30 CHAPTER 1 INTRODUCTION AND ORIENTATION

constitute the locomotor system. The nervous and sen-sory systems form the neurosensory system, and thenervous and endocrine systems constitute the neuroen-docrine system. There are also systems within systems.The limbic system as part of the nervous system is butone example. Since the early 1980's, the immune or au-toimmune system has received a great deal of attention.

CLINICAL NOTE: The immune system functionslike a well-orchestrated team, with each successiveteam member further weakening an incoming mi-crobe. Initially, protein molecules called antibodiesimmobilize the invading microbe, which then enablesa large macrophage to engulf the invader. Themacrophage then "signals" white blood cells known asT cells that the immune system has been invaded. TheT cells, so named because they mature in the thymusgland, finish off the infected cell either by killing thecell directly or by stimulating B cells (another type ofwhite blood cell) to produce antibodies to kill the cell.The process is known as antibody-related immunity.The body contains as many as 100 million differentkinds ofantibodies and an equal variety of memory Tcells and memory B cells. The memory cells providelong-term protection against a subsequent invasion bythe same bacteria or virus.

Another type of immunity called cell-mediatedimmunity is particularly important in helping the bodycombat fungi, parasites, viruses, and tuberculosis. Cell-mediated immunity causesT cells to attack directlywithout the help of antibodies. A dramatic example ofwhat can occur when the immune system fails is the au-toimmune deficiency syndrome (AIDS). The humanimmunodeficiency viruses HIV-l and HIV-2-inparticular HIV-l-are responsible for AIDS. Anyonewho comes into physical contact with other humansshould be aware that blood and body fluids containingvisible blood are vehicles of the HIV virus. This alsoapplies to semen and vaginal secretions. Blood and bodyfluids containing visible blood from all clients should al-ways be handled as though they were infectious.l'

With just a moment of thought it becomes appar-ent that no one of these systems is independent of theothers. The speech mechanism draws heavily on somesystems and less heavily on others, but either directly orindirectly it is dependent upon all the systems in thebody. We shall be directing our attention to a goodshare of the skeletal, muscular; nenJOUS,and respiratory sys-tems. Sometimes our approach will be 1'egional andsometimes it will be systemic and, at times, a little of

9Hodine numbers: Center for Disease Control (CDC): 1-800-342-AIDS; Public Health Service Hotline: J-800-447-AIDS.

each, We shall be less concerned with the circulatoryand endocrine systems, and probably will mention thereproductive and digestive systems only in passing.

SPEECH PRODUCTION

The Need for anIntegrative ApproachEach of us, in our own minds, must generate a workingconstruct of me speech and hearing mechanisms. Con-structs are me personal property of the individuals re-sponsible for generating them, and a valuable componentin the battery of clinical and teaching tools we use in ourprofessional lives.We must realize mat constructs shouldnever become stereotyped and inflexible. They should beconstantly in a state of flux and subject to modification.Stereotyped constructs lead to stereotyped and inflexible clinicalmanagement.

In the pages that follow, we will become familiarwith the structures comprising the speech and hearingmechanisms. We will also be faced with the responsibil-ity of integrating these structures into a manageableworking construct.

Speech production is sometimes described as con-sisting of four phases: respiration, phonation, articu-lation, and resonance. This compartmentalization ofthe speech act is very unfortunate. It is incomplete, forone thing, because it completely neglects the role of thehearing mechanism and other avenues of feedback.l"

This compartmentalization also tends to conveythe impression of an unrealistic, temporal sequence ofevents leading to the production of speech. That is,first we breathe, then we phonate, then we articulate,finally the process of resonance takes place, and 10 andbehold! Out comes speech! It's like putting beads on astring.

A model of speech production is shown in Figure1-34. It illustrates the need for an integrative approachin generating a construct of speech production. Here,speech begins at the cortical level. The thought or re-sponse process leads to a sequence of neural impulsesthat are transmitted to the musculature of the breath-ing mechanism, to the larynx, and to the articulators.These neural impulses can be (but are not necessarily)delivered to all the musculature simultaneously, or toindividual structures. This model recognizes both tem-poral overlap and the mutual influence the structures

IOIt is interesting to see how quickly speech deteriorates when aperson cannot monitor me speech signal being produced, Smallwonder that me speech of the deaf and severely hearing handi-capped requires such long-term and patiently managed therapy.

SPEECH PRODUCTION 31

Auditory feedback

Conscious feedback from ~----- .... -------Cortical level Conscious feedback from- - - - - - .,_ - - - - - -. thought processes :..-------------

I muscles and tendonslead to

muscles and tendons II II tt II II II Sequential II Unconscious feedback from neural Unconscious feedback from IL ______ ...._____

commands to f4 - - - -_ - - - - - - - II muscles and tendons muscles of muscles and tendons II respiration, phonation II articulation tt Neural commands , Neural commands II II I II Temporal overlap t Temporal overlap II I I II

I I I I II

I I

Respiration Phonation Articulation

1• • t It t

Mutual influence Mutual influence

+ +

h

A model of speech production,

FIGURE 1-34

of the speech mechanism may have over one another.For example, we phonate and at the same time the artic-ulators are actively producing a meaningful sequence ofspeech sounds. In addition, changes in air flow resis-tance that occur during phonation and articulationinfluence the respiratory system, and the articulatoryprocess will, in many instances, influence the phona-tory mechanism.

Specialized receptors in our joints, tendons, andmuscles provide the brain with information about howwell things are going. Some of this information neverreaches the conscious level. Without feedback, audi-tory and proprioceptive, speech production wouldbe as haphazard as throwing darts in the dark. Weshould also recognize that this highly integrated andincredibly complex chain of events can be interrupted(by disease, for example) at virtually any stage to inter-fere with the normal processes of speech productionand reception.

Sound ProductionThose parts of the body most closely associated withspeech production include the lungs, the trachea, thelarynx, the nasal cavities, and the oral cavity (mouth).

These structures, shown in Figure 1-35, form a versa-tile and intricate sound production system.

Two absolute requirements for the production ofsounds of any kind are a source of energy and a vibrat-ing element. The primary source of energy for speechproduction is air provided by the lower respiratory tract,in particular the lungs. They supply the sound vibrators(the vocal folds in the larynx) with power in me form ofa fairly smooth unmodulated flow of air. We should note,however, that the conversion of a flow of air into soundmay take place almost anywhere along the vocal tract,which is that portion of the speech mechanism lyingabove (and including) the vocal folds.

Usually we think of the vibrating folds as the pri-mary source of sound for speech production, but thereare others. By constricting the vocal tract somewherealong its length, the air stream may become turbulent toproduce fricative noise. In addition, this turbulencemay be generated with or without vibration of the vocalfolds. Sounds may also be generated by momentarilyblocking the flow of air through the vocal tract. A sud-den release of the pressurized air may produce a mildexplosion or a plosive sound. The vocal folds, the lips,the tongue, or the soft palate may act as valves to blockthe flow of air and to release it.

32 CHAPTER 1 INTRODUCTION AND ORIENTATION

~ Hard palate

"L--- Soft palate

Pharyngeal cavity

Trachea

Lung tissue

Diaphragm

FIGURE 1-35

Schematic of the speech mechanism,

The quality of many speech sounds may be greatlymodified by changes in the configuration and thus theacoustical properties of the vocal tract, These changesare brought about mainly by modifications in the shapeof the oral cavity.

A physical analog of the speech mechanism mightconsist of a power supply, vibrating elements, a system ofvalves, and a filte7'ing device. No matter how the speechmechanism is represented, one of the first considera-tions is a power supply. Chapter 2 deals with the powersupply, or the breathing mechanism.

It will be difficult initially to incorporate the breath-ing mechanism into our model. The breatbing mecb-anism is an air pump, capable of supplying a variableair stream to the larynx and to the articulatory mecba-nism, each of which constitutes a variable resistance tome flow of air. Until we add these sources of resistanceto our model, the breathing mechanism must standalone.

BIBLIOGRAPHY AND READING LISTAlopour-Haghighi, F, 1. Titze, and P Durham, "Twitch Responsein the Canine Vocalis Muscle," J. Sp. H17lg, Res" 30, 1987,290-294.ASHA, AIDSIHIV Implications [or Speecb-Lrmgllage Pathologists andAudiologists, December, 1990.Basmajian, J. V, P1"i11l{/1YAl1at011lY, 7th ed. Baltimore: Williamsand Wilkins, 1976,Bloom, W, and D, Fawcett, A Textbook of Histology, 9m ed.Philadelphia: W. B, Saunders, 1968,

Cunningham, D, J, Textbook of Al1at01l1Y, 9th ed. New York: Ox-ford University Press, 1951.DiDio, L J A, Synopsis ofAnatomy. St. Louis: C.V Mosby, 1970,Dorland's Illustrated Medical Dictionary, 25m ed. Philadelphia:W B, Saunders, 1975,Freeman, A. A, R, Adult Articular Cartilage, London: PitmanMedical, 1973,Gray, H., Gray's Anatomy, 36th British ed. (P L Williams and RWarwick, eds.). Philadelphia: W B, Saunders, 1980,

Gray, H" Gray's Annunuy, 38t11British ed, London: Churchill andLivingstone, 1995.Guyton, A, c., Textbook of Medical Pbysiology, oth ed. Philadelphia:W, B. Saunders, 1981.

Henderson, 1. F, and J H, Kenneth, A Dictionary of ScientificTer111s,7th ed. Princeton, NJ: D, Van Nostrand, 1960.Hultkranz, W, "Uber die Spaltricbtungen del' Gelenleknorpel," Ver-handlungen der Anarornischen Gesellschafr. Aus der ZwolfenVesammlung in Kiel, 14 (Suppl.) 1898,Judson, L Y., and A T Weaver, Voice Science. New York: Appleton-Century-Crofts, 1965,Kuehn, D" M, Lemme, and J Baumgartner, Ne71TaI Bases ofSpeech-Hearing and Language, Boston: College Hill Press, 1989.

Love, R, ],' and W, G. Webb, Neurology f01' tbe Speecb-LanguagePathologist. Boston: Butterworth-Heinemann, 1992,

McCall, J G" "Scanning Electron Microscopy of Articular Sur-faces," Lancet, 1968,

Moore, c., The Correspondence of Vocal Tract Resonance withVolumes Obtained from Magnetic Resonance Images," J. Sp.H177g, Res, 35, 1992, 1009,Moore, K. L, Clinicaliy Oriented Anatomy, Baltimore: Williamsand Wilkins, 1985,Patten, B, M" Human Embryology, Philadelphia: Blakiston, 1946,Perlman, A., 1. Titze, and D, Cooper, "Elasticity of Canine VocalFold Tissue," J. Sp, Hrng. Res" 27,1984,212-219.Perrier, P, L. J Boe, and R Sock, "Vocal Tract Area Function Es-timation from Midsagittal Dimensions with CT Scans and a VocalTract Cast: Modeling the Transition with Two Sets of Coeffi-cients," J. Sp, Hrng. Res" 35, 1992,53-67,Woodburne, R T, Essentials of HU11lan Anatomy, New York: Ox-ford University Press, 1973,