The Anatomy of the Supralaryngeal Structures
The first two modules addressed the building blocks of speech--respiration, the force that drives speech, and phonation. This module will look at how sound is modified as it goes through the vocal tract.
The vocal tract is a resonating system. Some call it the supraglottal tract or upper airway. You can see a cross-sectional view of the vocal tract on page 89 in your textbook, figure 5.1, as well as in the picture tothe right. The vocal tract is a tube, approximately 17 centimeters in length in adult males. Structures in the vocal tract form a series of valves that change the shape of the tract to produce different sounds. The moveable articulators--the lips, tongue, and velum--act as valves to close or constrict the tube to produce speech sounds.
Some consider the vocal folds to be articulators. The vocal folds convert air pressure to sound by generating a periodic sound wave. Remember that the waveform of a periodic sound looks something like this. The vocal folds can make aperiodic sounds as well, such as when the vocal folds are partially adducted, making the breath stream turbulent. We see this in whispered speech and in the phoneme /h/. There are other sources of aperiodic sounds--releasing a voiceless stop for example. This sound is called a plosive because of the sudden release of pressure. You can also generate aperiodic sound by forcing the airstream through a constriction formed by the articulators. One example is a fricative, such as the first sound in "shoe." We also have sounds that are both periodic and aperiodic. Any time the vocal folds are vibrating, they add periodicity. One example is a voiced stop, such as /b/. Your text has a table of periodic and aperiodic sounds, found on page 116, table 6.1.
The picture on the left, which also appeared in the respiration module, is a schematic of the structures that modify airflow.
The supraglottal structures provide the final shaping fo the various speech sounds. Withouth these structures, the only differentiataion of sound would be due to vocal fold activity--whether a sound was voiced or voiceless, as well as pitch and loudness. The supraglottal structures allow for the production of a large number of speech sounds.
The resonatory cavities
There are three major chambers, or cavities in the resonatory system. The first is the pharyngeal cavity, or pharynx, which is just above the larnynx. It leads to the larynx and esophagus. It is the posterior part of the vocal tract. There are three parts of the pharynx. The lowest is the laryngopharynx, the middle is the oropharynx, and the upper is the nasopharynx. As you can see by the picture on the left, these parts are named according to which cavity they are near.
The second major cavity is the oral cavity, bounded by the teeth, the hard palate, and the soft palate, or velum. The anterior entrance to the oral cavity is through the lips, and the posterior part leads to the pharynx.
The third major cavity is the nasal cavity, which is a paired cavity. The nasal septum separates the two cavities and there are three nasal turbinates inside. The anterior entrance is through the nostrils, and the posterior part of the nasal cavity is the nasopharynx. The nasal cavity can be closed off from the pharynx by the elevation of the soft palate (velum). Minor cavities are the buccal, or cheek cavity, and the paranasal sinuses. These are located in the skull and lead to the nasal cavities--the sphenoid and ethmoid. These cavities are very small.
How do the resonatory cavities change shape?
The pharynx, oral cavity and nasal cavity are collectively referred to as the vocal tract. The shape of the tract determines which sound will be produced. Let's look at how these cavities change shape. The nasal cavities and the paranasal sinuses do not change shape, and they can be completely closed off through the velum. The pharynx is capable of changing sape to some degree; it has its own musculature. Page 90 in your text shows the three muscles of the pharynx, named because of their positions: superior, middle, and inferior constrictor muscles. The inferior constrictors are at the level of the pharynx, the middle is at the level of the hyoid bone at their most inveror aspect, and the superior constrictors form the bac of the pharynx from the level of the palate ot the mandible. Contraction of the constrictor muscles narrows the pharyngeal cavity, and relaxation of the musles widens it. The oral cavity is capable of changing shape a great deal by the positioning of the tongue, jaw, and lips. And of course, the tongue can change shape, too.
Articulation is the positioning of the speech structures. It influences resonation because it changes the shape of the vocal tract. "Articulate" means to bring together or join. With articulators, either the moveable structure is important--for example, with vowels, the tongue is important, and with bilabials, the lips--or they work in conjunciton with immovable structures. A couple of examples are the alveolar sounds, or the fricatives, which need a tight constriction. Do the following sorting activity to identify the moveable and immoveable supraglottal structures. Also review the structure of the articulators in your textbook pages 90-93.