Speech production mechanisms and processes

Speech Production

The formation of speech actually begins in the brain as described by Fernando Trujillo. After the creation of a message and the lexico-grammatical structure (a combination of vocabulary and grammar) in our mind, we need a representation of a sound sequence and a number of commands which will be executed by our speech organs to produce speech. These are referred to as a phonetic plan and a motor plan, respectively. Next, speech is produced through four processes: 1) initiation, 2) phonation, 3) oro-nasal process and 4) articulation.

Giegerich (1992) describes the initiation phase. In this phase, air is exhaled from the lungs. This air stream serves as the source of energy for speech. For speaking in English, the air stream moves out of the lungs and through the trachea. The air stream then passes through the larynx at the upper end of the trachea which contains folds of tissue called vocal folds.

Between these folds lies the glottis.

The glottis, according to Giegerich (1992), is where the phonation phase occurs. Speakers manipulate their vocal folds and thus, the glottis into different positions to make sounds. There are three significant positions, closed, narrow and open:

Closed where the vocal folds are brought close together to prevent air from passing between them. This produces what is called a glottal stop heard in English before a forcefully pronounced vowel; an example is 'Out!'

Narrow where there is an only a small gap for the air stream to pass through so that the passage of air makes them vibrate. This vibration of the vocal folds causes the air column above the glottis to vibrate. This produces what is known as voiced sounds like vowels and letters such as 'm',' l', 'v', and 'b'.

Open where the glottis is open wide enough to allow the air stream to pass unobstructed. In this way, voiceless sounds are produced. Examples include the 'st' sequence in the word 'stone' and the 'k' in kill.

The vocal tract consists of three joined cavities: the oral cavity, the nasal cavity, and the pharyngeal cavity. The surfaces and boundaries of these cavities are known as the organs of speech. What happens to the air within these cavities is known as the oro-nasal process (Articulatory phonetics). Through the oro-nasal process we are able to differentiate between similar nasal consonants such as 'm' and 'n' and other sounds (Trujillo).