An airstream mechanism is a body of air which is used for speech production. An airstream mechanism is like a syringe fitted with plunger. The plunger functions as an initiator with which one can draw in or put out fluid from the syringe.
There are three types of Airstream Mechanism :
Pulmonic, Glottalic and velaric. Each airstream mechanism involves both egressive and ingressive action.
An egressive action involves the pushing out of air, while the ingressive action involves the sucking in of air.
Let us briefly examine the three types of Airstream Mechanism one by one.
Pulmonic Airstream Mechanism
The initiator of the Pulmonic airstream mechanism is the lungs and its associated muscles, including the diaphragm.
The diaphragm is muscle band that separates the chest cavity from the stomach.
It interacts with the intercostal muscles to cause an expansion or contraction of the chest cavity, and allows air to flow in from the higher pressure region of the atmosphere.
A contraction produces higher pressure in the chest cavity and results in an outflow of air.
There are two types of Pulmonic airstream mechanism :
Pulmonic egressive and Pulmonic ingressive
The Pulmonic egressive is a body of air expelled from the lungs. It is generally the used for talking and singing.
All English sounds are produced using the Pulmonic egressive airstream mechanism, and all sounds produced with the lungs as the initiator are called Pulmonic sounds.
Most human speech sounds are produced with the Pulmonic egressive airstream mechanism.
The Pulmonic ingressive airstream mechanism is hardly used in sound production.
It is in non-linguistic acts such as yawning, or most kinds of snoring.
Glottalic Airstream Mechanism
The closed glottis is the initiator of the glottalic airstream mechanism.
If the closed glottis is moved upwards, air is compressed in the mouth above the glottal closure causing an outward movement of air .
This outward movement of air known as the glottalic egressive airstream mechanism.
Sounds produced with the glottalic egressive airstream mechanism are called Ejectives.
Ejectives are found in Hausa. They are written phonetically with an apostrophe.
Examples [ p’ , t’ ,k’].
On the other hand, if the closed glottis is moved downwards, the body of air that is built above the closed glottis is drawn in when the glottis eventually opens.
The inward movement of air is known as the glottalic ingressive airstream mechanism.
The sounds produced with the glottalic ingressive airstream mechanism are called implosives. Example [ ɓ, ].
Velaric Airstream Mechanism :
The velaric airstream mechanism involves raising the back of the tongue in firm contact with the velum (the soft palate).
The initiator of this airstream mechanism is the closure formed by raising the root of the tongue against the velum.
This contact can be used to pushed out air from the mouth or to suck in air.
When air is pushed out, we refer to this type as a velaric egressive airstream mechanism does not seem to be used to produce any human speech sound.
The velaric ingressive airstream mechanism is used for the production of click sounds. Clicks are found in the some Bantu languages such as Xhosa and Zulu, and also in the languages of the Bushman and Hottentots.