Among the creatures of earth, only humans have achieved speech. All species of animals communicate, many through vocalizations, but none have approached the complexity and sophistication of our oral language. Yet the body parts we use to produce speech do not appear to be vastly different from those of other animals that also have teeth, tongues, and palates. Like other species, we use these oral structures regularly for basic biological functions such as breathing and eating. However, we know that a healthy human infant has an innate potential to communicate orally. Research tells us that humans have some unique neurological and structural characteristics that allow us to use these body parts for speech production in addition to their basic, vegetative function.
Speech is actually the end product of four processes or actions that occur simultaneously and cooperatively: ,phonation, resonation, and articulation. It is very important to understand the implications of the terms simultaneously and cooperatively .Speaking is not a linear sequence of events that begins with the lugs and ends with the listener’s ear. The act of speaking requires continuous. overlaping action as well as feedback adjustments across all the systems involved. In order to understand the speech processes, we begin with a description of the basic structures involved in speech production.
THE SPEECH MECHANISM:SUPRAGLOTTAL STRUCTURES
As we review the structures of the speech mechanism, we will cover vegetative(biological) function, speech functions, and terms commonly associated with each structure. Although we will discuss the structures of the speech mechanism separately, remember that all these structures function synergistically to produce speech. To emphasize the interaction, we have grouped the structures according to location and function.
THE SUPRALARYNGEAL STRUCTURES
The supralaryngeal structures refer to those parts of the speech mechanism located above the level of the larynx. Each of these structures is contained in one of three cavities or spaces: oral, nasal, or pharyngeal. The pharyngeal cavity, or pharynx, extends from the opening of the larynx to the posterior boundaries of the oral cavity (mouth) and nasal cavity (nose) (see Figure 2-1).Positioning and movements of the structures in these cavities shape the outgoing airstream into the vowels and consonants we recognize as speech.
ORAL CAVITY
The lips are the external boundary of the oral cavity. They are actually a complex of muscles and other tissues. For vegetative functions, they help receive and contain food and fluids in the oral cavity. In speech, they perform a variety of actions. For vowels, position can range from rounded to neutral to spread. These changes in shape contribute to the resonant pattern that characterizes different vowels. Several consonants are classified as labial(involving the lips).Some of these consonants are bilabial(both lips used),such as/b/,and others are labiodental (lip and teeth used),such as/v/.In most speakers,the lower lip is more mobile in rapid, connected speech.
TEETH
The role of the teeth for live support is an abvious one : cutting and grinding food. There speech role is primarily passive but nonetheless important. In English, two consonants are classified as dental or inter dental ( involving the teeth ): the /0/ in thorn and the /0/ in them. However, production of a number of consonant such as /s/ and /z/ requires that the back sides of the tongue be sealed against the back teeth (molar)to direct the airstream appropriately. Otherwise, air may escape laterally, resulting in a distortion of the sound (s). loss of the central incisors (front teeth) between ages 5 and 7 results in many children having a lips (/s/) problem. The problem disappears when the permanent incisors grow in fully
ALVEOLAR RIDGE
In both the maxilla (upper jaw) and mandible (lower jaw), the teeth are contained in the alveolar ridge (alveolar processes, more commonly known as the “gum ridge”). Biologycally, the alveolar ridge serves as an important surface for tongue contact in the act of swallowing in speech, many consonant involve tongue contact with, or placement near, the upper alveolar ridge, which is found behind the maxillary incisor and cuspid teeth. Alveolar consonants such as /t/, /s/, and /l/ to name just a few, involve the maxillary alveolar ridge. In addition, the alveolar ridge, along with the anterior palate, serves as a “reference point” for the tongue in front vowel formation.
HARD PALATE
The hard palate is composed of bony tissue and covered by the mucous membrane. It divides the oral and nasal cavities, forming the roof of the oral cavity and the floor of the nasal cavity. For life-sustaining purposes, the palate helps contain food in the oral cavity and provides a hard upper surface for swallowing. It is involved in both vowel and consonant production for speech. For vowels, it plays a role in oral cavity shaping. Several consonants are considered palatal : /f/,/3/,/tf/,/0/,/r/, and /j/. All require the tongue to be positioned near, or to move in relation to the palate.
SOFT PALATE
Posterior to the hard palate, the velum or soft palate forms the roof of the mouth. It is composed of muscle and connective tissue and is covered by a continuation of the mucous membrane of the hard palate. Biologically, its action is necessary to prevent foods and fluid from entering the nasal cavity. Opening and closing of the velopharyngeal port(aperture/opening that connects the nasal and oral cavity)require participation of the velum. Its muscular composition makes it highly flexible and important for speech function. By helping to close the velopharyngeal port, the velum helps direct the breath stream to the oral cavity for articulation of oral resonant phonemens, especially vowels. Relaxation of the velum opens the velopharyngeal port and is necessary to produce the three nasal consonant phonemes/m/,/n/,and /0/.Consonants involving tongue contacs with the velum,/k/,/g/,and /0/,are referred to as velar consonants.
TONGUE
The tongue (adjective, lingual-/-lingua)is composed of muscle and connective tissue and covered by the mucous membrane. It is of extreme importance for both biological purposes and speech. Its role in life function is crucial: directing food to the back of the oral cavity in swallowing. Highly flexible and mobile, the tongue can shape the oral cavity almost infinitely. It arises from the floor of the oral cavity and is dually controlled by both intrinsic (within the tongue) and extrinsic(connecting the tongue to other structures)muscles. To understand the specific role of the tongue in vowel and consonant production, you need to be familiar with various tongue landmarks. The tongue itself has a root, apex, dorsum, septum, and frenum. The root is the posterior portion, connecting to the hyoid bone and the epiglottis. The anterior end of the tongue is its apex, and the superior(upper) surface, the dorsum. The lingual septum is actually a midline structure of the connective tissue. The front tongue undersurface is connected to the mandible by the lingual frenum. In describing speech articulation, we refer to various landmarks on the tongue surface: back, middle, front/blade, and tip(see figure 2-2). Consonants such as /s/and /t/ involved the tip, where as /k/ and /g/ involve the back. In producing consonants and vowels, the tongue shape can vary from broad to narrow, flat to curled, and whole tongue positioning to differential positioning of tongue segments. All the vowels and most of the consonants require tongue action. Only /m/, /p/, /b/, /f/, and /v/ do not.
NASAL CAVITY
The nasal cavity lies directly superior to the oral cavity. Horizontally, it extends from the external nares (nostrils) to the posterior pharyngeal wall. Vertically, it is bounded by the base of the skull and the palate and velum. Its primary purpose is to receive inhaled air, filter it, warm it, and direct it toward the trachea (windpipe). With its soft, moist lining, it contributes to the distinctive resonance characteristic of the cavity. The nasal cavity participates in speech resonance with either closure or opening of the velopharyngeal part. It is always open anteriorly, at the nostrils, unless you have a cold or other infection. Even if the velopharyngeal port is closed, the nasal cavity resonates the vibrating airstream from the larynx. In this case, the combined resonation of oral and nasal air produces an individual speaker’s distinctive voice quality. Production of /m/, /n/, and /0/ requires closure somewhere in the oral cavity combined with opening of the velopharyngeal port (lowering the velum). This allows the nasal cavity to serve as the primary resonator.
PHARYNGEAL CAVITY
Anatomically, the pharynx (pharyngeal cavity) extends from posterior portion of the nasal cavity downward past the back of the oral cavity to (but not including) the larynx (see Figure 2-1). Biological function include (1) receiving food from swallowing and moving it toward the esophagus and stomach and (2) channeling air from respiration between the nose and mouth, trachea and lungs. A vertical tube, the pharynx actually can be subdivided into three parts : the nasopharynx (continuation of the nasal cavity), the oropharynx (continuation of the oral cavity), and the laryngopharynx (just above the larynx). For speech production, the pharynx acts as a resonating chamber for the voice. (although some language use the pharynx for consonant articulation, English is not one of them). The primary pharyngeal alteration is velopharyngeal closure that both directs the voice into the oral cavity and reduces the length of the pharyngeal tube (by closing off the nasopharynx). Pharyngeal circumference can also be changed by constricting characteristics of the pharynx and, consequently, the sound of the human voice.
THE LARYNX AND SUBGLOTTAL STRUCTURES
The larynx is composed of cartilage and muscle. It sits on top of, and is connected to, the trachea (see Figure 2-3 A, B). its most crucial life support function is protection of the lungs by preventing food particles and fluids from entering the trachea. Any food materials that enter the larynx are expelled by coughing. Other vegetative functions include closing the trachea so that air is held in he chest (thoracic) cavity. This frees the muscles such as the pectoralis mayor from respiration and allows them to participate in important tasks such as heavy lifting.
The larynx (adjective, laryngo-/-laryngeal)is suspended from the hyoid bone by a complex of muscles and ligaments and ligaments and lies posterior and slightly inferior to the tongue root. It contains the vocal folds necessary for phonation (vocal fold vibration). The vocal folds are actually “shelves” of muscles and connective tissue, lined with mucous membrane. The space between the vocal folds is referred to as the glottis, and sometimes laryngeal structures are referred to as subglottal or supraglottal, depending on their spatial relationship with the vocal fold opening. The vocal folds are anchored to the inner surface of the large thyroid cartilage anteriorly. Posteriorly, the folds attach to the movable arytenoid cartilages. There cartilages allow the vocal folds to be abducted (positionedapart)of adducted (positioned together, or approximated) (see Figure 2-4). Inferiorly, the cricoids cartilage forms the base of the larynx and rests atop the trachea. In summary, then, the structures important to laryngeal function are cricoids cartilage, paired arytenoid cartilages, thyroid cartilage, hyoid bone, and vocal folds.
Phonemes that are produced with vocal fold vibration (vocal folds adducted) are referred to as voiced sounds : those produced with the vocal fold abducted are voiceless. All American English vowels and the majority of consonants are voiced.
Sublaryngeal structure are the organs of respiration that provide the breath stream necessary for speech production (see Figure 2-5). The trachea is immediately below (and attached to) the cricotiroid cartilage. It is actually a tube of cartilaginous rings and other connective tissue that descends in front of the esophagus and bifurcates( divides in half) into two primary bronchi. The paired bronchi enter the lungs and continue to bifurcate into smaller bronchioles. Ultimately, the bronchioles terminate in the alveolar ducts,which lead to the alveolar sacs. The alveoli are contained in the walls of the alveolar sacs and serve as the site for the exchange of oxygen and carbon dioxide. Other sublaryngeal structures necessary for life support and speech include the rib cage, diaphragm, and other muscles of respiration.
SPEECH PROCESSES AND ASSOCIATED STRUCTURES
Now that you are familiar with the structures involved in the speech process, we will discuss their integrated roles in speech production. The resulting, overlapping of respiration, phonation, and articulation together are responsible for the veriety of sounds we use to transmit as oral language. Coordination of these processes requires complex interaction, feedback, and adjustments, mediated by the nervous system (brain, cranial nerves, and spinal cord).
RESPIRATION
Human oral community requires some type of air source for its occurrence. Respiration is accomplished by a complex interaction of respiratory structures and muscles. The structures involved respiration, as we noted earlier, include, the lungs, bronci, bronchioles, alveoli and trachea. The muscles involved in respiration primarily include the diaphragm and the external and internal intercostals muscles (see Figure 2-5). However, respiration for speech requires more than just structures and muscle activity, as you will discover in the next section.
Whether breathing for speech or simply breathing quietly (life support), you inhale (bring air into lungs) and exhale (release air from the lungs). Oxygen and carbon dioxide exchange occurs in the lungs each time you inhale and exhale, whether you speak or not. The exhalation phase of respiration provides the flow of breath for speech.
Inhalation consist of taking air into the lungs. Contraction of the diaphragm causes expansion of the thoracic cavity space. Co-occurring upward and outward rip cage movement due to the action of the thoracic and neck muscles also expands this space. The elastic properties of the lungs allow them to expand. Oxygen and carbon dioxide exchange occurs in the alveoli of the lungs. Exhalation (which provides the egressive, or outgoing, airstream for speech) is achieved by a combination of these factors : (1) gravity (2) elastic properties of cartilage and lung tissue, and (3) relaxation of the muscles of inhalation.
In normal breathing, the relative duration of inhalation and exhalation is about the same. But in speaking, the duration of exhalation in a single respiratory cycle is usually about 10 times longer than that of exhalation. Practiced speakers may actually have their exhalation phase last 50 times longer than inhalation. Despite differences in inhalatory and exhalatory cycle length for life support and speech, the actual amount of air exchanged is about same, regardless of purpose. The extended duration of exhalation for speech reflects extremely efficient control of the breath stream. This efficiency results from the synergistic functioning of the respiratory muscles, larynx, and articulatory system cause adjustments in the exhalation process. This degree of control takes time to master : consider how cry and become out of breath but how a trained singer can easily sustain a note for a long period.
PHONATION
Phonation, or voicing, is accomplished by the interruption of the outgoing airstream by rapid rhythmic closing and opening of the glottis with the vocal folds. The vocal folds are steadily but lightly approximated (together) when the arytenoid cartilages are adducted by muscle action. This degree of closing allows the folds to be parted by accumulated subglottal air pressure coming from the lungs. The folds then reapproximate from the combined effects of muscular tension and aerodynamic effect. For phonation to occur, subglottal pressure must be sufficient to overcome both supraglottal air pressure and the glottal resistance or tension of the vocal folds. The actual process follows this rhythmic cycle:
1. Closing of the glottis.
2. Increasing of air pressure beneath the glottis.
3. Bursting apart of the fold from air pressure with release of a “puff” of compressed breath.
4. Reclosing of the folds under constant muscle tension, with temporarily decreased subglottal air pressure drawing or “sucking” the folds back together.
Air pressure beneath the glottis increases as air continues to flow from the lungs and trachea. Consequently, the cycle is repeated many times per second. The actual opening and closing of the folds is not a simple open and shut process. As previously noted, the vocal folds are actually muscular tissue shelves with vertical depth. Consequently, in each phonatory cycle, the folds open from bottom to top and from posterior to anterior. In closing, the inferior part of the folds closes before the superior part, and horizontal closure procceds from anterior to posterior. When seen using high-speed photography, the the motion of the folds actually appears wavelike. Each complete opening and closing of the glottis constitutes one cycle.
The rate of releaseof these pufft of air determines the fundamental frequency, or Fo of a speaker’s voice. Fundamental frequency varies, affected by age, gender, and voluntary control. For men,the average fundamental frequency of vocal folds vibration is 125 hertz (Hz, or cycle per second). The average fundamental frequency for women is faster, about 220 Hz. Not surprisingly, the fundamental frequency of infant’s and children’s voices is even faster. A faster Fo is heard as a higher pitch, whereas a slower Fo characterizes lower pitch.
Interaction of the lungs and the larynx is required for changes in fundamental frequency. Size and mass of the vocal folds determine the range of frequencies possible for a given speaker. You can change Fo through a combination of alteration of (1) vocal fold tension and (2) subglottal air pressure. Higher or rising Fo is associated with greater vocal fold tension and higher subglottal air pressure. A drop in Fo conversely,is associated with a reduction in vocal fold tension and, especially, lower subglottal pressure. When you are conversing (rapid connected speech), you fundamental frequency will vary constantly according to these two factors of vocal fold tension and subglottal air pressure. That variation is perceived as changes in intonation of your voice. More than fundamental frequency is produced by the rapid opening and closing of the glottis. As we noted, the movement of the folds is complex, and the folds actually open more slowly than they close. Consequently, a complex harmonic sound is produced by the opening and closing of the vocal folds. This secondary complex harmonic signal is composed of harmonics or overtones of the fundamental frequency. Thus, the sound that emerges is complex, more of a buzz. It is not recognizable as the human voice. Instead, it must pass through the resonatory system to develop those characteristics.
Intensity of voice, heard by listeners as loudness, results from an interaction of vocal fold characteristics and subglottal and supraglottal pressure. Greater loudness result from (1) increased subglottal pressure, (2) vocal fold control that allows rapid, firm, longer closure, and (3) expansion of the vocal tract for reduced supraglottal pressure. The opposite adjustments produce a more quiet voice intensity. Thus, a speaker whose voice is too soft can learn how to change respiration, phonation, and resonation to develop a louder voice.
In summary, vocal fold vibration is affected not only by the function of laryngeal structures but also by respiration (subglottal pressure) and resonation (supraglottal shaping and pressure). Feedback between and among these systems causes changes in their actions, resulting in the complex sound waveform that serves as the basis for speech.
RESONATION
Resonation occurs as the vibrating airstream passes through the pharyngeal, oral, and nasal cavities. These cavities can be altered in size, shape, and coupling, or connections. The resonating cavities selectively amplify parts of the complex sound produced by phonation. The result is what you perceive as the distinctive sound of an individual’s voice, also known as voice quality.
That quality of a person’s voice is produced primarily by a combination of the person’s habitual Fo range blended with the overtones that are amplified (made louder) or subdued by resonation. The influences of resonation on voice quality include.
1. The overall length of the vocal tract.
2. The relative length of the oral, nasal, and pharyngeal cavities.
3. Habitual muscle tensing (this can raise the larynx, which will change the size and shape of the pharynx.)
4. The size of the tongue in relation to the oral cavity.
5. The moistness and softness of the cavity walls (Greater moistness and softness is associated with a lower, more “hollow”-sounding voice.)
6. The relative opening of the jaw and lips during speaking (Wider openings correspond to amplification of higher frequencies.)
7. Relative openness of the velopharyngeal port during production of vowels and oral resonant consonants(Greater opening will give a ”nasal” quality to the voice.)
The low resonance pattern characteristic of the Dsney cartoon character Goofy voice exemplifies the interaction of these factors. The low, hollow-sounding voice of this character is produced by tongue posture low and back (greater cavity space), small openings (lips, between resonating cavities), and soft, moist cavity walls. These adjustment amplify lower harmonics and are associated with the character’s distinctive voice.
Overall, the process of resonation shapes and amplifies selected frequencies of the laryngeal tone. It does not occur in isolation but is affected by the nature of respiration, phonation, and articulation processes. It also plays a role in articulation , as you will see in the next section.
ARTICULATION
Articulation is defined as the shaping of the voiced or unvoiced breath stream to form the sounds of speech. The vowels and resonant consonants (/m/, /n/, /0/, /l/, /r/, /w/, and /j/.) are articulated primarily by adjustments in resonance. For example, the nasal consonants /m/, /n/, and /0/ are all articulated with the velopharyngeal port open, or coupled to the pharynx. For /m/, the lips are closed (bilabial) : for /n/, the tongue tip touches the alveolar ridge (lingua alveolar). The fairly fixed position of the oral articulations, combined with the open velopharyngeal port, produces the distinctive resonance characteristics of nasal consonants. For /l/ and /r/ production, the voiced airstream flows through relatively fixed oral articulators, and the velopharyngeal prt is closed. Additionally, the characteristic resonances of different vowels are produced by adjustments in the oral cavity.
In contrast, the remaining consonants are shaped by the action of the tongue, jaw, and lips. The velopharyngeal port is closed for articulation of these consonants. If airflow is constricted between maxillary incisors and lower lip, /f/ (unvoiced airstream0 or /v/ (voiced airstream) result. This friction-like quality is also characteristic of nonresonant consonants produced with constriction in other parts of the oral cavity, for example, the alveolar ridge(/s/) and palate(/0/). Another type of nonresonant consonant is produced when the outgoing airstream is suddenly stopped and (sometimes) released. Such closure with the lips produces the bilabial /p/ (unvoiced) and /b/ (voiced). Similarly, air s stopped between the tongue tip and the alveolar ridge for /t/ and /d/. detailed description of the articulatory process will be found in Chapters 3, 4, and 5.
Even this short discussion should make it clear that speech production is not a simple, one-step-at-a-time process, beginning with the lungs and ending with a stream of articulated speech sounds. The breath stream for speech, provided by the respiratory system, is constantly adjusting in response to the activity of the vocal folds, resonators, and articulators. Laryngeal changes in frequency of vibration characterize connected speech and also require reciprocal adjustments across systems. Precise timing between articulation and phonation is necessary to produce appropriate voicing for consonants. Upper airway pressure changes, resulting from movement of the articulators, require change in the glottis and the respiratory system. If each process operated independently of each other, fluent speech would be impossible. It is the simultaneous and cooperative functioning of these system and their structures that allows us to produce speech.
REVIEW VOCABULARY
Abducted/abduction: structures drawn apart from the midline(e.g., when the vocal folds are abducted, the glottis is open)
Adducted/adduction: structures drawn together toward the midline ( e.g., when the vocal folds are adducted, the glottis is closed)
Alveolar ridge: prominent ridge behind the maxillary incisors and the cuspid (canine) teeth.
Alveoli: located in the alveolar sacs (termination of alveolar ducts) in the lungs; site of actual exchange of oxygen and carbon dioxide.
Apex (tongue): anterior end of the tongue.
Approximated: degree of closeness of vocal folds.
Articulation: shaping of outgoing breath stream into the sound of speech.
Arytenoids cartilages: small, pyramidal-shaped cartilages that rest on top of the posterior cricoids cartilage; form movable, posterior attachments for vocal folds.
Bilabial: both lips.
Blade (singular bronchus): two primary divisions from the trachea that lead into the right and left lung.
Bronchioles: smaller branches of the bronchi.
Cricoid cartilage: ring-shaped base/most inferior cartilage of the larynx; arytenoids cartilages are positioned superiorly on its posterior expanded portion.
Dental: referring to the teeth; (inter) dental consonants are produced with the tongue tip against or between the teeth.
Diaphragm: primary muscle of inhalation; dome-shaped, separating the abdominal and thoracic cavities.
Dorsum (tongue): upper surface of tongue.
Egressive: outgoing; refers to airstream in exhalation.
Exhalation: expulsion of air from the lungs; provides outgoing airstream for speech; half of a respiratory cycle.
Fundamental frequency: in reference to voice, rate at which the glottis opens and closes; measured in Hz. During phonation; heard by listener as pitch of voice.
Glottis: space between the vocal folds; may be open or closed; adjective, glottal.
Harmonic: a sound that is harmonic has a systematic pattern of vibration that is repeated at regular time intervals.
Phonation : vocal fold vibration, produced in the larynx.
Pitch : the property of a sound that is determined by the frequency of vibration.
Resonation : process of modifying a sound by passing it through a cavity of air.
Rib cage : bony framework encasing the lungs; movement involved in respiration.
Soft palate : see velum
Subglottal structures : portions of the speech tract lying inferior to the laryngeal structures; consist of lungs, bronchi, bronchioles, alveoli, and trachea.
Also known as the respiratory system.
Supraglottal structures : structures lying superior to the glottis (e.g.,epiglottis and tongue)
Thoracic : related to the thorax
Thorax : body cavity containing heart and lungs bounded by spinal column, ribcage, sternum, and diaphragm.
Thyroid cartilage : largest cartilages in the larynx, its halves are closed anteriorly and open posteriorly ; anterior attachment point for vocal folds.
Tongue tip: most anterior point of tongue ; used for articulation of many consonant.
Trachea: windpipe, composed of cartilaginous rings, connecting the larynx with the bronchi and lungs.
Velopharyngeal port : opening that connects the nasopharynx and the oropharynx.
Velum : the soft muscular posterior third of the roof of the mouth, attached to the hard palate; can be raised or lowered; adjective, velar.
Vocal fold : muscular shelves in the larynx, extending from the thyroid cartilage (anteriorly) to the arytenoids cartilages (posteriorly)
Voice quality: the distinctive sound resulting from a combination of habitual range of fundamental frequency, blended with overtones amplified or subdued through resonation.
Voiced/voiceless: refers to the presence/absence of vocal fold vibration. Voiced sound are produced with vocal fold vibration; voiceless sounds are produced without vocal fold vibration.
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