a sinusoidal wave of a sound that may be produced by a tuning fork--a pure tone. The bottom waveform is that of a complex wave, with more than one frequency component.

 

 

We judge pitch to correspond to the fundamental frequency of a harmonic series. The image on the right, from your textbook, page 80, illustrates harmonic series produced by an adult and a child. A complex tone of 600, 900, and 1,200 Hertz (Hz) is judged to have a pitch of a 300-Hz tone. This is the rate at which the basic pattern of the complex wave repeats itself.

 Show quiz question

 

 

 

Frequency and voice: a look at the musical scale and voice registers

singing.voice.jpg The rate of vocal fold vibration is described either in terms of fundamental frequency (cycles per second or Hz), or in terms of musical notes (pitch). In either case the scale is on a continuum ranging from less than 60 Hz (B1 on the musical scale) in the basso voice to over 1588 Hz (G6 on the musical scale) in the soprano voice.

Looking at the picture on the left (from Zemlin, W. R. (1998). Speech and Hearing Science: Anatomy and Physiology (4th ed.), p. 166.  Boston: Allyn & Bacon), you can see that there are five registers (numbered 1-5) covering a range of notes, and the registers are different for males and females. The registers overlap. No one person has all 5, and good singers have 3 registers. The concept of registers is controversial in singing, with some authors designating 4 registers. But in speech pathology, register is associated with vocal fold vibration.

 

The names of the registers vary. In singing, the "head" voice is associated with the position and use of the vocal folds and larynx. It is used in singing and found in all voice types, from bass to soprano. In the "head" register (number 4 on the picture), vocal folds are thin, and there is no firm glottal closure. The cricothyroid muscles are active. Singers say the sound vibrates in their in their heads rather than chest. "Chest" register (number 4 on the picture) is the range of notes below midle C (C4 on the picture). This is the lower half of a person's vocal range. The pitch is said to resonate throughout the chest cavity.

 The musical scale is organized into octaves, with a fequency ratio of 2 to 1. So, for example, 1 octave above a 500-Hz tone is a 1,000-Hz tone. C4 is middle C, and you can see on the picture to the left that it is 256 Hz. Actually, the "standard" for Middle C is 261.63 Hz. If we want to find an octave below middle C, we divide by 2 to get 130.81 Hz, or C3. The note A4 is an international standard at 440 Hz. If we have a tuning fork set at this standard, it will vibrate at 440 Hz. If we tune a piano precisely to this value, everything else is in proportion to that.

 Show quiz question

  For the speaking voice, there are three registers. Modal register is commonly used when speaking, and corresponds to the singing "chest" register. Pulse register is the lowest register. You could technically speak in pulse register, but it would be difficult. Pulse register typically occurs at the end of an utterance, and has a double vibratory pattern. It is a "creaky" voice, also known as glottal or vocal fry. The vocal folds in this register are short and thick. The highest register is the loft register. This register is also called falsetto. The vocal folds are long, stiff, and very thin along the edges, and somewhat bow-shaped. The vocalis and cricothyroid muscles are stiff, and the vocal folds may not be completelly closed. In singing, the loft register corresponds to the "head" voice.

  

Factors that affect frequency

The size of the vocal folds determines fundamental frequency. A greater length and higher mass lower frequency. Men have vocal folds that are approximately 17-24 millimeters (mm) in length, and women's vocal folds are 13-17 mm.

The fundamental frequency for males averages 130 Hz, for females, 220Hz, and for children, 300 Hz.

Mutations are voice changes, which are due to the rapid growth of the larynx that occurs during puberty. Before puberty, both boys and girls have fundamental frequencies of aproximately 270-300 Hz. Voice changes are more recongnizable in males than females. Changes in the boy's voice are approximately 1 octave, from approximately 270 to 120 Hz, as the vocal folds grow longer and thicker. The boy's singing ability is not as good after the change. In females, the change is about 2-3 tones, rather than 1 octave, with a change from 270 to 220 Hz.

 

Frequency is proportional to tension, stiffness, and elasticity over mass. The relationship can be depicted in this equation:

f α k/m

f = frequency

k = tension, stiffness, elasticity

m = mass

α = is proportional to

 

This relationship helps us compare the speaking voice between people, for example, an adult male and a small child. The larger the vocal folds, the lower the frequency. This formula holds within an individual, too--if a person chooses to vary his frequency, he is going to manipulate the variables of tension, stiffness, elasticity, and mass.

 

Raising Frequency

We raise frequency through the action of the laryngeal muscles. Even before we make a sound, the vocal folds get shorter--the arytenoid cartilages come together medially and anteriorly. The vocal folds are shorter during phonation than at rest breathing. Remember that the cricothyroid muscle contracts to lengthen the vocal folds. The cricothyroid is the most important muscle in raising frequency. As the vocal folds are stretched, their mass per unit length decreases. The stretching also increases the stiffness factor. It can be represented in this way:

k↑  

m↓ The net result is that frequency is increased.

 

We can also increase the internal tension of the vocal folds. The most medial part of the vocal folds (the thyroarytenoid muscle) is the vocalis muscle. If the vocalis contracts, it increases the internal tension of the vocal folds, and increases the stiffness. In the equation, it is represented like this:

k↑  

m Note that mass does not decrease, and the net result is that frequency is increased.

 

Frequency can be increased through the lateral cricoarytenoid muscle. Remember that the lateral cricoarytenoid attaches to the cricoid and attaches to muscular processes for medial compression. The medial compression restricts the vibrating mass to more of the anterior position of the vocal folds. The action is similar to putting frets on a guitar--it reduces the vibrating mass, which is one way to increase frequency. The formula is depicted here:

 

Lowering Frequency

Whereas the cricothryoid muscle raises frequency, there's not much evidence that points to one muscle to lower frequency. If you think about the thyroarytenoid muscle in its broadest sense, as it contracts, it draws the vocal folds together. As it contracts, it draws the vocal folds together, and they become shorter, thicker, and more relaxed. The formula is depicted here:

 

k_↓  

m↑  The net result is that frequency is decreased.

 

The extrinsic muscles of the larynx have at best a secondary role in frequency change. Professional singers do lower their larynx, which opens the lower pharyngeal cavity for what is called "singer's formant."

 

Now that you have learned about frequency, take a short quiz to test your knowledge. The last question is a challenge question.

 Show quiz group

 

 

Loudness

 Loudness, like pitch, is a perceptual attribute. In acoustics, loudness is measured in intensity or sound pressure level. Physiologically, loudness corresponds to subglottal pressure. Changes in loudness are proportional to changes in subglottal pressure.

 

One way to increase subglottal pressure is with respiratory activity. Specifically,increase in expiratory muscle force. If you start with a larger lung volume by inhaling more air, you get larger relaxation pressures and you don't have to work so hard with the expiratory muscles.

 

A second way to increase subglottal pressure is with laryngeal activity. You can increase adductory muscle force and close the glottis more tightly. Trained singers can do this. For loudness, the vocalis muscle is very important, especially at high frequencies. If you are a nonsinger, you have to rely on other muscle activity. The lateral cricoarytenoid muscle and interarytenoid muscles (both transverse and oblique) can hold the arytenoids more tightly in the back. These muscles are not used as often as the vocalis to make glottal adjustments.

 

The Relationship between Loudness and Frequency

glottalwaveform.png The image on the left is a glottal waveform, which represents the acoustic output of the larynx. The diagram is modifed from this website. The left side of the arc represents lateral movement of the vocal folds as they open. You can see that the more they open, the higher the volume of air that moves through the vocal folds. The right side of the arc is the medial movement, made as the vocal folds start to close. At the end of the medial movement, the vocal folds are closed and there is no air moving through the larynx.

The open time is the time that the vocal folds are open. In this diagram, the open time is the time of lateral and medial movement. Here, it is 4 + 3 = 7. The numbers here are in milliseconds (ms), so the open time is 7. We can see from the diagram that the vocal folds come back faster to the midline than they came apart. It took 4 ms for the vocal folds to become completely open, and 3 ms for them to close.

The T at the bottom of the picture represents the Total period, or complete cycle, of vocal fold movement. It includes the open quotient plus the time the folds are completely closed. Here, the Total period is 3 + 4 + 3 = 10 ms.

The open quotient (OQ) is a ratio expressed by the time the glottis is open divided by the total cycle. Here, the OQ is 7/10, or .7. This means the glottis is open 70% of the time of the entire cycle.

There is another relationship here, too, called the speed quotient. The speed quotient (SQ) is the time of abduction or lateral excursion of the vocal folds over the time of adduction or medial excursion, Here, SQ = 4/3. The speed quotient gives us information about the vibratory characteristics of the vocal folds.

 

You can see more pictures of glottal waveforms in your textbook, on page 84, figure 4.20. Look at the first picture in that figure and take the following quiz. The quiz is a matching quiz--match the numbers 1, 2, and 3 on the figure to what they actually represent.

 Show quiz question

Pitch and loudness tend to co-vary. That means that when pitch increases, loudness increases. It is easier to sing a high note loudly than softly because of the common factors of subglottal pressure: the influences of the larynx and the lungs. When subglottal pressure increases, pitch increases. When subglottal pressure increases, loudness increases. Pitch is primarily affected by laryngeal changes and secondarily affected by respiratory changes. Loudness is primarily affected by respiratory changes and secondarily affected by laryngeal changes.

We also know that if someone is phonating and is punched in the stomach, both loudness and pitch increase. Pitch increases because of two factors: 1) the reflexive tensing of the vocal folds, and 2) the increase in subglottal air pressure, which causes the vocal folds to adduct more quickly as a result of the heightened Bernouilli effect.

The increased vocal intensity results from a greater resistance by the vocal folds to increased airflow. The vocal folds are blown wider apart, releasing a larger puff of air that sets up a sound pressure wave of greater amplitude. The vocal folds are moving farther apart, but they also stay adducted for a larger part of the cycle.

You can see this graphically depicted if you look again at page 84, figure 4.20. The frequency in the bottom figure is greater, reprented by a greater number of peaks, and the peaks are higher. The height of the peaks represents intensity.

 

 Now that you have learned about loudness, take the following quiz.

 

 Show quiz group

 

Vocal Quality

So far we have been looking at pitch and loudness. Now we'll take a look at vocal quality. As a review, from the diagram below, you can see the perceptual, acoustic, and physiologic attributes of pitch, loudness, and quality.

 

Voice Characteristics

Perceptual Attribute

Acoustic Correlate

Primary Physiologic Correlate

Pitch

Fundamental Frequency

Rate of Vocal Fold Vibration

Loudness

Intensity or Sound Pressure Level

Subglottal Pressure

Quality

Spectral Distribution

Mode of Vocal Fold Vibration

 

Voice quality is a perceptual construct, studied in the realm of voice disorders. It is acoustically measured by spectral distribution, and has to do with the synchrony of vocal fold movement. We can look at spectral distribution by looking at a few graphs in the figure below, which are various ways to produce the sound [a].

tau.jpg In this figure, T represents tau, which is the period of a wave form which is repeated. If the period are fairly steady or regular, we get a smooth-sounding voice. If the periods are exactly the same, we get a computerized voice. Looking at the figure, you can see several types of voices.

 

Breathy: This voice has lost the richess of the waveform. The vocal folds are probably vibrating, but are not making good contact. The breathy voice looks like the glottal, or triangular waveform. The air flowing between the vocal folds is turbulent and noisy.

 

Laryngealized: This would be a harsh or rough voice. T2 is slightly longer than T1 . A rough or hoarse voice can be the first indication of a voice problem. The vocal folds are vibrating in a less periodic way, and this adds noise to the signal, which is perceived as hoarseness or roughness

 

Whispered: Thre is no voicing here, so there is no periodicity. Basically, the vocal folds are staying away from each other in the midline. This shape is a noise.

 

Pulsated: This shape is a glottal fry, which sounds like this.

The closure of the vocal folds is loose, air bubbles up throught the glottis, and the sound of the voice is gravely.

 

Voiceless: The voicess graph really looks like silence. If it were truly voiceless, there would be some wiggles in the line, as sound is produced.

 

Here are some more terms associated with voice quality:

 

Jitter vs. shimmer. Jitter is cycle-to-cycle perturbations in frequency, and shimmer is cycle-to-cylce perturbations in amplitude. We know that the larygealized voice in the figure on the left is harsh or rough. The differences betweeen T1 and T2 is jitter--cycle-to-cycle fluctuations in frequency. For a smooth voice, you don't want too much jitter or shimmer. You want frequency and amplitudes to be similar peak to peak.

 

 

Vibrato is a singing voice, a change in frequency.  This is a controlled or purposeful variation in frequency and usually intensity.  It is usually at a rate of 5 Hz, which means 5 times per second. For example, if [a] is said, the cycles are constant in amplitude and frequency.  But if it is sung, we can look at hundreds of these cycles and see a waxing and waning of cycles.  With vibrato, an increase and decrease in the cycles would occur at about 5 times per second.

 

Tremor: We see this in a neurologic impairment or in an older voice.  Unlike vibrato, tremor is NOT controlled, and NOT purposeful, and has to do with the characteristics of the nervous system.  It is a bit faster than vibrato—about 8 Hz.  So, over 100 cycles, see the waxing and waning at about 8 Hz.

 

For vocal quality, the synchrony of the vocal folds is important. If one vocal fold is paralyzed, for examle, the voice will be breathy.  The non-paralyzed fold CAN cross the midline to some degree, and it is common for a paralyzed fold to be somewhere in the middle.  You also get asynchrony if there is a tumor in one of the vocal folds.

 

The tightness of vocal fold adduction 

We also need to consider the tightness of the adduction for vocal quality.  Tightness is on a continuum.  During a whistle, there is no oscillation—no vibration of the vocal folds.  During quiet breathing, the vocal folds are far apart, so there is no sound.  A phenomonon called stridor is seen in infants. The vocal folds are too close together, and you can hear the infant breathe.  Stridor is a noisy turbulence.  This is in contrast to a a whisper, where there is no voicing.  The vocal folds are staying away from each other in the midline.  This shape is a noise. It has no fundamental frequency, no harmonic structure, and can't be easily inflected.  Whispering is not an efficient way to use the breath supply.  We can phonate for 30 seconds but we can whisper for only 10 seconds before having to take a breath.

 

Two terms are used to designate the tightness of vocal fold adduction. In a normal voice,the vocal folds come together, but not excessively, so there is not a lot of strain on the vocal folds.

With hypoadduction, we get a breathy voice. As you recall, during a breathy voice, the vocal folds are probably vibrating, but not making good contact.  We don't get a rich waveform, and it looks a little like the triangular glottal waveform.  The air flowing between the folds is turbulent and noisy. 

 

With hyperadduction, the folds come together very tightly, and we get a strained voice.  In the disorder spasmodic ( or spastic) dysphonia, there is 0 airflow when the vocal folds are adducted.  On occasions, a glottal stop will be produced.  The /o/ in "owe" starts with a glottal stop.  But in /ho/, the glottis is open and the folds gradually start vibrating as they come together.  If there is too much adduction, one technique in therapy is to have clients start words with /h/.

 

Now that you've learned about various voices, take a short quiz about glottal size.

 

 

 

 

Examining other languages for a look at laryngeal activity

The Tuva of central Asia have a style of singing that involves the false vocal folds as well as the true vocal folds. Their singing has more than one fundamental frequency. You can watch a 1-minute video of this here. 

 

Another way to find out how laryngeal activity in speech works is by looking at tone languages. In English, pitch and intonation affect pragmatics, but in Mandarin Chinese, these are phonemic. In English, pitch is non-phonemic, and is used in suprasegmental features like intonation and prosody. Intonation and prosody don't affect the identity of the phonemes, but they can affect meaning. An example is the phrase "You will go" with different intonations. Pitch carries information about the speaker, rather than the content of what the speaker says. You can see the emotional status of the speaker through pitch.

In Mandarin, the different levels of pitch are phonemic. For example, the syllable "ma" said with a high tone is "mother." Say the syllable with a high rising tone, and you have "hemp." Say the syllable with a low dipping tone and you have "horse." Finally, say it with a high falling tone and it means "to scold."

 

Clinical correlations

Measuring laryngeal function

One way to visualize the larynx is with an instrument called an endoscope. The endoscope may be rigid or flexible. The rigid endoscope may be uncomfortable for the patient, and may elicit the gag reflex. Since the scope is inserted through the mouth, the patient is limited to sustained vowel sounds, rather than speech. The flexible endoscope is inserted through the nasal passage for an unobstructed view of the vocal folds. Since the scope does not interfere with pharyngeal movement, the larynx can be visualized producing a wide variety of speech.

 

The electroglottograph is an inexpensive, simple machine that measures the amount of contact between the vocal folds as they are vibrating. Electroglottography is a non-invasive procedure, and two electrodes are placed on the neck over the thyroid cartilage. The degree of vocal fold approximation and fundamental frequency are two of the measures which can be obtained through electroglottography.

 

The voice can also be measured acoustically, through instruments such as the Computerized Speech Lab (CSL) by Kay-Pentax. The CSLcaptures the voice and can measure sound pressure level, frequency, and time. It will display the voice in a waveform and in a spectogram, and measure jitter, and shimmer, among other parameters. The CSL is probably the gold standard for clinical analysis of speech and for research, but there are some very good downloadable free programs which also perform voice analysis. Two of the more popular ones are CSpeech/TF32 and Praat. The lab for this unit involves making some acoustic measures of voice through a free downloadable program called Praat.

 

The role of the speech-language pathologist in working with laryngeal disorders

Voice disorders may occur through vocal abuse, or may be of an organic nature, for examples tumors or cysts. They may also occur as a part of a neurological disorder, such as Parkinson's disease, or through trauma. Speech-language pathologists assess and treat voice disorders. They may provide therapy and instruction on the proper use of the voice, and/or use instrumentation to diagnose and treat a voice disorder.

 

Summary Page

Now that you have finished his module, I hope you have a better understanding of phonation.  As a review, after studying this unit, you should be able to:

1. relate how the anatomy and physiology of the larynx, coupled with respiration, enables phonation.

2. describe the Bernouilli effect and the myoelastic aerodynamic theory as they pertain to vocalization.

3. relate how vocal fold vibration is related to frequency, and the factors that increase and decrease frequency.

.4. describe what voice intensity is how it relates to frequency.

5. describe what factors play a role in vocal quality.

.6. assess ways to measure laryngeal function an

7. analyze phonation using Praat.