In phonetics, the airstream mechanism is the method by which airflow is created in the vocal tract. Along with phonation, it is one of two mandatory aspects of sound production; without these, there can be no speech sound.
The organ generating the airstream is called the initiator; for this reason the production of airflow is called initiation. There are three initiators used in spoken human languages: the diaphragm together with the ribs and lungs (pulmonic mechanisms), the glottis (glottalic mechanisms), and
the tongue (lingual or "velaric" mechanisms).
Any of the three initiators − diaphragm, glottis or tongue − may act by either increasing pressure in the airstream or by reducing it with suction. These changes in pressure are often said to involve outward and inward airflow, and are therefore termed egressive and ingressive mechanisms; however, ingressive mechanisms often only reduce outward airflow, and even when air flows into the mouth, it always passes out past the glottis.
Of these six possible airstream mechanisms, four are found in words around the world: pulmonic egressive, where the air is pushed out of the lungs by the ribs and diaphragm. All human languages employ such sounds (such as vowels), and nearly three out of four use them exclusively. glottalic egressive, where the air column is pushed upward by the glottis. Such consonants are called ejectives. Ejective and ejective-like consonants occur in 16% of the languages. glottalic ingressive, where the air column is rarefied as the glottis moves downward. Such consonants are called implosives. Implosive and implosive-like consonants occur in 13% of the world's languages. lingual ingressive, AKA velaric ingressive, where the air in the mouth is rarefied by a downward movement of the tongue. These are the clicks. Clicks are regular sounds in ordinary words in fewer than 2% of the world's languages, all but one in Africa.
These mechanisms may be combined into airstream contours, such as clicks which release into ejectives.
The Khoisan languages have pulmonic, ejective, and click consonants, the Chadic languages have pulmonic, implosive, and ejective consonants, and the Nguni languages utilize all four, pulmonic, click, implosive, and ejective, in normal vocabulary.
In interjections, the other two mechanisms may be employed. For example, in countries as diverse as Canada, Sweden, Turkey, and Togo, a pulmonic ingressive ("gasped" or "inhaled") vowel is used for back-channeling or to express agreement, and in France a lingual egressive (a "spurt") is used to express dismissal. The only language where such sounds are known to be contrastive in normal vocabulary is the ritual language Damin; however, that language appears to have been intentionally designed to be different from normal speech.
Initiation by means of the lungs (actually the diaphragm and ribs) is called pulmonic initiation. The vast majority of sounds used in human languages are pulmonic egressives. In most languages, including all the languages of Europe (excluding the Caucasus), all phonemes are pulmonic egressives.
The only attested use of a phonemic pulmonic ingressive is a lateral fricative in Damin, a ritual language formerly used by speakers of Lardil in Australia. This can be written with the extended version of the International Phonetic Alphabet as [ɬ↓]. !Xóõ has ingression as a phonetic detail in one series of its clicks, which are ingressive voiceless nasals with delayed aspiration, [↓ŋ̊ʘʰ ↓ŋ̊ǀʰ ↓ŋ̊ǁʰ ↓ŋ̊!ʰ ↓ŋ̊ǂʰ]. Peter Ladefoged considers these to be among the most difficult sounds in the world. Other languages, for example in Taiwan, have been claimed to have pulmonic ingressives, but these claims have either proven to be spurious or to be occasional phonetic detail.
In interjections, but not in normal words, pulmonic ingressive vowels such as [ə↓] frequently occur in Scandinavian languages, e.g. Swedish, and contrary to the...
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