Language Disorders

Human communication and socialization to a large degree occur through language, which is a symbol system used to represent, convey, and interpret ideas, thoughts, and feelings. Typically one language user (a sender) arranges words or other vocabulary symbols (e.g., gestures, as used in sign language) to express particular intentions or ideas to at least one other language user (a receiver). While many equate language with speech, they are not identical. Speech, along with writing and pantomime, is just one of the channels used to express language. Language is understood through reciprocal channels, like listening, reading, or interpreting manual signs.

Language involves a number of interactive systems related to its content, form, and use. Semantics refers to a system of concepts or meanings. The "mental dictionary" that contains vocabulary symbols for expressing and interpreting these concepts is called the lexicon. Morphology is concerned with word formation. Morphemes, the smallest units of language that signal meaning, can be single words or they can be add-ons, like possessive or past tense markers, that change the meaning of their root words. Phonology refers to the sound system of language (vowels and consonants), and to stress and melody patterns. Although phonology is most obviously connected with the speech channel, there is ample evidence that adults also access phonology when they read silently. Syntax involves the ways that words representing different parts of speech can be sequenced to construct acceptable and interpretable phrases, clauses, and sentences. To illustrate, English syntax allows only certain combinations of nouns and verbs (e.g., "The girl ate" is acceptable, but "Ate the girl" is not); and different word orders signal different meanings (compare "The girl told the boy" with "The boy told the girl"). Finally, pragmatics is concerned with the ways in which language is used to communicate particular purposes and intents. For example, pragmatics involves the difference between what someone actually says and what they mean by it, as when teasing or being sarcastic. The particular communicators, their shared assumptions and knowledge, and their current social context all are important pragmatic considerations.

Language disorders can take the form of difficulty expressing and/or understanding ideas and intentions through any or all language channels, and can be reflected in disturbances of any or all language systems. Because language is not identical to speech, language disorders are different from speech disorders. The latter may reflect, among other things, abnormalities in vocal tract structures such as the lungs, larynx (commonly known as the voice box), and oral articulators (e.g., tongue, lips, jaw), or difficulties in managing the breathstream, which provides the energy source for speech.