Speech and Speech Disorders. Speech is a learned system of communication requiring the coordinated use of voice, articulation, and language skills. Although many animals are physiologically able to use the voice for communicating a wide range of simple messages to others of their species, only humans are able to produce true speech (as opposed to the skills in speech mimicry of such birds as parrots and mynae). In a broad sense, speech is synonymous with language.
Voice, or phonation, is the sound produced by the expiration of air through vibrating vocal cords (see Larynx). Voice is defined in terms of pitch, quality, and intensity, or loudness. Optimum pitch, which means the most appropriate pitch for speaking, varies with each individual. Both optimum pitch and range of pitch are fundamentally determined by the length and mass of the vocal cords; within these limits, pitch may be varied by changing the combination of air pressure and tension of the vocal cords. This combination determines the frequency at which the vocal cords vibrate; the greater the frequency of vibration, the higher the pitch.
Another aspect of voice is resonance. After voice is produced, it is resonated in the chest, throat, and cavities of the mouth. The quality of the voice is determined by resonance and the manner in which the vocal cords vibrate; intensity is controlled by resonance and by the strength of the vibrations of the vocal cords.
Articulation refers to the speech sounds that are produced to form the words of language. The articulating mechanism comprises the lips, tongue, teeth, jaw, and palate. Speech is articulated by interrupting or shaping both the vocalized and unvocalized airstream through movement of the tongue, lips, lower jaw, and soft palate. The teeth are used to produce some specific speech sounds.
IV LANGUAGE SKILLS AND OTHER FACTORS
Language is an arbitrary system of abstract symbols agreed upon by any group of people to communicate their thoughts and feelings. Symbols may be verbal or nonverbal, that is, either spoken or written; additionally, nonverbal symbols may be gestures and body movements (See also Sign Language). In spoken language the skills of articulation are used; in written language, spelling is substituted for articulation. Both auditory and visual skills are essential to the comprehension and expression of language.
Rate and rhythm also should be considered in the evaluation of speech. Connected speech should not be so rapid or so slow that it interferes with comprehension. Rhythm is judged mostly in terms of fluency. Good or so-called normal speech cannot be exactly measured or described, however; it can be judged essentially only as it seems to be suitable to the sex, size, age, personality, and needs of the speaker.
V SPEECH DISORDERS
Because speech is a learned function, any interference with learning ability may be expected to cause a speech impairment. The most common interfering conditions are certain neuroses and psychoses, mental retardation, and brain damage, whether congenital or acquired. Articulation itself may be impaired by such physical disabilities as cleft palate, cerebral palsy, or loss of hearing; it may likewise deteriorate as a result of paralysis of any part of the articulating mechanism. Impairment may also be the consequence of unconscious imitation of poor speech models or inadequate perception of auditory stimuli.
Voice disorders, so-called dysphonias, may be the product of disease or accidents that affect the larynx. They may also be caused by such physical anomalies as incomplete development or other congenital defect of the vocal cords. The most frequent cause, however, is chronic abuse of the vocal apparatus, either by overuse or by improper production of the voice; this may result in such pathological changes as growths on or thickening and swelling of the vocal cords.
Disorders of rate and rhythm are generally either psychogenic or have a basis in some neurological disturbance. A notable example of a neurological condition is Parkinson disease.
VI SPEECH THERAPY
A speech therapist is a specialist who has been trained to diagnose and treat the various disorders of speech, language, and voice. Because physical, neurological, or psychological conditions often are either responsible for or are related to the speech disorder, the therapist often works as a member of a team, which may include a neurologist, an otolaryngologist, a psychiatrist, a psychologist, a psychiatric social worker, and a speech pathologist.
Speech disorders caused by disease, injury, or malformation fall in the province of the physician and surgeon. Once these defects are remedied, the speech therapist is responsible for teaching the speech-impaired person to hear and monitor speech accurately, to think appropriately in verbal terms, and to exercise control over speech disordered by incoordination or emotional influences.
Inasmuch as a hearing loss (see Deafness) will prevent learning by imitation of essential speech patterns and sounds and prevent the individual from monitoring his or her own errors, one of the therapist's most valuable techniques is the measurement of hearing. Because intellectual capacity and the ability to handle language are closely related, the therapist must also understand how intelligence develops in a young child. The most obvious emotional speech disorder is stuttering, which is often caused by anxiety. The speech therapist uses a program of speech exercise to reduce this disability. Where necessary, the aid of a psychologist is enlisted; in extreme cases, a psychiatrist assists with psychotherapy.