Above the larynx, places of articulation in frequent use are between the back of the tongue and the soft palate, between the blade of the tongue and the ridge just behind the upper front teeth, and between the lips. Stoppage and release (technically, plosion) at these places form the k (often written as c, as in cat), t, and p sounds in English and, when voicing is also present, the g (as in gift), d, and b sounds. Obstruction at these and other places sufficient to cause noise gives rise to what are called fricative sounds; in English these include the normal pronunciations of s, z, f, and v and the th sounds in “thin” and “then.” A vowel is characterized as the product of the shape of the entire tract between the lips and larynx, without local obstruction though usually with voicing from the vocal cords. It is contrasted with a consonant, though the exact division between these two categories of speech sound is not always easy to draw. Different shaping of the tract produces the different vowel sounds of languages.
tongue position for vowel soundsDiagram showing tongue position for the vowel sounds in the English-language words heed, hid, head, had, hod, hawed, hood, and who'd.Encyclopædia Britannica, Inc.
The soft palate may be raised or lowered. It is lowered in breathing and allows air to pass in and out through the nose. In the utterance of most speech sounds it is raised, so that air passing through the mouth alone forms the sound; if it is lowered, air passes additionally or alternatively through the nose, producing nasal sounds. All but a few languages have nasal consonants (the English sounds m, n, and ng as in sing), and some, such as French, have nasalized vowels as well. A few people regularly allow air to pass through their nasal passages while they speak; such persons are said to “speak through the nose.”
All articulatory movements, including the initial expulsion of air from the lungs, may be made with greater or less vigour, giving rise to louder or softer speech or to greater loudness on one part of what is said.
Every different configuration and movement of the vocal tract creates corresponding differences in the air vibrations that comprise and transmit sound. These vibrations, like those of all noises, extend outward in all directions from the source, gradually decreasing to zero or to below the threshold of audibility. They are called sound waves, and they consist of rapid rises and falls in air pressure. The speed at which pressure rises and falls is the frequency. Speech sounds involve complex waves containing vibrations at a number of different frequencies, the most complex being those produced by the vocal cords in voiced sounds.
The eardrum responds to the different frequencies of speech, provided they retain enough energy, or amplitude (i.e., are still audible). The different speech sounds that make up the utterances of any language are the result of the different impacts on one’s ears made by the different complexes of frequencies in the waves produced by different articulatory processes. As the result of careful and detailed observation of the movements of the vocal organs in speaking, aided by various instruments to supplement the naked eye, a great deal is now known about the processes of articulation. Other instruments have provided much information about the nature of the sound waves produced by articulation. Speech sounds have been described and classified both from an articulatory viewpoint, in terms of how they are produced, and from an acoustic viewpoint, by reference to the resulting sound waves (their frequencies, amplitudes, and so forth). Articulatory descriptions are more readily understood, being couched in terms such as nasal, bilabial lip-rounded, and so on. Acoustic terminology requires a knowledge of the technicalities involved for its comprehension. Both sorts of description and classification are important, and each has its particular value for certain parts of the scientific study of language. Language acquisition
In regard to the production of speech sounds, all typical humans are physiologically alike. It has been shown repeatedly that children learn the language of those who bring them up from infancy. These are often the biological parents, but one’s first language is acquired from environment and learning, not from physiological inheritance. Adopted infants, whatever their physical characteristics and whatever the language of their biological parents, acquire the language of the adoptive parents.
Different shapes of lips, throat, and other parts of the vocal tract have an effect on voice quality; this is part of the individuality of each person’s voice referred to above. Physiological differences, including size of throat and larynx, both overall and in relation to the rest of the vocal tract, are largely responsible for the different pitch ranges characteristic of any individual’s speech. These differences do not affect one’s ability or aptitude to speak any particular language.
Speech is species-specific to humankind. Physiologically, animal communications systems are of all sorts. The animal sounds superficially most resembling speech, the imitative cries of parrots and some other birds, are produced by very different physiological means: birds have no teeth or lips but vocalize by means of the syrinx, a modification of the windpipe above the lungs. Almost all mammals and many other animal species make vocal noises and evince feelings thereby and keep in contact with each other through a rudimentary sort of communication, but those members of the animal kingdom nearest to humans genetically, the great apes, lack the anatomical apparatus necessary for speech.
The development of speech has been linked to upright posture and the freeing of the vocal cords from the frequent need to “hold one’s breath” in using the arms for locomotion. Certainly, speaking and hearing—as a primary means of communication—have a number of striking advantages: speech does not depend on daylight or on mutual visibility; it can operate in all directions over reasonably wide areas; and it can be adjusted in loudness to cope with distance. As is seen in crowded rooms, it is possible to pick out some one person’s voice despite a good deal of other noise and in the midst of other voices speaking the same language. Also, the physical energy required in speaking is extremely small in relation to the immense power wielded by speech in human life, and scarcely any other activity, such as running, walking, or tool using, interferes seriously with the process.
The characteristics just outlined pertain to all of the world’s spoken languages. What is more a matter of controversy is the extent to which biological inheritance is involved in language acquisition and language use. The fact that language traditionally has been viewed as species-specific to human beings argues an essential cerebral or mental component, and in the 19th century certain aspects of speech control and use were located in a particular part of the human brain (the Broca area, named for the 19th-century French surgeon who discovered it, Paul Broca).
Whether the great apes have the mental capacity to acquire at least a rudimentary form of language has developed into an area of active research. While apes lack the anatomical structures that are necessary for the vocalization of human speech, many investigators nevertheless claim to have taught chimpanzees, gorillas, and orangutans to communicate in languages whose “words” are composed of hand signs or geometric symbols. These claims have been disputed, with critics arguing that the apes have not demonstrated true language acquisition in the sense of understanding the “words” as symbolic abstractions that can be used in new and grammatically meaningful constructions. Researchers working with the apes, however, maintain that at least some of the apes have learned to understand and manipulate the “words” as abstractions.