Psysiological, acoustic and auditory aspects of speech

Articulatory phonetics studies the way speech sounds are made (articulated).

Acoustic phonetics studies physical properties of speech sounds as transmitted between mouth and ear.

Auditory phonetics studies the perceptual (vjemovou) response to speech sounds.

Physiological aspect of the speech

The organs that are used for communication are called organs of articulation or articulators. They can be divided into 4 main groups.

1. Respiratory organs (lungs, trachea)

2. Phonatory organs (vocal cords)

3. Resonating cavities (oral and nasal cavities)

4. Modulating organs (lips, teeth, tongue, alveolar ridge, palate)

Respiratory organs

The main source of energy for the production of speech sounds comes from the lungs. Depending on the way the air is released from the lungs we can distinguish between these air stream mechanisms:

Pulmonic = sound which is produced by the energy of the lungs. It can be egressive (the air is expelled from the lungs, we breathe out) or ingressive (the air is breathed in inside the lungs)

Phonatory organs

Within larynx there are two thick flaps of muscles which look rather like a pair of lips, they can be brought together or parted through muscular tension. These organs are called vocal cords. The process of passing the air stream through the vocal chords resulting in audible vibration is called voicing – phonation. The opening between vocal cords - glottis - can assume different positions of openness:

Wide apart – glottis is fully open, production of voiceless consonants

Loosely together – glottis is slightly open, production of glottal fricatives

Loosely together and vibrating – the air causes vibrations, voiced sounds

Tightly closed – no air comes out or in, production of glottal stop

Resonators

Resonants include oral cavity and nasal cavity. The air stream comes from the lungs and passing through the pharynx can be in one of these three ways:

The soft palate is lowered and the oral cavity is blocked - the air escapes through the nasal cavity. This is where we produce nasal sounds m, n.

The soft palate is raised and blocks the nasal cavity - we produce oral sounds g, f, a, b.

Modulating organs

a) Teeth – produce dental sounds / ð, θ /

b) Alveoral ridge – alveoral sounds /s, z, t, d, r, l /

c) Hard palate – we produce palatal sounds / j /

d) Tongue – lingual sounds

e) Lips – labial, bilabial or labial-dental sounds / p, b, m /

f) Soft palate = velum – veral sounds / k, ch, n /

Acoustic aspects of the speech

The air contains of particles which are in a constant movement, these particles create certain air pressure. When the vocal cords start vibrating they cause fluctuations of the air pressure, these fluctuations spread in all directions and become less intensive with bigger distance from the source.  The wave created by compressing and expanding of the air carrying a sound is called a sound wave – amplitude. When the air comes out of the oral cavity, the vibrations we hear are of 2 types:

Regular (periodic) vibration is produced by vocal cords providing that they are vibrating at the constant frequency and with constant intensity. Periodic vibration equals periodic wave. Periodic waves consist of certain wave patterns that periodically (at equal intervals) repeat themselves. There are two types of periodic waves:

Simple periodic wave is almost non-existent in domain of naturally produced sounds. Complex periodic wave is a wave in which simple sine waves are combined into one single wave, sounds produced by the vocal cords are usually of this type.

Irregular (aperiodic) vibration do not show a regular periodic pattern, they are composed of a large number of sine waves of different frequency and intensity, there is no repetition of any pattern, no regularity. All voiceless fricatives, voiceless affricates and plosives are aperiodic waves.

Vowels – periodic sounds with regular pattern of vibration

Fricatives – voiceless: aperiodic sounds  / voiced : combine aperiodic with periodic sounds

Nasals – periodic

Affricates – voiceless affricates : silenced and aperiodic  / voiced: mixture of periodic and aperiodic

Approximants – periodic

Plosives – voiceless, aspirated: aperiodic   / voiced: periodic

Auditory aspects of speech

It focuses on perception of sounds and the way they are heard and interpreted, deals with the listener who receives message from the speaker. The majority of processes of auditory aspects concern the brain in which the sound is decoded. Before the sound is processed by brain it encounter the ear. The basic function of the ear is a perception of auditory stimulus and its analysis and transmission further on to the brain.

Outer ear is represented by the pinna or auricle (the only visible part) and outer ear canal. Auricle plays protective role for the rest of the ear and helps to localize sounds, outer ear canal functions as protection for middle ear and as resonators for the sounds.

Middle ear is a cavity containing miniature structures that are important for audition. One of them is the eardrum – a membrane to which sounds are directed causing vibrations and thus transmitting incoming sounds. Middle ear also contains tiny bones – mallet, anvil and stirrup – which move by the vibrations caused by eardrum. In the middle ear there is also Eustachian tube that is connected with pharynx to help preserve a required amount of air pressure inside the middle ear.

Inner ear includes cochlea – a cavity with liquid, at each ends of cochlea there is an oval window. Inside cochlea there are two membranes – vestibular and basilar which play central role in audition, there is also the organ of Corti – a real auditory receptor.

Transmission

Sound goes through auricle and outer ear canal to middle ear where vibrates the eardrum and the small bones – the movement is then transmitted by oval window to the liquid in cochlea. Liquid vibrates the membranes inside cochlea and the cells of organ Corti detect the movements and convert them into neutral signals that are transmitted via nerves into the brain.

The way in which human brain processes auditory information and links it to the speech is unknown. What is clear is fact that human ear can only hear sounds having certain amplitudes and frequencies. Lower frequencies are not heard and higher are giving us a sensation of pain. Brain decodes, classifies, interprets and arranges the individual sound according to the linguistic patterns already existing in mind.