Applying Phonetics. Murray J. Munro

      As discussed in Chapter 1, articulatory phonetics is the study of how humans use the vocal tract to produce speech. You don't need a highly detailed knowledge of speech anatomy to grasp the major issues in speech science. However, to understand many of the uses of phonetics, it is helpful to gain a basic familiarity with the major structures of the vocal tract and to understand their functions. This chapter presents an overview of the fundamentals of speech anatomy in order to prepare you for the material that follows in later chapters.

2.1 the vocal apparatus

Though we tend to think of spoken language as a key aspect of our humanness, it is striking that our bodies appear to contain no structures that are used uniquely for speech. In fact, every component of the human vocal apparatus exists because of its role in some more basic, survival‐oriented function. Our “organs of speech” therefore illustrate an evolutionary phenomenon called EXAPTATION: the recruitment of old structures for new purposes. Several examples are given in Table 2.1. The lungs, for instance, which initiate the airflow for most speech, are essential for the life‐supporting function of pulmonary ventilation (breathing). The teeth and tongue, which we use to articulate many speech sounds, are needed for mastication (chewing) and—along with parts of the LARYNX—for deglutition (swallowing). Olfaction (smelling) occurs through structures in the NASAL CAVITY, which also happens to allow production of speech sounds like the /m/ in mouth. Together, structures of the nose and tongue make gustation (tasting) possible. And the VOCAL FOLDS (popularly known as the vocal cords) help guard the TRACHEA (windpipe) from food and liquids that might pose serious problems should they enter the lungs. All these parts of the vocal tract exist in many non‐human—and therefore non‐speaking—animals, so they are clearly not specific to speech.

      The term exaptation was coined by Stephen Jay Gould and Elisabeth Vrba, two American paleontologists who studied how traits and structures often develop new functions that differ from their original ones.

Table 2.1 Exapted Structures Used for Speech

2.2 making speech

In the 1960s, Peter Denes described the processes of speech production and perception as a “speech chain” connecting the speaker and the listener (Denes & Pinson, 1993). The links in the chain are at multiple levels: linguistic, physiological, and acoustic (see Figure 2.1). Before we utter anything, we must have something in mind to say. As we develop an idea, we use our linguistic capabilities to choose the necessary words or lexis from our mental dictionaries and to encode our message grammatically by formulating phrases and sentences. Physiology comes into play as the brain begins sending motor commands to the appropriate structures in the vocal tract, such as the vocal folds, tongue, and lips. Notice that the linguistic and physiological processes can overlap: the speaker may produce an utterance while still planning more speech. The activity of the vocal structures yields a complex acoustic signal that travels through the air to the listener's ears. There the decoding process occurs. First the listener's perceptual system converts the sound to neural signals—another physiological process—and then these are interpreted as words, phrases, and sentences, again on the basis of linguistic knowledge.

      For the moment, we will focus on three major aspects of the physiological part of the sequence: initiating the airstream, PHONATION, and ARTICULATION.

      2.2.1 initiating the airstream

Humans create most speech by exploiting the outgoing airstream during pulmonary ventilation. The structures used for this purpose are shown in Figure 2.2. During the process, carbon dioxide and oxygen are exchanged in the lungs through a two‐phase cycle of inspiration and expiration. To initiate typical inspiration, the diaphragm is lowered, causing the thoracic cavity—the chest—to expand. As a result of the increase in available volume, air pressure in the chest drops, and air rushes in through the nasal cavity to fill the lungs. The reverse phase, expiration, is partly caused by relaxation of the diaphragm, which decreases the size of the chest cavity. This increases the thoracic air pressure so that air moves outward. Most speech is produced using this outward airflow and is therefore said to entail a PULMONIC EGRESSIVE airstream. By this, we simply mean that the source of airflow for the speech is the lungs (pulmonic), and the direction of the flow is outward (egressive).

Figure 2.1 The “chain” connecting speaker and listener during speech