Human speech makes possible the expression and communication of thoughts, needs, and emotions through vocalization in the form of words. It is a process whose specialized adaptations differentiate it from the mere making of sounds–a capacity humans share with most animals. In addition to the capacity for laryngeal production of sound (which some animals also possess), speech requires a resonance system for modulation and amplification of that sound and an articulation process for the shaping of that sound into the communally established word-symbols of meaning that constitute the language of a given culture. (Dean Edell) The use of language is made possible by certain cerebral functions: the formation of thoughts; the comprehension, storage, and recall of words; and the selection of words to express the thoughts and the arrangements of these words in a sequence or organization that constitutes (or attempts to constitute) intelligible communication.
The speech process involves the speech centers of the brain, the respiratory center in the brain stem, the respiratory system, the chest cavity, the structures of the larynx, the pharynx, the nose and nasal cavities, and the structures and parts of the mouth and related facial muscles. There are three identified speech areas. The Supplementary motor cortex, on the very top of the left frontal lobe, involves the process of vocalization itself. Broca’s area, lower down at the back of the left frontal lobe, appears to involve functions of articulation, vocabulary, inflection, and word sequence. Wernicke’s area is mainly the posterior part of the left temporal lobe, with parts of the parietal area; any large destruction of this area results in the loss of the capacity for meaningful speech but not the loss of sound production.
The speech process starts with an expiration of air, produced by the respiratory mechanisms of lung expansion and contraction: the downward and upward movements of the diaphragm to lengthen or shorten the chest cavity, and the elevation and depression of the ribs to increase or decrease the diameter of the chest cavity. These movements depend on the functions of the upper abdominal muscles. Overall, the muscles that elevate the chest cage are muscles of inspiration (inhalation), and those that depress the chest are muscles of expiration (exhalation). (Health Central) If forceful expiration is required, relative to body or speech needs, all abdominal muscles combined can serve as muscles of expiration. Expiration can then be passive or it can be forcefully active, depressing the cage and starting a current of air upward from the lungs. The driving energy for speech production, generated by the mechanisms of expiration, varies with individual physiology, breathing habits, and training for correction where needed.
The resonance process, which is fundamentally the amplification of sound on its way to utterance, involves he pharynx, the mouth, the nose, the nasal sinuses, and the chest cavity. The quality of that resonance, which may range from stridency to virtual inaudibility, also depends on both fixed and variable factors, with regard to physical conditions and learned behaviors, and relates to the intent of the individual and his or her personality as well as his or her speech behaviors. It also relates to the force of the expiration of air and the dimensions of the chest cavity. Through all the various effects and usage of these parts of the resonance mechanisms, certain types of speech mannerisms are exhibited–such as nasality, which represents over reliance on the nasal cavities for resonance; or good sound projection, which utilizes the chest cavity as well as the other organs. The process of articulation constitutes the formation of the amplified sound into words, through movements of the lips, tongue, and soft palate of the mouth, and of the related facial muscles. Moreover, the qualities of a given language may require different forms of articulation because the linguodental zone (between the tip of the tongue and the teeth) may be used differently in one language than the way it is in another.
Speech disorders, both functional and organic, at the handicap level, affect about 22 million persons in the United States, according to U.S. Public Health Service estimates. Approximately 40% are due to hearing loss, approximately 10% to neurological disease, and approximately 50% to a range of other causes. (Health Central) The highest incidence of speech disorders occurs developmentally among children and youth; functional disorders in articulation are the leading cause, stuttering is the second, and hearing impairment with speech defect is the third.( Dean Edell) Voice disorders, or dysphonias, consist of two main types: those arising from faulty speech habits, and psychogenic types arising from emotional disturbance. Both types represent either overactive) muscular activity, creating harsh, grating speech, or underactive activity, creating subdued or sluggish speech. Speech impediments include the following three types. Cluttering is an erratic, jerky speech.
Lisping, or immature speech, may relate to abnormality of the external speech organs, for example, in tongue-teeth relationships. stuttering, once considered a psychogenic disorder, is now thought to be caused by neurological deficiencies present at birth or caused by injury. Language disorders may lie between the functional and The organic, depending on the diagnostic assessment of the underlying cause. For example, if schizophrenia is viewed as an organic disorder, then its bizarre language is organically related. Similarly, the disturbed speech of mental retardates may be an organic behavior if the retardation can be attributed organically, or it may be a learning disability arising from the intellectual impairment. Other functional disorders include those caused by sensory deficits in the family setting, such as the presence of deaf parents; delayed maturation of motor or brain function; emotional trauma due to parental neglect or abuse; and institutional deprivations or adverse socioeconomic factors, which result in learning disabilities related to the development of speech or such disabilities as the improper formation of word sequences.
Genetic defects and hereditary diseases include Structural abnormalities of any of the organs related to Vocalization and are frequently exemplified by cleft lip or cleft palate; hereditary diseases of the muscular system, such as muscular dystrophy, or of the nervous system, such as ataxia; chromosome aberrations, such as Down’s syndrome (mongolism), which are associated with mental retardation; organic brain injury (genetic or birth defects); and hearing and related sensory losses. (Dean Edell)Developmental disabilities represent a large and serious group of organic diseases and disorders that affect the development of speech, either directly or through learning disabilities that affect, physically or intellectually, the normal maturation of speech. Major disorders in this area are cerebral palsy and the associated speech disorder; epilepsy and the related convulsive seizures; damage, by injury or disease, to any of the parts involved in articulation; the learning impairments of organic mental retardation; sensory losses, auditory and visual; and other types of brain damage due to injury or disease.
Speech center trauma in the brain occurs in two categories: damage to the speech centers and related sensory aspects of speech function (sensory aphasia); and damage to the motor control functions of the speech centers (motor aphasia). (Health Central)The basic aspect of aphasia–whether due to stroke, paralysis, head injury, or disease–is the loss of the capacity for the meaning of language or its comprehensible organization into words or word sequences. In other cases the intellectual functions appear to be retained, whereas the vocalization system cannot be utilized to emit words but rather only sounds.