Vowel articulation: Tongue height and backing

An ever-present issue is tongue height and backness as a reference frame for vowel articulation. This is not new. The inadequacy of height and backness has been well known but largely disregarded for at least 85 years, since Russell (1928, The vowel, its physiological mechanism as shown by X-ray, Columbus, Ohio), and definitely for 50 years, since Fant (1960, The Acoustic Theory of Speech Production, The Hague, Mouton). This post summarizes the main milestones in phonetic theory for these two features since A. M. Bell introduced them in (1867, Visible Speech, London, Methuen:15-16,71), demonstrating their compromised status. Three of his new concepts (a continuous space between front and back, the new class of central vowels, and small increments of vowel timbre by small tongue movements in any direction) were creatively innovative. But he had no arguments, there were no new observations to build on. He knew the throat-tongue-lip model, that had existed since antiquity (Wood: 1982, X-Ray and Model Studies of Vowel Articulation, Working Papers 23, Department of Linguistics, Lund University; 1993, The throat-tongue-lip model of vowel articulation, Phonum 2:139-149, Department of Phonetics, Umeå University), and that he had used in (A. M. Bell, 1849, The Principles of Speech, Edinburgh, W. P. Kennedy), revised and reprinted several times until 1916. He also knew about the vowel tone (discovered about 200 years previously, the target of the single resonance theory, and finally identified as F2 when more resonances had been recognized). But his proposed tongue height and backness, along with constrictions located between the hard palate and the velum, were hypotheses. There was no method for observing or recording tongue positions at that time apart from peeping between the lips and probing with a straw. Negation began once vowel profiles were X-rayed and tongue positions made visible, from around 1900 onwards.

The story of these two tongue features is intimately connected with advances in the theory of speech acoustics. Bell had tied his model into the single resonance theory with height and backness determining what he called a configurative aperture suitably located along the palate in order to terminate the buccal cavity for a given vowel timbre, but he offered no explanation for how tongue height affected the timbre, nor did Sweet, and nor did Jones in any edition of (1909, The Pronunciation of English, London, Cambridge University Press) or (1918, An Outline of English Phonetics, Leipzig, Teubner; later editions Heffer). Roudet (1911, La classification des voyelles de M. Sweet, Revue de Phonétique 1:347-356) pointed out that both widening or lengthening the buccal cavity would have the same effect on its volume and resonance frequency, implying that height and backness were mutually compensating with respect to the single resonance theory. In any case, Helmholtz (1863, Die Lehre von den Tonempfindungen, Braunschweig) had already discovered two resonances for front vowels before A. M. Bell’s model was published. A. G. Bell (1879, Vowel theories, American Journal of Otolaryngology 1, July) soon confirmed two resonances for all vowels, and formulated a double resonance theory with height controlling an assumed throat resonance. Lloyd (1890-92, Speech sounds, their nature and causation, Phonetische Studien 3-5) affirmed the double resonance theory and discovered a third that he assigned to a cavity between the lips and teeth. This was the solution of the day, a unique cavity for each formant, inspired by Helmholtz’ work on resonators. For a few decades height and backness seemed to fit nicely with the double resonance theory until the 1950s, when the newly introduced spectrograph revealed numerous formants for which there were no additional cavities available. At the same time, Chiba & Kajiyama (1941, The Vowel, its Nature and Structure, Tokyo, Tokyo-Kaiseikan; reprinted 1958, Tokyo, Phonetic Society of Japan) and Fant (1960) showed the way to a more complete understanding of vocal tract resonance capable of handling every formant without recourse to height or backness.

Compromising evidence against tongue height and backness had been published by Meyer (1910, Untersuchungen über Lautbildung, in Festchrift Wilhelm Vietor, 166-248, special number of Die Neueren Sprachen) and Russell (1928), while no-one had succeeded in validating the Bell model during its 50 year existence thus far. Yet it was already hypostatized and was not to be questioned. Jones had failed to confirm his expected cardinal tongue heights by using X-ray photographs in 1917 (Collins & Mees, 1999, The Real Professor Higgins, Berlin, Mouton De Gruyter) but he continued to place his faith in tongue height and backness rather than ask why his X-rayed evidence had contradicted them. X-ray studies were giving an incomprehensibly confusing picture of vowel production to anyone whose belief in height and backness was literal rather than pragmatic. However, Wood (1982) examined 38 sets of X-rayed profiles of vowel production from 15 languages, published from 1907 to 1974, and summarized this confusion:

  • So-called central vowels did not have configurative apertures between the hard and soft palates
  • Tongue height was consistently lower for [ɪ] than for [e]
  • Only ⅓ of [ɔ] were higher than open vowels
  • Barely ⅔ of [o] were higher than open vowels
  • Only ⅓ of [u] were higher than [o]

The tongue was obviously not obeying the Bell vowel model, as Jones had seen but ignored in 1917, and Russell had seen but accepted in the 1920s. However, Wood also found that area functions for every vowel in all the same 38 sets showed without exception that only four constriction locations were being used: along the hard palate, along the soft palate (at the faucial isthmus), in the upper pharynx (at the superior pharyngeal constrictors), and in the lower pharynx (at the middle pharyngeal constrictors).

 1979figs1and2Area functions for Home Counties Southern British English vowels (left) and Cairo Arabic (right), demonstrating the four constriction locations. From the top: hard palate, soft palate, upper pharynx, lower pharynx. The English vowels are all phonemes in this accent, from the top DRESS KIT FLEECE, GOOSE FOOT, THOUGHT LOT, TRAP STRUT BATH. The Arabic vowels are all allophones of three phonemes: /i/ (hard palate), /a/ (lower pharynx), /u/ (soft palate, upper pharynx).   LP: lips. HP: hard palate. SP: soft palate. U: uvula. PHA: pharynx. LX: larynx. From Wood, 1979, A radiographic analysis of constriction locations for vowels, Journal of Phonetics 7:25−43.

Frequencies of F1 and F2 obtained by varying the degree of constriction (Amin sq cm) and the mouth opening (A/l cm) at each of the four constriction locations. The model vocal tract corresponds to a larger adult male speaker. Based on the nomograms of Stevens and House (1955, Development of a quantitative description of vowel articulation, Journal of the Acoustical Society of America 27:484-495). Examples of typical vowel timbres have been added. Adapted from Wood (1979).
©Sidney Wood and SWPhonetics, 1994-2016


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