Articulation: the actions of the organs of speech in producing the sounds of speech.
Articulation disorder is defined as incorrect production of individual speech sounds, traditionally classified as substitution, omission and disortions errors. It can be classified as functional or organic in nature. An articulation disorder is considered functional when no known pathology is causing the errors. An organic disorder results from known physical causes, such as cleft palate, neurological dysfunction or hearing impairment. Some children may experience both functional and organic deficits.
The articulatory system consists of the following:
- Respiratory system: provides the airflow that creates sound. Sound is produced when the air stream is set into vibration by the vocal fold or the articulators. There can be no sound without vibrating air.
- Phonation (voice): provides the sound source for vowels and voiced consonants. A periodic complex sound wave is produced by the vibration of the vocal folds at the level of the larynx. As the sound leaves the vocal folds, it enters the resonance chambers of the pharynx, oral cavity and sometimes the nasal passages.
- Resonance: modifies sound waves coming from the larynx so that different speech sounds are produced. These differing sounds result from varying the size and shape of the vocal tract. For example, each vowel results from a different vocal tract size, shape and opening. Variations in the shape of the vocal tract are created by the movement of the articulators, primarily the tongue.
- In articulation, the movement of the articulators creates varying resonance characteristics and also creates other speech sounds by interfering with the flow of air through the vocal tract. When the airflow is completely interrupted and then released, or when it is restricted to create friction, characteristic speech sounds results.