Respiration + Vocal Fold Physiology

Feburary 6, 2014

Average Everydayness• Production exercise #1 is due today!

• I’m hoping to start grading it (and the DSP exercise) tonight.

• There will be a second production exercise, due before the break.

• Course project report #2 is due on Tuesday!

• Today:

• The Wonderful World of the Larynx!

From the Bottom Up• All speech sounds require airflow.

• The vast majority of sounds in the world’s languages use a pulmonic egressive airflow.

• = out of the lungs

• Questions to answer/consider:

1. How do we make air flow out of the lungs?

2. How does pulmonic airflow differ in breathing and in speech?

3. How does pulmonic airflow relate to language?

• primarily: suprasegmentals (stress, F0)

The Machinery• The human torso (from

the neck to the legs) has two major divisions:

1. The thorax

• consisting of the heart and lungs

• the “chest”

2. The abdomen

• includes the digestive system and other interesting glands

• the “belly”

The Thorax• The heart and the pulmonary system are enclosed by the thoracic cage.

• the “rib cage”

• Ribs are connected by cartilage to the sternum.

• The intercostal muscles fill in the gaps between ribs...

• and also cover the surfaces of the thoracic cage.

Connections• The thorax is split from the

abdomen by a dome-shaped structure known as the diaphragm.

• The lungs sit on top of the diaphragm.

• Two membranes link the lungs to the ribs:

1. The visceral pleura covers the lungs.

2. The parietal pleura lines the inside of the thoracic cage.

Equilibrium

volume

• The linkage between the lungs and the rib cage makes:

• The lungs are bigger than they would be on their own.

• The rib cage is smaller than it would be on its own.

• The linkage tends towards a natural equilibrium point.

Taking A Step Back• Air flows naturally from areas of high pressure to areas of low pressure.

• Q: How do we make air pressure differences?

• A: We take advantage of Boyle’s Law.

• Boyle’s Law states that:

• the pressure of the gas in a chamber is inversely proportional to the volume of gas in the chamber

• The pressure of the gas can be increased or decreased by changing the volume of the chamber.

• decreasing volume increases pressure

• increasing volume decreases pressure

Inspiration• A normal breathing cycle begins with inspiration

• “breathing in”

• Air will flow into the lungs if...

• the air pressure inside the lungs is lower than it is outside the lungs

• Air pressure can be decreased inside the lungs by...

• expanding the volume of the lungs.

• Lung volume can be expanded:

• In all three dimensions

• With two primary muscle mechanisms

Expansion #1• The vertical expansion of the thorax is primarily driven by the contraction of the muscles in the diaphragm.

• This bows out the front wall of the abdomen.

• Also: diaphragm contraction elevates the lower ribs.

• expands the circumference of the thorax.

Expansion #2• The thorax can also be expanded through the contraction of the external intercostal muscles.

• Contraction of each intercostal muscle lifts up the rib beneath it.

• Also pulls each rib forward with the sternum.

• = expansion in the front-back dimension.

sternum

Expansion #3• The thorax can also be expanded through the contraction of the external intercostal muscles.

• Contraction of the intercostals elevates the lower ribs more than the upper ribs

• Lower ribs lift like a “bucket handle”

• Expansion in the side-to-side dimension.

Expiration• Air flows out of the lungs whenever air pressure in the lungs is greater than external air pressure.

• Note: technical term

• alveolar pressure = air pressure inside the lungs

• Alveolar pressure may be increased by decreasing lung volume.

• Lung volume is decreased through both passive and active forces.

• Normally, lungs contract after inspiration due to passive forces alone.

• No muscular effort is necessary!

Passive Expiration• Thorax + lungs combo contracts back to its equilibrium point without any external impetus.

• Relaxation pressure is inherent pressure on the lungs to revert back to the equilibrium point.

• Note: relaxation pressure works both ways.

Active Expiration• Lung volume can be actively decreased by contracting

a variety of muscles which:

1. Lower the ribs and/or sternum

• thereby compressing the thorax in the front-to-back and side-to-side dimensions

2. Increase abdominal pressure

• thereby driving the diaphragm upwards

Expiration #1• The thoracic cage can be compressed by contracting the internal intercostals and the transversus thoracis.

• These pull the ribs downward...

• effectively the opposite action of contracting the external intercostals.

Expiration #2• The most important muscles for active expiration increase pressure in the abdomen.

• These include the rectus abdominis, the external and internal obliques, and the transversus abdominis.

• Contracting these muscles drives in the abdomen...

• and pulls down the sternum and lower ribs.

Expiration Dynamics• Technical term: the equilibrium point of thorax + lung volume is called the resting expiratory level.

• At volumes above the resting expiratory level, the lungs will contract due to relaxation pressure alone.

• ...although active expiration forces may contribute.

• Below the resting expiratory level, the lungs will tend to expand due to relaxation pressure.

• To continue expiration at this level, active expiration is necessary.

More Verbiage1. Total lung capacity: volume of air in the lungs after a

maximum inspiration.

2. Residual volume: amount of air that remains in the lungs after a maximum expiration.

3. Vital capacity: greatest amount of air that can be expelled from the lungs after a maximum inspiration.

• = total lung capacity - residual volume

4. Functional residual capacity: volume of air contained in the lungs at the resting expiratory level.

5. Inspiratory capacity: maximum volume of air that can be inspired from the resting expiratory level.

• = total lung capacity - functional residual capacity

Verbiage Diagram #1

residual volume

total lung

capacity vital capacity

Verbiage Diagram #2

functional residual capacity

inspiratory capacity

total lung

capacity

Note: FRC - RV only 35% of vital capacity

Keeping it Steady• The production of speech generally requires a continuous flow of air from the lungs.

• A continuous flow of air requires constant alveolar pressure in the lungs.

• Accomplishing this is tricky...

• Because there is more relaxation pressure at the extremes (both high and low) of lung capacity.

• Active inspiratory and expiratory forces have to dynamically compensate.

external air pressure

constant pressure needed for utterance

• Relaxation pressure changes from expiratory to inspiratory...

• in going from maximum to minimum vital capacity

expiratory pressure

inspiratory pressure

Effort required to maintain constant alveolar pressure:

effort initially requires inspiratory forces!

effort eventually requires expiratory forces

active inspiratory pressure

active expiratory pressure

Electromyography (EMG)• The activity of inspiratory and expiratory muscles during continuous exhalation has been documented with electromyography (EMG) studies.

• In EMG, an electrode is inserted into a particular muscle.

• When that muscle contracts, it discharges an electrical signal (an action potential).

• The voltage and timing of this discharge may be recorded through the electrode.

EMG Recordings

Diaphragm

External Intercostals

Internal Intercostals

Rectus Abdominis

External Oblique

Latissimus Dorsi

inspiratory

expiratory

• The intensity of an utterance is primarily determined by alveolar pressure.

• Doubling alveolar pressure increases intensity by 9 -12 dB.

Loudness

• Louder utterances require a greater difference between alveolar and external air pressures

• Louder utterances require more active expiratory force.

Differences• Conversational speech makes different demands on the respiratory system than either normal breathing or the production of a continuous vowel.

• For instance, a normal breath cycle lasts about five seconds:

• 40% of the cycle is devoted to inspiration

• 60% of the cycle is devoted to expiration

• In speech:

• 10% of the cycle is devoted to inspiration

• 90% of the cycle is devoted to expiration (i.e., talking)

Volume Differences• Normal breathing encompasses 35% - 45% of vital capacity.

• Note: normally ends above the resting expiratory level.

• Normal conversational speech encompasses 35% - 60% of vital capacity.

• Loud speech usually starts at 60% - 80% of vital capacity.

• and may end considerably above resting expiratory level.

• Note: extremes of the vital capacity are not normally used, in either breathing or speech.

• (requires too much muscular effort)

Modulating Airflow• During conversational speech, there are frequent demands for rapid changes in muscular pressure.

• These changes are primarily required for differentiating between stressed and unstressed syllables.

• Rapid modulations to airflow are primarily made by the internal intercostal muscles.

Lastly• Higher airflow from lungs = increase in F0

• The have-your-friend-punch-you-in-the-stomach experiment.

• Increased F0 also contributes to stress.

• However, F0 level is primarily determined by laryngeal activity...

• which we’ll talk about next...

Where Were We?• Air squeezed out of the lungs travels up the bronchi...

• Through the trachea (windpipe)

• To a complicated structure called the larynx.

• ...where phonation happens.

The Larynx• The larynx is a complex structure consisting of muscles, ligaments and three primary cartilages.

1. The Cricoid Cartilage• The cricoid cartilage sits on top of the trachea

• from Greek krikos “ring”

• It has “facets” which connect it to the thyroid and arytenoid cartilages.

cricoid cartilage

2. The Thyroid Cartilage• The thyroid cartilage sits on top of the cricoid cartilage.

• from the Greek thyreos “shield”

• The thyroid cartilage has horns!

• Both lower (inferior) and upper (superior) horns

• The lower horns connect with the cricoid cartilage at the cricoid’s lower facet.

• The upper horns connect to the hyoid bone.

Thyroid Graphic

thyroid cartilage

cricoid cartilage

Thyroid Angles• The two broad, flat front plates of the thyroid--the laminae--meet at the thyroid angle.

• The actual angle of the thyroid angle is more obtuse in women.

• ...so the “Adam’s Apple” juts out more in men.

3. The Arytenoid Cartilages• There are two arytenoid cartilages.

• from Greek arytaina, “ladle”

• They are small and pointy, and sit on top of the back side, or lamina, of the cricoid cartilage.

arytenoid cartilages

cricoid cartilage

The Vocal Folds• These three cartilages are connected by a variety of muscles and ligaments.

• The most important of these are the vocal folds.

• They live at the very top of the trachea, in between the cricoid and thyroid cartilages.

• The vocal folds are a combination of:

• The vocalis muscle

• The vocal ligament

• The vocal folds are enclosed in a membrane called the conus elasticus.

• Just above the true vocal folds are the “false” (!) vocal folds, or ventricular folds.

• The space between the vocal folds is the glottis.

Vocal Fold View #1

Vocal Fold View #2• The vocal ligaments attach in the front to the thyroid cartilage.

• ...and in the back to the arytenoid cartilages.

• The glottis consists of:

• the ligamental glottis

• the cartilaginous glottis

Things Start to Happen• Note that the arytenoid cartilages can be moved with respect to the cricoid cartilage in two ways.

#1: rocking #2: sliding

The Upshot• The arytenoids can thus be brought together towards the midline of the body.

• Or brought forwards, towards the front of the thyroid.

• The rocking motion thus abducts or adducts the glottis.

• The sliding motion shortens or lengthens the vocal folds.• Check out the arytenoids in action.

• When the vocal folds are abducted:

• air passes through the glottis unimpeded and voicelessness results.

• The posterior cricoarytenoid muscles are primarily responsible for separating the arytenoid cartilages.

• Voicing may occur when the vocal folds are adducted and air is flowing up through the trachea from the lungs.

• Two muscles are primarily responsible for adducting the vocal folds.

• The first is the lateral crico-arytenoid muscle.

• Note that the lateral cricoarytenoid muscles only adduct the ligamental glottis.

• The transverse arytenoid muscles pull together the arytenoid cartilages themselves.

• Thereby closing the cartilaginous glottis.

The Consequences• The combined forces drawing the vocal folds towards each other produce adductive tension in the glottis.

• Adductive tension is increased by:

• lateral cricoarytenoid muscles

• transverse arytenoid muscles

• Adductive tension is decreased by:

• posterior cricoarytenoid muscles

• Adduction vs. abduction determines whether or not voicing will occur.

• But we can do more than just adduce or abduce the vocal folds...

Controlling F0• Question: why do women have a higher F0 than men?

• A: Shorter vocal folds open and close more quickly.

• In men:

• Ligamental glottis 15.5 mm

• Cartilaginous glottis 7.5 mm

• Total glottis length 23 mm

• In women:

• Ligamental glottis 11.5 mm

• Cartilaginous glottis 5.5 mm

• Total glottis length 17 mm

Factor Two

• F0 also depends on the longitudinal tension in the vocal folds.

• I.e., tension along their length, between the thyroid and arytenoid cartilages.

• Higher tension = higher F0

• Lower tension = lower F0

• Q: How can we change longitudinal tension in the larynx?

• A: We can rotate the thyroid cartilage up and down on its connection with the cricoid cartilage.

• ...like the visor of a knight’s helmet.

• This either stretches or relaxes the vocal folds.

Contradictory?• No, just complicated. Note:

• Lengthening (stretching) the folds results in higher tension

• ...which results in higher F0

• Shortening the folds results in less tension

• ...which results in lower F0

• “Higher” and “lower” F0 have to be understood relative to the speaker’s normal F0 range.

• still lower for men

• still higher for women

For the Record• Contraction of the cricothyroid muscle pulls down the thyroid cartilage.

• Interestingly: researchers often study the activity of this muscle using EMG.

Fun Stuff (= tracheotomy)Peter Ladefoged: “To record the pressure of the air associated with stressed as opposed to unstressed syllables we need to record the pressure below the vocal folds. A true recording of the subglottal pressure can be made only by making a tracheal puncture.This is a procedure that must be performed by a physician. A local anesthetic is applied both externally and inside the trachea by means of a fine needle. A larger needle with an internal diameter of 2 mm can then be inserted between the rings of the trachea as shown in figure 3.3”

Figure 3.3

“As you can see from my face it is not at all painful. But it is not a procedure that can be carried out in fieldwork situations.”

For the Record, part 2• Longitudinal tension can also be reduced by the thyroarytenoid muscles.

• Which connect the thyroid to the arytenoid cartilages.

vocal folds

• These muscles are inaccessible to EMG

Check it out!• Let’s look at some pitch shifting laryngoscopy videos.

Factor #3• Increasing longitudinal tension also makes the vocal folds thinner.

• Thinner vocal folds open and close more quickly.

• Average thickness of male vocal folds =

• 2-5 mm

• Female folds are somewhat thinner

low F0

mid F0

high F0

Frequency and Vowels• In the mystery tone language exercise, you may have noticed that the fundamental frequency of [i] was slightly higher than that of [a], for the same tones

“Intrinsic” Pitch• It’s been observed that F0 is usually higher for high vowels than for low vowels

[i] 183 Hz

[e] 169

[æ] 162

[a] 163

[o] 170

[u] 182

• Data from Lehiste & Peterson (1961) for American English

• The “Tongue Pull” Hypothesis (Honda, 2004):

• Raising the tongue for high vowels also raises the larynx

• The cricoid cartilage rises up and around the spine…

• Thus stretching the vocal folds

• and increasing longitudinal tension.

An Intrinsic Summary High Vowels Low Vowels

Intensity Less More

Duration Shorter Longer

F0 Higher Lower

• A word of caution:

• All of these factors (intensity, duration, F0) factor into perceived prominence and stress.

Contact!• Interesting (and important) fact: the vocal folds do not open and close all at once.

• Their upper and lower parts open and close out of phase with each other.

Implications• Glottal opening and closing forms a complex wave.

• The out-of-phase factor is reduced with thinner vocal folds.

• i.e., the glottal cycle becomes more sinusoidal

Electroglottography• The degree of vocal fold separation during voicing can be measured with a method known as electroglottography (EGG)

• Electrodes are placed on either side of the larynx

• More contact between vocal folds greater conductivity between electrodes

• A caveat:

• tends to work better on men than women.

EGG Readout

EGG Output

“The north wind and the sun were disputing which was the stronger, when a traveler came along wrapped in a warm cloak.”

An EGG Schematic1. Complete closure of vocal folds

conductivity

An EGG Schematic2. Lower half of folds begin to open

conductivity

An EGG Schematic3. Upper half of folds open

conductivity

An EGG Schematic4. Folds are completely apart

conductivity

An EGG Schematic5. Lower half of folds begin to close

conductivity

An EGG Schematic6. Upper half of folds close

conductivity

An EGG Schematic7. Folds are completely closed, again

conductivity

An Actual EGG Waveform• Modal voicing (by me):

• Note: completely closed and completely open phases are both actually quite short.

• Also: closure slope is greater than opening slope.

• Q: Why might there be differences in slope?

Factor #5• There is another force at work: medial compression.

• i.e., how tightly the folds themselves are compressed against each other.

• Medial compression determines, to some extent, how quickly/slowly the folds will open.

MC Forces, yo• Medial compression is caused by constriction of:

1. The lateral cricoarytenoids

• which adduct the vocal folds

2. The thyroarytenoids

• which pull the arytenoids towards the thyroid

• But not the interarytenoids

• ...which only squeeze the arytenoid cartilages together

For the Record, part 3• It is not entirely clear what the role of the vocalis

muscle plays in all this.

• The vocalis muscle is inside the vocal folds

The Vocalis Muscle1. It may also shorten the vocal folds through contraction

• thereby potentially lowering longitudinal tension

• and lowering F0

2. However, the same contraction would increase medial compression within the vocal fold

• thereby decreasing vocal fold thickness

• and increasing F0

• Researchers still need to figure out a way to get at this muscle while it’s in action…

Vocal Fold Force Summary1. Adductive Tension

• between arytenoids + folds

2. Longitudinal Tension

• stretches vocal folds

3. Medial Compression

• squeezes vocal folds together

1. Modal Voice Settings• At the low end of a speaker’s F0 range:

1. Adductive tension force is moderate

2. Medial compression force is moderate

3. Vocal folds are short and thick.

• = longitudinal tension is low

4. Moderate airflow

• F0 is increased by:

1. Increasing the longitudinal tension

activity of the cricothyroid muscle

2. Increasing airflow

A Different Kind of Voicing• Tuvan throat singing (khoomei):

A Different Kind of Voicing• The basic voice quality in khoomei is called xorekteer.

• Notice any differences in the EGG waveforms?

• This voice quality requires greater medial compression of the vocal folds.

• ...and also greater airflow

• Check out the tense voice video.

Modal vs. Tense Voice• The language of Mpi contrasts modal voice vowels with tense voice vowels.

• Mpi is spoken in northern Thailand.

Taken to an Extreme• Extreme medial compression can lead to the closure of the ventricular folds, as well as that of the true vocal folds.

• = ventricular voice

• The false and true vocal folds effectively combine as one.

• …and open and close together (usually)

• Kargyraa voice

• Head over to the video evidence.

Ventricular Voice EGG

• Notice any differences?

• Difference between closing and opening slope is huge!

• Also: amplitude is larger.

2. Creaky Voice• A voice quality that is somewhat similar to ventricular

voice is creaky voice.

• Also known as “glottal fry”

• Laryngeal settings for creaky voice:

1. Ventricular folds often compressed down on true vocal folds.

2. High medial compression

3. Very little longitudinal tension

4. Low airflow

• Air bubbles up sporadically through the folds, near the thyroid arch.

Creaky EGG

• Note: vocal folds are very short during creaky voicing.

• Look at the creaky video.

Creaky Quirks• Note: creaky voice often emerges at the low end of a speaker’s range.

• In a language like English, at the ends of utterances

• In a tone language, for very low tones.

• Note: creaky voice also often has a “double pulse” effect.

Modal to Creaky

[ ]

Jitter• Creaky voice often exhibits a lot of jitter and shimmer.

• Jitter =

• Variation in timing of glottal pulses

• Defined as a percentage:

• period deviation/period duration.

Shimmer• Shimmer =

• Variation in amplitude of glottal pulses

• Note: synthetic speech has to include jitter and shimmer

• …otherwise the voice won’t sound natural.

• Check the measures out in Praat.

3. Breathy Voice• In breathy voice, the vocal folds remain open…

• and “wave” in the airflow coming up from the lungs.

• Laryngeal settings for breathy voice:

1. Low medial compression

2. Minimal adductive tension

3. Variable longitudinal tension (for F0 control)

4. Higher airflow

• Check out the breathy video.

Breathy Voice EGG

• Also note: closure phases in breathy voice are more symmetrical than in modal voice.

Some Real-Life Examples

breathy

modal

Contrasts• Gujarati contrasts breathy voiced vowels with modal voiced vowels:

• Hausa contrasts modal [j] with creaky [j]:

• Hausa is spoken in West Africa (primarily in Nigeria)

• Creaky consonants are also said to be laryngealized.

All Three• Jalapa Mazatec has a three-way contrast between modal, breathy and creaky voiced vowels:

• Jalapa Mazatec is spoken in southern Mexico, around Oaxaca and Veracruz.

Voiced Aspirated• Some languages distinguish between (breathy) voiced aspirated and voiceless aspirated stops and affricates.

• Check out Hindi:

One Random Thing• Breathy voiced segments can “depress” the tone on a following segment.

• Examples from Tsonga:• Tsonga is spoken in South Africa and Mozambique.

• Voiced stops also “depress” tones more than voiceless stops.

• depressor consonants

• Nobody really knows why.

Open Quotient• From EGG measures, we can calculate the “open quotient” for any particular voicing cycle =

time glottis is open

period of voicing cycle

• EGG measures show that there are reliable differences in open quotient values between the three primary voicing types.

• Breathy voicing has a high open quotient

• Creaky voicing has a low open quotient

• Modal voicing is in between

Open Quotient Traces

one period

open phase

• The open quotient in modal voicing is generally around 0.5

Tense Voice

• Tense voice (from throat singing demo) has a lower open quotient.

• Result of medial compression.

• Actual value: about 0.3

one period open phase

OQ Traces, continued

• OQ for creaky voice is also supposed to be low…

• but it’s actually quite sporadic.

• Breathy voice OQ is quite high

• (0.65 or greater)

4. Whispery Voice• When we whisper:

• The cartilaginous glottis remains open, but the ligamental glottis is closed.

• Air flow through opening with a “hiss”

• The laryngeal settings:

1. Little or no adductive tension

2. Moderate to high medial compression

3. Moderate airflow

4. Longitudinal tension is irrelevant…

Nodules• One of the more common voice disorders is the development of nodules on either or both of the vocal folds.

• nodule = callous-like bump

• What effect might this have on voice quality?

Last but not least• What’s going on here?

• At some point, my voice changes from modal to falsetto.

5. Falsetto• The laryngeal specifications for falsetto:

1. High longitudinal tension

2. High adductive tension

3. High medial compression

• Contraction of thyroarytenoids

4. Lower airflow than in modal voicing

• The results:

• Very high F0.

• Very thin area of contact between vocal folds.

• Air often escapes through the vocal folds.

Falsetto EGG

• The falsetto voice waveform is considerably more sinusoidal than modal voice.

Voice Quality SummaryAT LT MC Flow

Modal moderate varies moderate med.

Tense high varies high high

Creaky high low high low

Whisper low N/A high med.

Breathy low varies low high

Falsetto high high high low