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Speech

SPEECH

Speech consists of the sounds that humans produce, most often for the purpose of expressing language orally. Speech is just one mode of expressive language; other modes are writing and the production of manual signs. Very generally, language is a system of symbols that humans use to communicate. (See Language Disorders entry in this volume.)

Although most of the time speech sounds are produced in various combinations that convey meaning (and thus are being used to express language), their combinations can be meaningless (e.g., bababa). The meaningfulness aspect is the purview of language. The physical production aspect is the purview of speech.

The production of speech sounds requires that head, neck, and trunk muscles work in a coordinated fashion. Speech is often described in terms of the following component processes: respiration, phonation (voicing), resonance, and articulation. The respiratory system is the power source for our ability to produce sound. In the context of speech production, the air in our lungs is exhaled via active and passive thoracic and abdominal muscle activity, until it is halted at the larynx (in the case of voiced sounds).

The larynx sits at the top of the trachea and is comprised of muscle, cartilage, and membrane. In the context of speech production, the larynx is involved in voicing. Most speech sounds are voiced, but some are not (e.g., /s/). Without voicing, speech would be whispered. Airflow from the lungs is halted by the vocal folds (cords) of the larynx because they are closely approximated at midline. Eventually, air pressure builds up below the folds and forces them apart. The air flowing through the vocal folds sets into motion their vibration and also their cyclic opening and closing. Muscles are not the only laryngeal structures involved in voicing; the arytenoid cartilages also play an important role (their rocking motion toward midline helps to achieve complete closure of the vocal folds). The voice can change in pitch and loudness, and these too are functions of the larynx.

The vast majority of speech sounds are nonnasal (e.g., /b/, /d/), but a few are nasal (e.g., /m/, /n/). During the production of nasal sounds, the airflow above the vocal folds passes through the nasal and oral cavities. The airflow passes through the oral cavity alone during the production of nonnasal sounds. Thus, speech sounds have either a nasal or an oral resonance. Nonnasal sounds are produced when the soft palate (a muscle) moves upward and backward to make contact with the pharyngeal walls to block air from escaping through the nasal port. The soft palate is relaxed and the nasal port is open during the production of nasal sounds.

The speech sound is altered further by changing the position of the following structures of the oral cavity in relation to one another: lips, tongue, teeth, and jaw. These structures are known as the articulators, and their movement is known as articulation. In the articulation of some speech sounds, the flow of air is constricted but not stopped (e.g., /f/, /z/), whereas other speech sounds are produced by stopping the air in the oral cavity (e.g., /b/, /k/).

The central nervous system (e.g., motor cortex, upper motor neurons (UMNs), basal ganglia, cerebellum) and the peripheral nervous system (e.g., cranial and spinal nerves) are involved in speech production. UMNs originate in the primary motor cortex and project to cells in the brainstem or spinal cord. Lower motor neurons (LMNs) begin in the brainstem (cranial nerves) or spinal cord (spinal nerves) and project to the muscles on the same side of the body. For the most part, cranial nerves (which innervate head and neck muscles) receive input from left and right UMNs; this bilateral innervation offers superb protection. In the event of unilateral cortical/UMN damage, speech is affected minimally. However, unilateral cranial nerve damage has more devastating consequences for speech.

Older and younger adults can guess fairly accurately the chronological age of elderly individuals by listening to them speak (Caruso, Mueller, and Xue). However, physiological age rather than chronological age may be a better predictor of who is perceived as having an aging voice (Ramig and Ringel). Respiration and phonation are most affected by the aging process. Older people may have a restricted loudness range due to reduced vital capacity. The voice of older individuals is often perceived as hoarse. The physiological correlate of hoarseness is aperiodicity of vocal fold movement, which in the older adult may be caused by physical changes in the vocal folds (e.g., atrophy, bowing) or dehydration of the vocal folds because of decreased laryngeal gland secretions. The older voice is sometimes perceived as breathy and reduced in loudness, either of which may be due to reduced vital capacity and/or incomplete valving at the level of the larynx because of tissue changes in the vocal folds (atrophy, bowing) and/or because of changes to the laryngeal cartilages (ossification and calcification). There is not much change in the pitch of the female voice with age, except with extreme old age (higher pitch). As males age, pitch rises. A higher pitch may be the result of thinning vocal folds.

Several disease processes associated with aging can negatively affect speech production. Stroke and Parkinsons disease (PD) can result in dysarthria, a motor speech disorder characterized by weakness, slowness, reduced range of motion, or dyscoordination of any or all of the muscles of speech. Poststroke speech impairments can include imprecise consonant articulation, a breathy voice, strained-strangled phonation, and/or hypernasality. The underlying pathophysiology of the dysarthria associated with PD is muscle rigidity, with resulting speech characteristics of monopitch, monoloudness, and reduced stress. Another motor speech disorder is apraxia of speech (AOS), a deficit in the ability to program or plan the motor movements of speech. Stroke is the most common cause of AOS.

Speech-language pathologists diagnose and treat motor speech disorders in older adults. Contact the American Speech-Language-Hearing Association for more information about speech disorders (www.asha.org).

Susan Jackson

See also Brain; Hearing; Language Disorders; Parinsonism; Stroke.

BIBLIOGRAPHY

Caruso, A. J.; Mueller, P. B.; and Xue, A. The Relative Contributions of Voice and Articulation to Listener Judgements of Age and Gender: Preliminary Data and Implications. Voice 3 (1994): 311.

Duffy, J. R. Motor Speech Disorders. St. Louis: Mosby, 1995.

Ramig, L. O., and Ringel, R. L. Effects of Physiological Aging on Selected Acoustic Characteristics of Voice. Journal of Speech and Hearing Research 26 (1983): 2230.

Yorkston, K. M.; Beukelman, D. R.; Strand, E. A.; and Bell, K. R. Management of Motor Speech Disorders in Children and Adults, 2d ed. Austin: PRO-ED, 1999.

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Speech

Speech

Speech is defined as the ability to communicate thoughts, ideas, or other information by means of sounds that have clear meaning to others.

Many animals make sounds that might seem to be a form of speech. For example, one may sound an alarm that a predator is in the area. The sound warns others of the same species that an enemy is in their territory. Or an animal may make soothing sounds to let offspring know that a parent is present. Most scientists regard these sounds as something other than true speech.

Some animals can copy human speech to a certain extent also. Many birds, for example, can repeat words that they have been taught. This form of mimicry also does not qualify as true speech.

True speech consists of two essential elements. First, an organism has to be able to develop and phrase thoughts to be expressed. Second, the organism has to have the anatomical equipment with which to utter clear words that convey those thoughts. Most scientists believe that humans are the only species capable of speech.

Speech has been a critical element in the evolution of the human species. It is a means by which a people's history can be handed down from one generation to the next. It enables one person to convey knowledge to a roomful of other people. It can be used to amuse, to rouse, to anger, to express sadness, to communicate needs that arise between two or more humans.

The anatomy of speech

Spoken words are produced when air expelled from the lungs passes through a series of structures within the chest and throat and passes out through the mouth. The structures involved in that process are as follows: air that leaves the lungs travels up the trachea (windpipe) into the larynx. (The larynx is a longish tube that joins the trachea to the lower part of the mouth.) Two sections of the larynx consist of two thick, muscular folds of tissue known as the vocal cords. When a person is simply breathing, the vocal cords are relaxed. Air passes through them easily without producing a sound.

When a person wishes to say a word, muscles in the vocal cords tighten up. Air that passes through the tightened vocal cords begins to vibrate, producing a sound. The nature of that sound depends on factors such as how much air is pushed through the vocal cords and how tightly the vocal cords are stretched.

Words to Know

Anatomical structure: A part of the body.

Aphasia: The inability to express or understand speech or the written word.

Broca's area: The part of the brain that controls the anatomical structures that make speech possible.

Epiglottis: The flap at the top of the larynx that regulates air movement and prevents food from entering the trachea.

Larynx: A tube that joins the trachea to the lower part of the mouth.

Palate: The roof of the mouth.

Trachea: The windpipe; a tube that joins the larynx to the lungs.

Vocal cords: Muscular folds of tissue located in the larynx involved in the production of sounds.

The moving airnow a form of soundpasses upward and out of the larynx. A flap at the top of the larynx, the epiglottis, opens and closes to allow air to enter and leave the larynx. The epiglottis is closed when a person is eatingpreventing food from passing into the larynx and tracheabut is open when a person breathes or speaks.

Once a sound leaves the vocal cords, it is altered by other structures in the mouth, such as the tongue and lips. A person can form these structures into various shapes to make different sounds. Saying the letters "d," "m," and "p" exemplifies how your lips and tongues are involved in this process.

Other parts of the mouth also contribute to the sound that is finally produced. These parts include the soft palate (roof) at the back of the mouth, the hard or bony palate in the front, and the teeth. The nose also provides an alternate means of issuing sound and is part of the production of speech. Movement of the entire lower jaw can alter the size of the mouth cavern and influence the tone and volume of the speech.

The tongue is the most agile body part in forming sounds. It is a powerful muscle that can take many shapesflat, convex, curledand can move front and back to contact the palate, teeth, or gums. The front of the tongue may move upward to contact the hard palate while the back of the tongue is depressed. Essentially these movements open or obstruct the passage of air through the mouth. During speech, the tongue moves rapidly and changes shapes constantly to form partial or complete closure of the vocal tract necessary to manufacture words.

The brain

Other animals have anatomical structures similar to those described above. Yet, they do not speak. The reason that they lack speech is that they lack the brain development needed to form ideas that can be expressed in words.

In humans, the part of the brain that controls the anatomical structures that make speech possible is known as Broca's area. It is located in the left hemisphere (half) of the brain for right-handed and most left-handed people. Nerves from Broca's area lead to the neck and face and control movements of the tongue, lips, and jaws.

The portion of the brain in which language is recognized is situated in the right hemisphere. This separation leads to an interesting phenomenon: a person who loses the capacity for speech still may be able to understand what is spoken to him or her and vice versa. The loss of the power of speech or the ability to understand speech or the written word is called aphasia.

Three speech disorders result from damage to the speech center, dysarthria, dysphonia, and aphasia. Dysarthria is an inability to speak clearly because of weakness in the muscles that form words. Dysphonia is a hoarseness of the voice that can be caused by a brain tumor or any number of other factors. And aphasia can be either the inability to express thoughts in speech or writing or the inability to read or to understand speech.

[See also Brain ]

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SPEECH

SPEECH
1. The primary form of LANGUAGE; oral COMMUNICATION in general and on any particular occasion: Most people are more fluent in speech than in writing.

2. A usually formal occasion when a person addresses an audience, often with the help of notes or a prepared text.

3. A way of speaking, often involving a judgement of some kind: local speech, slovenly speech, standard speech.

4. The field of study associated with speaking and listening: the science of speech.

Anatomy and physiology

Speech is possible because of the development over millennia of an appropriate physical system: the diaphragm, lungs, throat, mouth, and nose, working together. All such organs preexisted the evolution of language and have such prior purposes as breathing, eating, and drinking. With the advent of speech, they continued to perform these functions while becoming available for additional uses, so that two systems (maintenance of the body and systematic communication) exist side by side. Vocal sound becomes possible when a stream of air is breathed out from the lungs and passes through the larynx, then into and through the pharynx, mouth, and nose. This sound may be voiced or voiceless: that is, the larynx may vibrate or not. Different sounds are made in the mouth by moving the lips, tongue, and lower jaw to change the size and shape of the channel through which the air passes. A CONSONANT is made with a narrowing of the channel, and the point of maximum narrowing is the place (or point) of articulation for that consonant. The way in which this is done is the manner of articulation. A VOWEL typically has a wider channel than a consonant. Since it is difficult to be precise about the articulation of vowels, they are normally described by their auditory quality. In discussing articulation, phoneticians refer to an articulator, which may be active (as with the lips and tongue) or passive (as with the front teeth).

Place of articulation

For bilabial consonants, the narrowing is achieved by bringing the lips together. For labio-dental consonants, the active articulator is the lower lip. In other cases, the active articulator is part of the tongue, which is raised towards the passive articulator on the roof of the mouth: see table.

Sounds can be classified according to the active articulator, for example the tongue: apical sounds made with the tip (Latin apex); laminal sounds with the blade (Latin lamina); dorsal sounds with the back (Latin dorsum). Retroflex sounds are made with the tip of the tongue curled back behind the alveolar ridge towards the PALATE. However, the commonest classification is according to the passive articulator. This terminology assumes that the active articulator is the organ that lies opposite the passive articulator in the state of rest: for example, the passive articulator of a dental sound is the upper front teeth, and the active articulator is the tip of the tongue. If some other active articulator is used, it is specified explicitly: for example for /f, v/, the lower lip moves up to the upper teeth, and these sounds are labio-dental: see table. The ASPIRATE /h/ is usually described as glottal. In English, /h/ is like a voiceless vowel in that there is no fricative-like narrowing in the mouth, so that the greatest point of narrowing is in the glottis. Most sounds have one place of articulation, but /w/ has a double articulation, being made by simultaneously rounding the lips and raising the back of the tongue towards the VELUM. It is thus both bilabial and velar.

Manner of articulation

This refers mainly to the degree of narrowing at the place of articulation of a sound. If the airstream is blocked completely, the result is a STOP, such as /b/, but if it is narrowed to the point where noise or turbulence is generated as air passes through the gap, the resulting sound is a FRICATIVE /v/. In the case of an APPROXIMANT or continuant, the manner of articulation is more open, as with the /r/ of rink as compared to the /z/ of zinc (a voiced fricative). When a stop is released, the articulators move apart and necessarily pass through the degree of narrowing which produces fricative noise. A PLOSIVE is released quickly, whereas an AFFRICATE is released slowly:

plosives

/p, b; t, d; k, g/

affricates

/tʃ, dʒ/

fricatives

/f, v; θ, ð; s, z; ʃ, ʒ; h/



There are several types of approximant. The velum is normally raised to prevent air from entering the nose: a NASAL is produced with the velum lowered. The airstream normally passes centrally through the mouth: in the case of a lateral, the air escapes at the sides. The tongue normally offers a convex surface to the roof of the mouth: for an r-sound, the tongue surface is often hollowed out and the tip raised. A GLIDE or semi-vowel is vowel-like and moves rapidly into the following vowel, and cannot be prolonged:

nasals

/m, n, ŋ/

lateral

/l/

r-sound

/r/

glides

/j, w/

Phoneticians conventionally describe consonants according to their articulation.

Articulator

Description

Examples

Active

Passive

lower and upper lips

labial

/p, b, m/

lower lip

front teeth

labio-dental

/f, v/

tongue:



tip

front teeth

dental

/θ, ð/

 tip

alveolar ridge

alveolar

/t, d, s, z, n, l, r/

 tip/blade

ridge/palate

palato-alveolar

/ʃ, ʒ, tʃ, dʒ/

 front

palate

palatal

/j/

 back

velum

velar

/k, g, ŋ/


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Speech

382. Speech

See also 236. LANGUAGE ; 330. PRONUNCIATION ; 354. RHETORIC and RHETORICAL DEVICES ; 380. SOUND .

acyrology
1. an incorrectness in diction.
2. cacology. acyrological, adj.
alogy, alogia
Medicine. an inability to speak, especially as the result of a brain lesion.
aphasia
Pathology. an impairment or loss of the faculty of understanding or using spoken or written language. aphasiac, n. aphasic, n., adj.
aphonia, aphony
loss of the power of speech; dumbness. aphonic, apho-nous, adj.
aphrasia
loss or absence of the power of speech.
biloquism
the ability to speak in two distinct voices. biloquist, n.
cacology
1. a defectively produced speech.
2. socially unacceptable enunciation.
3. nonconformist pronunciation.
deafmutism
the condition of lacking both hearing and speech. Also called surdomutism. deafmute, n.
dyslogy, dyslogia
Pathology. an inability to express ideas or reasoning in speech because of a mental disorder.
dysphasia
an impaired state of the power of speech or of the ability to comprehend language, caused by injury to the brain.
dysphemia
any neurotic disorder of speech; stammering.
dysphonia
speech problems resulting from damage to or malformation of the speech organs.
echolalia
the uncontrollable and immediate repetition of sounds and words heard from others. echolalic, adj.
elocution
1. the art of public speaking.
2. the manner or quality of a persons speech. elocutionist, n.
galimatias
confused or unintelligible speech; gibberish.
glossograph
an instrument for recording the movements of the tongue during speech.
glossolalia
an ecstatic, usually unintelligible speech uttered in the worship services of any of several sects stressing emotionality and religious fervor. Also called speaking in tongues. glossolalist, n.
glossophobia
an abnormal fear of speaking in public or of trying to speak.
gutturalism
a throaty manner of speaking.
hyperphasia
a condition in which control of the speech organs is lost, resulting in meaningless and deranged speech.
labialism
a tendency to articulate sounds with the lips rounded.
lalomania
an abnormal love of speech or talking.
lalopathology
the branch of medical science that studies disorders of speech. lalopathy, n. lalopathic, adj.
lalophobia
an abnormal fear of speaking.
logopedia, logopaedia
Pathology. the science that studies speech defects and their treatment. Also logopedics, logopaedics. logopedie, logopaedic, adj.
mogilalia
a pathological speech problem, as stammering.
mutism
Psychiatry. a conscious or unconscious refusal to make verbal responses to questions, present in some mental disorders.
neolalia
any speech that contains new words unintelligible to a hearer. See also 334. PSYCHOLOGY .
obmutescence
Obsolete, loss of speech or the act of keeping silence.
paralalia
a speech defect or disorder in which sounds are distorted.
paralogia
a disorder of the faculty of reasoning, characterized by discon-nected and meaningless speech.
paraphasia
aphasia characterized by the inability to find the correct words to express meaning.
paraphrasia
garbled or incoherent speech, the result of aphasia.
pectoriloquism, pectoriloquy
speaking from the chest, a phenomenon observed with a stethoscope and caused by the voice reverberating in the lung cavities as a result of disease. pectoriloquial, pectoriloquous, adj.
psellism
the condition of stuttering or stammering.
psittacism
a mechanical, repetitive, and usually meaningless speech.
surdomutism
deafmutism. surdomute, n.
susurration
1. the act or process of whispering.
2. a whispering sound or soft rustling. Also susurrus. susurrant, susurrous, adj.
tachyphrasia
an abnormality of speech characterized by extreme volubility.
tautophony
repetition of the same sound. tautophonic, tautophonical, adj.
traulism
a stammering and stuttering speech.
ventrilocution
ventriloquism.
ventriloquism
the art or practice of speaking so that the voice seems not to come from the speaker but from another source, as from a mechanical doll. Also called ventriloquy, ventrilocution, gastriloquism. ventriloquist, n. ven-triloquistic, adj.
verbigeration
meaningless repetition of words and phrases.

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speech

speech involves voluntary initiation and involvement of a complex set of muscles around the larynx, throat, and mouth, together with interruption of the rhythm of breathing and utilization of the muscles of expiration. Like other patterns of voluntary movement, speech originates in the cerebral cortex. Several other parts of the brain (notably the cerebellum), together with sensory feedback, modify and regulate the outgoing nerve impulses to the motor neurons whose axons activate the relevant muscles. In this instance, the motor neurons concerned are in the brain stem, and their axons travel in the lowermost cranial nerves to the muscles of the vocal apparatus. Effective speech depends also on the motor neurons in the cervical and thoracic parts of the spinal cord that serve the muscles of breathing.

The process of speech production, speech transmission, and speech perception is often referred to as the speech chain. It is the configuration of the human vocal tract that gives rise to the acoustic properties of speech. The major speech articulators are the lips, jaw, the body, tip and velum of the tongue, and the hyoid bone position (which sets larynx height and pharynx width). The configuration of the speech articulators and their co-ordinated movement generate the acoustic consequences that we perceive as the sounds of our language. These phonemes (the consonant and vowel units of language) are not produced in a sequential and isolated manner but rather are co-articulated, and they coalesce to form a complex sound stream. The speech production system may be thought of as a set of physical acoustic sources (e.g. larynx) and physiologically-determined filters (e.g. lips) that are combined. The human speech system is particularly well suited for the rapid transfer of information.

There are a variety of ways to produce speech sounds. One method involves using the air pressure provided by the lungs to cause the vocal folds of the larynx to vibrate. The resulting sound can be altered by a variety of constrictions or closures in parts of the upper vocal tract. The modern study of the physiology of speech production began in 1928 with Stetson, who measured the speed and force of articulators. The development of X-ray photography led to the dynamic visualization of the vocal tract during speech production. The sound spectrograph (developed by Koenig in the 1940s) made it possible to study speech acoustic events in greater detail and revealed phoneme-specific information in the acoustic patterns. In particular, vowel formants and consonant-dependent formant transitions were recognized as key components to phoneme identity, leading to the initial attempts at computer speech synthesis.

The acoustic properties vary among different speakers producing the same sound and, more crucially, each utterance produced by an individual is unique. The mapping between the variable acoustic characteristics of speech production and the successful and stable identification of linguistically meaningful units in speech production is a major paradox. Recent research suggests that visual information is used to resolve acoustic difficulties in speech perception.

Marjorie Lorch


See also jaw; language; larynx; lip-reading; tongue; voice.

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speech

speech / spēch/ • n. 1. the expression of or the ability to express thoughts and feelings by articulate sounds: he was born deaf and without the power of speech. ∎  a person's style of speaking: she wouldn't accept his correction of her speech. ∎  the language of a nation, region, or group: the distinctive rhythms of their speech. 2. a formal address or discourse delivered to an audience: the headmistress made a speech about how much they would miss her. ∎  a sequence of lines written for one character in a play.

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speech

speech act of speaking. OE. (Angl.) spēc, (WS.) spǣċ, rel. to specan SPEAK; repl. earlier sprǣċ = OS. sprāka (Du. spraak), OHG. sprāhha (G. sprache), WGmc. sb. f. *sprǣk- *sprek- SPEAK.
Hence speechify make a speech or speeches (usu. with derogatory force) XVIII.

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speech

speech: see language.

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speech

speechbeach, beech, beseech, bleach, breach, breech, each, impeach, leach, leech, outreach, peach, pleach, preach, reach, screech, speech, teach •horseleech

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Speech

Speech

Evolution of speech

The physiology of speech

The brain

Speech impediments

Speech is defined as the ability to convey thoughts, ideas, or other information by means of articulating sound into meaningful words.

Many animals can make sounds and some can tailor these sounds to a given occasion. They may sound an alarm that a predator is in the area, warning others of their species that something has trespassed into their territory. Animals may make soothing sounds to let offspring know that their parent is present. These are only sounds of varying pitch or volume and do not constitute speech. Some animals, notably birds, can copy human speech to a minor extent and repeat words that they have been taught. This may be speech but limited control of vocal cords and a lack of flexible lips restricts the sounds that birds can imitate.

Some great apes such as the gorilla have been taught speech via sign language. They do not have the ability to form words because their larynx is not constructed to allow them to form certain sounds necessary for human speech. Some researchers have worked diligently to teach an ape to sign with its hands, to point to symbols in a board, or arrange marked blocks to form a thought, however incomplete. Thus, a gorilla can indicate that he or she wants an orange, wants to rest, or is cold but cannot communicate outside of these limited signs. A gorilla certainly cannot speak. One chimpanzee learned to sign more than 100 words and to put two or three symbols together to ask for something, but she was never able to place symbols together to express an idea.

Speech is unique to the human species. It is a means by which a peoples history can be handed down from one generation to the next. It enables one person to convey knowledge to a roomful of other people. It can be used to amuse, to rouse, to anger, to express sadness, to communicate needs that arise between two or more humans.

Evolution of speech

How have humans evolved to have the ability to talk while our close cousins, the great apes, have not? No definite answer can be given to that question though theories have been put forth.

One widely accepted theory has to do with the humans assumption of an erect (standing) position and the change that this brought to the anatomy of the skull. Following the evolution of human skulls from their earliest ancestors, one major change that occured is the movement of the foramen magnum (the large hole in the skull through which the spinal cord passes) to connect with the base of the brain. In early skulls, the foramen magnum is at the back of the skull because early man walked bent over with his head held to look straight ahead. The spinal cord entered the skull from behind as it does in apes and other animals. In modern humans, the opening is on the bottom of the skull, reflecting humans erect walk and his or hers skull placement atop the spine.

As humans position changed and the manner in which his or her skull balanced on the spinal column pivoted, the brain expanded, altering the shape of the cranium. The most important change wrought by humans upright stance is the position of the larynx in relation to the back of the oral cavity. As man became erect, his larynx moved deeper into the throat and farther away from the soft palate at the back of the mouth. This opened a longer resonating cavity that is responsible for the low vocal tones that man is capable of sounding.

The expanded brain allowed the development of the speech center where words could be stored and recalled. A more sophisticated auditory center provided the means by which speech by others of the same species could be recognized. Over time, and with greater control of the articulating surfaces, consonant sounds were added to the vocabulary. Initial sounds by hominids probably were vowels, as evidenced by current ape communication.

The physiology of speech

Speech requires movement of sound waves through the air. Speech itself is air that is moved from the lungs through a series of anatomic structures that mold sound waves into intelligible speech. This capacity can be accomplished in any volume from a soft whisper to a loud shout by varying the force and volume of air expelled from the lungs. All languages are spoken by the same mechanism, though the words are different and require different usages of the anatomy.

To expel air from the lungs the diaphragm at the floor of the thorax is relaxed. This allows the diaphragm to return to its resting position which is domed into the thorax, expelling air from the lungs. Also, the muscles of the chest tighten, reducing the size of the interior thorax to push more air from the lungs. The air travels up the windpipe (trachea) and passes through the larynx.

The larynx is comprised of a number of cartilages. The largest is the cricoid cartilage which is joined to the top of the trachea. It is structurally different from the rings that form the trachea. The cricoid is a complete cartilaginous ring, while the tracheal rings are horse shoe shaped (open in the back). The back of the cricoid is a large, solid plate. The front slopes down sharply and forms a V angle. Atop the cricoid lies the thyroid cartilage, which is more elongated front to back in males. The cartilage forms an angle of about 90° in males. In females the cartilage is flatter, forming an angle of 120°. Thus the male cartilage protrudes farther forward and often is evident as a knob in front of the throat (known as the Adams apple).

The two cartilages form a hard cartilagineous box that initiates sound by means of the vocal cords that lie at the upper end of the box. The glottis, entrance to the larynx at the upper end, is protected by a flap called the epiglottis. The flap is open during the process of breathing but closes over the glottis when food is swallowed. Both air and food traverse the same area in the throat, the pharynx, and the epiglottis prevents food from entering the trachea and directs air into the lungs. Infection of the epiglottis can occur when a child has a sore throat. The resulting inflammation can progress rapidly, cause complications in respiration, and may be fatal if not treated promptly because the inflamed epiglottis can close off the laryngeal opening.

If an individual is simply breathing and not talking, the vocal cords lie relaxed and open to allow free passage of air. A series of muscles in and around the larynx pulls the vocal cords taut when speech is required. The degree of stress on the cords dictates the tone of voice. Singing requires especially fine control of the laryngeal mechanism. Word emphasis and emotional stress originate here. Air puffs moving through the larynx place the vocal cords or vocal folds in a state of complex vibration. Starting from a closed configuration the vocal folds open first at the bottom. The opening progresses upward toward the top of the fold. Before the opening reaches the top of the vocal cord the bottom has closed again. Thus the folds are open at the bottom and middle, open at the middle and closed on each end, open at the middle and top, and then only at the top. This sequence is repeated in fine detail during speech.

Once the sound leaves the vocal cords it is shaped into words by other structures called articulators. These are the movable structures such as the tongue and lips that can be configured to form a given sound.

Above the larynx lies the pharynx through which the sound moves on its way to the mouth. The mouth is the final mechanism by which sound is tailored into words. The soft palate at the back of the mouth, the hard or bony palate in the front, the teeth, the tongue, and the lips come into play during speech. The nose also provides an alternate means of issuing sound and is part of the production of speech. Movement of the entire lower jaw can alter the size of the mouth cavern and influence the tone and volume of the speech. Speech is a complex series of events that takes place with little or no conscious control from the speaker other than selection of the words to be spoken and the tone and volume at which to deliver them. The speech center in the brain coordinates movement of the anatomic structures to make the selected words become reality. Speaking in louder tones is accomplished by greater force on the air expelled from the lungs. Normal speech is accompanied by normal levels of respiration. Whispering involves a reduction in the air volume passing through the vocal cords.

The tongue is the most agile of these articulators. Its musculature allows it to assume a number of configurations flat, convex, curled, etc. and to move front and back to contact the palate, teeth, or gums. The front of the tongue may move upward to contact the hard palate while the back of the tongue is depressed. Essentially these movements open or obstruct the passage of air through the mouth. During speech, the tongue moves rapidly and changes shapes constantly to form partial or complete occlusions of the vocal tract necessary to manufacture words. The vocal tract is open for formation of the vowels, moderately open to produce the R or L sounds, tightly constricted to S or F, and completely occluded for P and G.

In addition to the formation of words, speech entails rhythm. This rhythm can be seen by the motions made by the speaker as he or she talks. He or she may chop his or her hand or move his or her head in time to the stresses of speech, marking its rhythm. Rhythm is essentially the grouping of words and sounds in a time period. Rhythm often is most emphatic in childrens taunts: Thom-as is a teach-ers pet. In more complex speech the rhythm is not as exact but listeners are disposed to placing a rhythmic pattern on what they hear even though the speaker may not stress any such rhythm.

The brain

The speech center lies in the parietal lobe of the left hemisphere of the brain for right-handed persons and most left-handed. The area of the brain responsible for motor control of the anatomic structures is called Brocas motor speech area. It is named for Pierre Paul Broca (1824-80) a French anatomist and surgeon who carried out extensive studies on the brain. The motor nerves leading to the neck and face control movements of the tongue, lips, and jaws.

The language recognition center usually is situated in the right hemisphere. Thus a person who loses the capacity for speech still may be able to understand what is spoken to him or her and vice versa. The loss of the power of speech or the ability to understand speech or the written word is called aphasia.

Three speech disorders-dysarthria, dysphonia, and aphasia-result from damage to the speech center. Dysarthria is a defect in the articulation and rhythm of speech because of weakness in the muscles that form words. Amyotrophic lateral sclerosis (Lou Gehrigs disease) and myasthenia gravis are two diseases with which such muscle weakness can be associated. Dysphonia is a hoarseness of the voice that can be caused by a brain tumor or any number of nonneurologic factors. Aphasia can be either motor aphasia, which is the inability to express thoughts in speech or writing, or sensory aphasia, the inability to read or to understand speech.

The ability to speak is inherent in the human species. An infant is born with the ability to learn language but not to speak. Language is passed from one generation to the next. Children learn basic language easily and at a young age. From that time they add to their vocabulary as they accrueeducation and experience. A child will learn a language with the regional inflections inherent in his parents and peers speech.

Speech impediments

Speech can be negatively influenced by abnormalities in the structures responsible for making words. Thickening of the vocal cords or tumor growth on the vocal cords can deepen the tone of speech. A cleft palate, a congenital anomaly, can be a serious impediment of speech. A cleft lip with the palate intact is a lesser problem, but may still interfere with the proper formation of words. Fortunately, surgical correction of either of these impediments is easily carried out.

Traumatic changes that cause loss of part of the tongue or interfere in the movement of the jaw also can result in speech changes. Extended speech therapy can help to make up for the loss in articulation.

A stroke can interfere with the function of the speech center or cause of motor control over the muscles used in speech because it destroys the part of the brain controlling nerves to those structures. Destruction of the speech center can render an individual unable to form meaningful sentences or words. Once destroyed, brain tissue is not regenerated. Loss of the speech center may

KEY TERMS

Articulation The touching of one movable structure (such as the tongue) to another surface (such as the teeth) to form words.

Epiglottis The flap at the top of the larynx that regulates air movement and prevents food from entering the trachea. The epiglottis closes to prepare an individual to lift a heavy weight or to grunt.

Motor control The nerves that control the movements of muscles.

Parietal lobe A lobe of the brain that lies near the parietal bone.

mean a life without the ability to talk. In this case, the patient may need to rely solely on the written word. Recognition of speech and language is centered in a part of brain apart from the speech center so a patient still could recognize what was said to him or her.

Larry Blaser

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Speech

Speech

Speech is defined as the ability to convey thoughts, ideas, or other information by means of articulating sound into meaningful words.

Many animals can make sounds and some can tailor these sounds to a given occasion. They may sound an alarm that a predator is in the area, warning others of their species that something has trespassed into their territory. Animals may make soothing sounds to let offspring know that their parent is present. These are only sounds of varying pitch or volume and do not constitute speech. Some animals, notably birds , can copy human speech to a minor extent and repeat words that they have been taught. This may be speech but limited control of vocal cords and a lack of flexible lips restricts the sounds that birds can imitate.

Some great apes such as the gorilla have been taught speech via sign language. They do not have the ability to form words because their larynx is not constructed to allow them to form certain sounds necessary for human speech. Some researchers have worked diligently to teach an ape to sign with its hands, to point to symbols in a board, or arrange marked blocks to form a thought, however incomplete. Thus, a gorilla can indicate that he or she wants an orange, wants to rest, or is cold but cannot communicate outside of these limited signs. A gorilla certainly cannot speak. One chimpanzee learned to sign more than 100 words and to put two or three symbols together to ask for something, but she was never able to place symbols together to express an idea.

Speech is unique to the human species. It is a means by which a people's history can be handed down from one generation to the next. It enables one person to convey knowledge to a roomful of other people. It can be used to amuse, to rouse, to anger, to express sadness, to communicate needs that arise between two or more humans.


Evolution of speech

How have humans evolved to have the ability to talk while our close cousins, the great apes, have not? No definite answer can be given to that question though theories have been put forth.

One widely accepted theory has to do with the human's assumption of an erect (standing) position and the change that this brought to the anatomy of the skull. Following the evolution of human skulls from their earliest ancestors, one major change that occured is the movement of the foramen magnum (the large hole in the skull through which the spinal cord passes) to connect with the base of the brain . In early skulls, the foramen magnum is at the back of the skull because early man walked bent over with his head held to look straight ahead. The spinal cord entered the skull from behind as it does in apes and other animals. In modern humans, the opening is on the bottom of the skull, reflecting humans' erect walk and his or her's skull placement atop the spine.

As human's position changed and the manner in which his or her skull balanced on the spinal column pivoted, the brain expanded, altering the shape of the cranium. The most important change wrought by humans' upright stance is the position of the larynx in relation to the back of the oral cavity. As man became erect his larynx moved deeper into the throat and farther away from the soft palate at the back of the mouth. This opened a longer resonating cavity that is responsible for the low vocal tones that man is capable of sounding.

The expanded brain allowed the development of the speech center where words could be stored and recalled. A more sophisticated auditory center provided the means by which speech by others of the same species could be recognized. Over time , and with greater control of the articulating surfaces, consonant sounds were added to the vocabulary. Initial sounds by hominids probably were vowels, as evidenced by current ape communication.


The physiology of speech

Speech requires movement of sound waves through the air. Speech itself is air that is moved from the lungs through a series of anatomic structures that mold sound waves into intelligible speech. This capacity can be accomplished in any volume from a soft whisper to a loud shout by varying the force and volume of air expelled from the lungs. All languages are spoken by the same mechanism, though the words are different and require different usages of the anatomy.

To expel air from the lungs the diaphragm at the floor of the thorax is relaxed. This allows the diaphragm to return to its resting position which is domed into the thorax, expelling air from the lungs. Also, the muscles of the chest tighten, reducing the size of the interior thorax to push more air from the lungs. The air travels up the windpipe (trachea) and passes through the larynx.

The larynx is comprised of a number of cartilages. The largest is the cricoid cartilage which is joined to the top of the trachea. It is structurally different from the rings that form the trachea. The cricoid is a complete cartilaginous ring, while the tracheal rings are horseshoe shaped (open in the back). The back of the cricoid is a large, solid plate. The front slopes down sharply and forms a V angle. Atop the cricoid lies the thyroid cartilage, which is more elongated front to back in males. The cartilage forms an angle of about 90° in males. In females the cartilage is flatter, forming an angle of 120°. Thus the male cartilage protrudes farther forward and often is evident as a knob in front of the throat (known as the Adam's apple).

The two cartilages form a hard cartilagineous box that initiates sound by means of the vocal cords that lie at the upper end of the box. The glottis, entrance to the larynx at the upper end, is protected by a flap called the epiglottis. The flap is open during the process of breathing but closes over the glottis when food is swallowed. Both air and food traverse the same area in the throat, the pharynx, and the epiglottis prevents food from entering the trachea and directs air into the lungs. Infection of the epiglottis can occur when a child has a sore throat. The resulting inflammation can progress rapidly, cause complications in respiration , and may be fatal if not treated promptly because the inflamed epiglottis can close off the laryngeal opening.

If an individual is simply breathing and not talking, the vocal cords lie relaxed and open to allow free passage of air. A series of muscles in and around the larynx pulls the vocal cords taut when speech is required. The degree of stress on the cords dictates the tone of voice. Singing requires especially fine control of the laryngeal mechanism. Word emphasis and emotional stress originate here. Air puffs moving through the larynx place the vocal cords or vocal folds in a state of complex vibration. Starting from a closed configuration the vocal folds open first at the bottom. The opening progresses upward toward the top of the fold. Before the opening reaches the top of the vocal cord the bottom has closed again. Thus the folds are open at the bottom and middle, open at the middle and closed on each end, open at the middle and top, and then only at the top. This sequence is repeated in fine detail during speech.

Once the sound leaves the vocal cords it is shaped into words by other structures called articulators. These are the movable structures such as the tongue and lips that can be configured to form a given sound.

Above the larynx lies the pharynx through which the sound moves on its way to the mouth. The mouth is the final mechanism by which sound is tailored into words. The soft palate at the back of the mouth, the hard or bony palate in the front, the teeth, the tongue, and the lips come into play during speech. The nose also provides an alternate means of issuing sound and is part of the production of speech. Movement of the entire lower jaw can alter the size of the mouth cavern and influence the tone and volume of the speech. Speech is a complex series of events that takes place with little or no conscious control from the speaker other than selection of the words to be spoken and the tone and volume at which to deliver them. The speech center in the brain coordinates movement of the anatomic structures to make the selected words become reality. Speaking in louder tones is accomplished by greater force on the air expelled from the lungs. Normal speech is accompanied by normal levels of respiration. Whispering involves a reduction in the air volume passing through the vocal cords.

The tongue is the most agile of these articulators. Its musculature allows it to assume a number of configurations—flat, convex, curled, etc.—and to move front and back to contact the palate, teeth, or gums. The front of the tongue may move upward to contact the hard palate while the back of the tongue is depressed. Essentially these movements open or obstruct the passage of air through the mouth. During speech, the tongue moves rapidly and changes shapes constantly to form partial or complete occlusions of the vocal tract necessary to manufacture words. The vocal tract is open for formation of the vowels, moderately open to produce the R or L sounds, tightly constricted to S or F, and completely occluded for P and G.

In addition to the formation of words, speech entails rhythm. This rhythm can be seen by the motions made by the speaker as he or she talks. He or she may chop his or her hand or move his or her head in time to the stresses of speech, marking its rhythm. Rhythm is essentially the grouping of words and sounds in a time period. Rhythm often is most emphatic in children's taunts: "Thom-as is a teach-er's pet." In more complex speech the rhythm is not as exact but listeners are disposed to placing a rhythmic pattern on what they hear even though the speaker may not stress any such rhythm.


The brain

The speech center lies in the parietal lobe of the left hemisphere of the brain for right-handed persons and most left-handed. The area of the brain responsible for motor control of the anatomic structures is called Broca's motor speech area. It is named for Pierre Paul Broca (1824-80) a French anatomist and surgeon who carried out extensive studies on the brain. The motor nerves leading to the neck and face control movements of the tongue, lips, and jaws.

The language recognition center usually is situated in the right hemisphere. Thus a person who loses the capacity for speech still may be able to understand what is spoken to him or her and vice versa. The loss of the power of speech or the ability to understand speech or the written word is called aphasia .

Three speech disorders-dysarthria, dysphonia, and aphasia-result from damage to the speech center. Dysarthria is a defect in the articulation and rhythm of speech because of weakness in the muscles that form words. Amyotrophic lateral sclerosis (Lou Gehrig's disease ) and myasthenia gravis are two diseases with which such muscle weakness can be associated. Dysphonia is a hoarseness of the voice that can be caused by a brain tumor or any number of nonneurologic factors. Aphasia can be either motor aphasia, which is the inability to express thoughts in speech or writing, or sensory aphasia, the inability to read or to understand speech.

The ability to speak is inherent in the human species. An infant is born with the ability to learn language but not to speak. Language is passed from one generation to the next. Children learn basic language easily and at a young age. From that time they add to their vocabulary as they accrue education and experience. A child will learn a language with the regional inflections inherent in his parents' and peers' speech.


Speech impediments

Speech can be negatively influenced by abnormalities in the structures responsible for making words. Thickening of the vocal cords or tumor growth on the vocal cords can deepen the tone of speech. A cleft palate, a congenital anomaly, can be a serious impediment of speech. A cleft lip with the palate intact is a lesser problem, but may still interfere with the proper formation of words. Fortunately, surgical correction of either of these impediments is easily carried out.

Traumatic changes that cause loss of part of the tongue or interfere in the movement of the jaw also can result in speech changes. Extended speech therapy can help to make up for the loss in articulation.

A stroke can interfere with the function of the speech center or cause of motor control over the muscles used in speech because it destroys the part of the brain controlling nerves to those structures. Destruction of the speech center can render an individual unable to form meaningful sentences or words. Once destroyed, brain tissue is not regenerated. Loss of the speech center may mean a life without the ability to talk. In this case, the patient may need to rely solely on the written word. Recognition of speech and language is centered in a part of brain apart from the speech center so a patient still could recognize what was said to him or her.


Resources

periodicals

Roiphe, A.R. "Talking Trouble." Working Woman 19 (October 1994): 28-31.


Larry Blaser

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Articulation

—The touching of one movable structure (such as the tongue) to another surface (such as the teeth) to form words.

Epiglottis

—The flap at the top of the larynx that regulates air movement and prevents food from entering the trachea. The epiglottis closes to prepare an individual to lift a heavy weight or to grunt.

Motor control

—The nerves that control the movements of muscles.

Parietal lobe

—A lobe of the brain that lies near the parietal bone.

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