Speech

Speech is the method by which humans express language using the voice. It is the most common way language is conveyed: a person produces sounds (phonemes—the smallest units of sound that distinguish meaning), which combine into words and sentences. Speech differs from language in general, since language can be transmitted in other ways, such as writing or sign language for the deaf.

Speech is often compared with hearing: speech is a two-way process consisting of production and reception. The speaker transforms air from the lungs into sound waves; the listener interprets those waves using linguistic knowledge they already possess.

The physiological mechanism of speech

Speech begins with air expelled from the lungs. As this air passes through the larynx, it causes the vocal cords to vibrate, producing fundamental sound. Subsequently, the upper speech organs—the tongue, lips, teeth, and palate—shape the various sounds. The position of the tongue and the opening of the mouth distinguish consonants from vowels.

Branches of study

Phonetics studies the sounds of speech as they are—their production, movement through the air, and how the ear receives them. Phonology examines how sounds function as a system in a particular language and the rules of change among them. Other fields such as psycholinguistics investigate how the brain plans and produces speech.

Language acquisition in children

Infants begin with sound-making and repetition of sounds (babbling) before producing words. This is followed by single-word utterances, then combining two words, until reaching complete sentences. The pace of acquisition varies from child to child, but the general sequence of developmental stages is similar across the world's languages.

Speech disorders

Various conditions affect speech, including stuttering (difficulty in the flow of speech), sound disorders, and aphasia—a language impairment resulting from brain injury. People for whom speech is difficult can use assistive devices that convert text to sound, or sign language.