Anatomy, Physiology, and Pathology of the Organs of Hearing, Vision, and Speech - A. G. Shvetsov 2006

Anatomy, Physiology, and Pathology of Voice and Speech Production
Voice Production (Physiology of Speech)

Spoken speech is the result of the sequential interaction of four articulatory processes:

1. The formation of an airstream, which is generated when air is forcefully expelled from the Lungs;

2. The process of phonation (voicing), when the airflow begins to vibrate as it passes through the vocal cords;

3. the process of articulation proper, when the vibration in the airstream is shaped by resonators formed in the oral and nasal cavities by the Organs of articulation;

4. the propagation of a specifically shaped sound wave into the environment.

Speech production is closely linked to breathing. Speech is produced during the exhalation phase, during which the airstream simultaneously performs voice-producing and articulatory Functions. Breathing during speech differs significantly from quiet breathing when a person is silent. Naturally, a longer exhalation requires a larger supply of air. Therefore, during speech, the volume of inhaled and exhaled air increases significantly (by about 3 times). Inhalation during speech becomes shorter and deeper, while exhalation is much longer (5 to 8 times) than inhalation (whereas during quiet breathing, the duration of inhalation and exhalation is approximately equal) and is carried out with the active involvement of expiratory Muscles (the abdominal wall and internal intercostal muscles). This ensures its maximum duration and depth and, furthermore, increases the pressure of the airstream, without which voiced speech is impossible. In addition, during speech, the respiratory rate is halved (8–10 breaths per minute) compared to quiet breathing (16–20 breaths per minute).

The characteristics of speech breathing are presented more clearly in Table 1.

Class="center">Table 1. Characteristics of speech breathing

During quiet breathing, the glottis is wide open and shaped like an isosceles triangle. Inhaled and exhaled air passes silently through the wide glottis. During phonation (voicing), however, the vocal folds are adducted (closed) (Fig. 21). The stream of exhaled air, forcing its way through the closed vocal folds, pushes them slightly apart. Due to their elasticity, as well as the action of the laryngeal muscles that constrict the glottis, the vocal folds return to their initial, i.e., medial position, only to be pushed apart again by the continuous pressure of the exhaled airstream, and so on. This cycle of opening and closing continues until the pressure of the voice-producing expiratory airstream ceases. Thus, phonation involves the vibration of the vocal folds. These vibrations occur in a transverse rather than longitudinal direction, meaning the vocal folds move medially and laterally (inward and outward), rather than upward and downward.

Fig. 21. Diagram of vocal fold action: A — during breathing; B — during voice production (phonation)

As a result of the vibration of the vocal folds, the movement of the exhaled airstream is converted above the vocal folds into the vibration of air particles. These vibrations are transmitted into the environment and are perceived by us as vocal sounds.

However, the Larynx alone cannot produce a specific speech sound; it is formed not only in the larynx but also in the so-called resonators, which shape the loudness and clarity of speech sounds. The resonators are located in the vocal tract — the part of the respiratory-digestive tract located above the larynx: the Pharynx, oral, and nasal cavities. Changes in the shape and volume of the vocal tract produce Resonance phenomena, as a result of which some overtones of speech sounds are amplified while others are dampened. Thus, a specific speech sound spectrum emerges, characterized by intensity, pitch, and timbre.

Vocal intensity depends mainly on the amplitude of the vocal fold vibrations, which is determined by the level of air pressure (i.e., the force of exhalation), as well as the Influence of the resonating cavities of the vocal tract, which act as sound amplifiers.

The size and shape of the resonating cavities, along with the Anatomical Features of the larynx, influence the individual "color" of the voice, or timbre. It is because of timbre that we can distinguish people by their voices.

Vocal pitch depends on the frequency of vocal fold vibration, which, in turn, depends on their length, thickness, and tension. The longer, thicker, and less tense the vocal folds are, the lower the pitch of the voice. In addition, vocal pitch depends on the pressure of the airstream on the vocal folds and the degree of their tension.

The unique feature of the human vocal tract, compared, for example, to the pipe of a wind instrument like an organ, is that it not only amplifies the voice and gives it an individual quality (timbre) but also serves as the site where speech sounds are produced.

The Russian language has a fairly rich system of phonetic resources—42 distinct sound types, including 6 vowels and 36 sonorants and obstruents, voiced and voiceless consonants. In the pronunciation of Russian sounds, the larynx and the laryngeal part of the pharynx are practically uninvolved (unlike in Caucasian languages), nor are labiodental combinations (typical of English), diphthongs, double vowels, or the intermediate sound between 'a' and 'e' (typical of Baltic languages). However, considering that there are languages with a very concise system of speech sounds (down to 15 in some African languages), the Russian phonetic system can be considered quite rich. During The production of speech sounds, the vocal tract functions as a noise vibrator (while the vocal folds in the larynx function as the tone vibrator). The noise vibrator consists of the constrictions between the Lips, the Tongue and Teeth, the tongue and hard palate, the tongue and alveoli, the lips and teeth, as well as the occlusions between these organs that are broken by the airstream and created by various Movements of the tongue and lips. Voiceless consonants—those produced without voicing—are formed using the noise vibrator, while the simultaneous activation of the tone vibrator (vocal fold vibration) produces voiced consonants (formed by noise accompanied by voicing) and sonorants (formed by voicing with minimal noise—m, n, l, r).

Most non-sonorant consonants are paired as 'voiced–voiceless': p–b, f–v, sh–zh, etc. Unpaired voiceless consonants are kh, ts, ch, shch, and the unpaired voiced consonant is j (yot).

The activity of the active organs of speech (the lower jaw, lips, tongue, and soft palate) is called articulation and ensures the production of speech sounds proper. The Oral Cavity and pharynx participate in the pronunciation of all Russian sounds, and each vowel sound corresponds to a specific configuration of the active organs of speech—the tongue, lips, and soft palate. For example, when pronouncing the sound 'a', the oral cavity expands, while the pharynx constricts and elongates. Conversely, when pronouncing the sound 'i', the oral cavity constricts, and the pharynx expands. As a result, the same sound generated in the larynx acquires a quality characteristic of a particular vowel in the vocal tract, primarily in the oral cavity. In this process, the forward and backward movements of the tongue, as well as its varying degrees of elevation toward a specific part of the palate, alter the volume and shape of the resonating cavity. The lips, by protruding and rounding, form the opening of the resonator and elongate the resonating cavity.

With correct pronunciation, the nasal resonator is involved only in the production of the sounds 'm' and 'n' and their palatalized (soft) variants. During the pronunciation of all other sounds, the velum (formed by the soft palate and the uvula) closes the entrance to the Nasal cavity, preventing it from participating in sound production. Thus, the first section of the peripheral speech apparatus serves to supply air, the second to produce voice, and the third acts as a resonator that gives the sound its intensity and quality, thereby forming the characteristic sounds of our speech resulting from the activity of individual active Organs of the articulatory apparatus. However, for words to be pronounced in accordance with the intended message, the Cerebral Cortex selects commands to organize speech movements. These commands are called the articulatory program, which is implemented in the executive part of the motor speech analyzer—namely, the respiratory, phonatory, and resonatory systems. Speech (articulatory) movements are executed with such precision that they result in specific speech sounds and form spoken (or expressive) speech.