Terms applied to the sounds produced in the upper AIR PASSAGES which form one of the means of communication between human beings. Air passes through the LARYNX to produce the fundamental notes and tones known as voice. This is then modified during its passage through the mouth so as to form speech or song.
This has three varying characteristics: loudness, pitch, and quality or timbre. Loudness depends on the volume of air available and therefore on the size of the chest and the strength of its muscles. Pitch is determined by larynx size, the degree of tenseness at which the vocal cords are maintained, and whether the cords vibrate as a whole or merely at their edges. In any given voice, the range of pitch seldom exceeds two and a half octaves. Typically, the small larynx of childhood produces a shrill or treble voice; the rapid growth of the larynx around PUBERTY causes the voice to ‘break’ in boys. Changes in the voice also occur at other ages as a result of the secondary action of the SEX HORMONES. Generally speaking, the adult voice is bass and tenor in men, contralto or soprano in women. Timbre is due to differences in the larynx, as well as to voluntary changes in the shape of the mouth.
Rapid modifications of the voice, produced by movements of the PALATE, tongue and lips. Infants hear the sounds made by others and mimic them; hence the speech centres in the BRAIN are closely connected with those of hearing.
See below, and also SPEECH DISORDERS.
or absence of the power to speak, may be due to various causes. LEARNING DISABILITY may prevent an infant from mimicking the actions of others; or the child has normal intelligence but some neurological disorder, or disorder of the speech organs is responsible. Complete DEAFNESS or significant early childhood ear disease may be the cause. SELECTIVE MUTISM (also termed elective mutism) represents a situation where the child will talk normally in some circumstances, for example with a parent at home, but is totally silent in any situation which is unfamiliar or which creates anxiety – even in some cases simply attending school.
is a highly individual condition, but is basically a lack of coordination between the different parts of the speech mechanism. (See also main entry on STAMMERING.)
is the inability to speak or understand speech, most commonly following brain disease, such as STROKE.
or loss of voice may be caused by LARYNGITIS or, rarely, a symptom of conversion and dissociative mental disorders – traditionally referred to as HYSTERIA. It is generally of short duration.