John J. Ohala Department of Linguistics University of California, Berkeley 1 TAL Nanjing 2012
S tructure of the Talk • 1. Introduction: Why study physiology of tone and a brief history of discoveries. • The principal mechanism: contraction of the crico-thyroid *and adj acent muscles of larynx) • The influence of Ps (subglottal pressure) • The role of larynx height • The effect of the pharyngeal muscles (speculative) 2. Ethological determinants of speech F0 2 TAL Nanjing 2012
Why study the physiology of F0 variation? It has been demonstrated many times (by Rousselot, Passy, S ievers, Chiba & Kaj iyama, etc.) that an understanding of how speech is produced and perceived can yield explanations of sound patterns: speech sound inventories, sound changes, phonotactics, etc. This should apply to tones, tonal sound patterns, and intonation in genera., 3 TAL Nanjing 2012
Brief History of understanding of F0 variation., S peech may be considered as a sound (voice) modulated by articulations of the upper vocal tract. The latter were known from ancient times (e.g., by the S anskrit grammarians, notably Panini --, by the Arab and Persian grammarians, and the phoneticians of the Renaissance and Enlightenment, notably Amman, Wilkins, etc.) But there was some confusion and difference of opinion about what we now refer to as “ suprasegmentals” , including tone. 4 TAL Nanjing 2012
From early times voice was understood as similar to certain musical instruments, notably, wind instruments, esp. flute, horn, etc. In the mid 18th century, the idea grew that voice was generated by a strnged instrument. This was precipitated especially by the research of Ferrein 1741, hence his term: “ les cordes vocales” . This was an advance but: In fact, a musical instrument that is a closer analogue to voice is the sheng , a musical instrument used in East and S outheast Asia which uses a ‘ free reed’ , a mechanism that produces a pulse-like sound rich in harmonics over a wide frequency range. 5 TAL Nanjing 2012
The sheng : an ancient musical instrument (from East and S outheast Asia). It employs a free reed (as do some modern Western instruments such as the accordion and the harmonica). 6 TAL Nanjing 2012
I can’ t resist the impulse to inj ect parenthetically that the free reed was used in the first mechanical speech synthesizer by, Christian Gottlieb Kratzenstein, in 1781. Kratzenstein was a German physician who practiced in Russia and Denmark. He is credited with introducing the free reed in the West. 7 TAL Nanjing 2012
Now a brief review of laryngeal anatomy: My apologies: this duplicates to some extent elements in the presentation of Hiroya Fuj isaki. 8 TAL Nanjing 2012
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S ome of the most extensive and quantitative research on the action of the larynx was conducted by the pioneering German physiologist, Johannes M ü ller. The next slide shows one of his experimental set-ups. 10 TAL Nanjing 2012
11 Excised larynx TAL Nanjing 2012
M ü ller demonstrated that tilting the thyroid cartilage with respect to the cricoid cartilage was sufficient (and plausible) to account for the increase of F0 over the range found in humans. Moreover he identified the cricothyroid muscles as being located and structured in a way to accomplish this. More modern studies using EMG (incl. some by Hirano, Vennard, and Ohala) suggest that other laryngeal muscles, notably the lateral crico- arytenoid, the vocalis, and the interarytenoid are also active during F0 increases. In some cases such activity may be necessary to counteract an abductory tendency due to contraction of the cricothyroid. 12 TAL Nanjing 2012
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M ü ller quantified the effect of the weights pulling on the cartilages to stretch and thus tense the vocal cords but such quantification was difficult to translate into in vivo muscle contractions. But the results on subglottal pressure were more easily understood in real term: The result of M ü ller’ s quantification of the effect of subglottal pressure (Ps) on F0 yielded values such as 4.5 Hz/ cm H2O. 14 TAL Nanjing 2012
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This is decidedly a second-order effect and in any case it is not clear that speakers have much control over Ps in a way to purposely vary F0 . Ps is affected by glottal resistance which in turn is affected by glottal opening and vocal cord tension. 17 TAL Nanjing 2012
What M ü ller did was in vitro studies in that he used excised larynges but his results have been supported by modern in vivo studies on intact speakers. These require the skill of an otolaryngologist. I had the privilege of working with Dr., Minoru Hirano from Kurume University.. He pioneered methods of inserting electrodes into all the intrinsic and some of the extrinsic muscles of the larynx via palpation of the landmarks on the larynx and developing “ proof” criteria for verifying correct placement. 18 TAL Nanjing 2012
From this we found general patterns of laryngeal muscle activity for various functions including increasing pitch (F0). 19 TAL Nanjing 2012
This, then, is the primary mechanism for varying F0, which is the primary (though not the only) phonetic correlate of tone. But that still leaves some other aspects of the mechanism of tone to be discovered and explained. One of these is how F0 is lowered . One might think that it is simple relaxation of the muscles raising Fo that should suffice. I thought that but it turns out that isn’ t the case. 20 TAL Nanjing 2012
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From this we found general patterns of laryngeal muscle activity for various functions including increasing and decreasing pitch (F0). I don’ t fully understand this 24 TAL Nanjing 2012
Why should the sternohyoid be involved in lowering F0? Let’ s look at the anatomy; 25 TAL Nanjing 2012
The sternohyoid is not connected to the larynx but it is connected to the hyoid bone which is connected to the larynx. As it happens there is a good correlation between larynx height (in the neck) and F0. (This was known qualitatively to Greek physicians and was thought to be the principal mechanism for F0 control. It’ s not, of course, but we need to try to understand it.) 26 TAL Nanjing 2012
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This is a tracing of the larynx of a person who has paralysis of the crico-thyroid muscle. He is able to change F0 by changing the vertical position of the larynx. 31 TAL Nanjing 2012
Now, why should altering the vertical position of the larynx affect F0? The best answer I can give is that it changes the vertical tension of the vocal cords. That is, along with anterior-posterior tension of the vocal cords – controlled by the crico-thyroid, the vertical tension, controlled by the so-called strap muscles ion the neck, can also influence F0. 32 TAL Nanjing 2012
It is difficult to get direct evidence for this – at least in an intact, living, speaker, however some coronal x-rays taken by Arnold 1961 show the laryngeal ventricle increasing with increasing F0. I believe this means increasing vertical tension, too. 33 TAL Nanjing 2012
S umming up up so far: we have posited two maj or mechanisms for varying F0: contraction of the crico-thyroid and variations in larynx height. In addition we have identified one minor mechanism: changes in the transglottal air pressure. Although it is speculative, I would like to suggest that we consider a 4 th mechansim: contraction of the pharyngeal muscles. 34 TAL Nanjing 2012
It is well known that F0 is slightly different after voiced and voiceless obstruents: higher after voiceless and lower after voiced. The different is not that great: 10 ~ 15 Hz in a male speaker. But this is large enough to be detectable by a listeners. It is, moreover, the best option for the explanation of why tonal distinctions high vs. low develop after voiceless and voiced obstruents, respectively. 35 TAL Nanjing 2012
It was thought to be due to aerodynamic factors: a higher pressure drop across the vocal cords in the case of voiceless obstruent vis-à-vis voiced ones. But there is some evidence that undercuts this explanation 36 TAL Nanjing 2012
This figure show subglottal pressure for an American English voiceless aspirated stop on the left and a simple voiced stop on the right., The Ps is lower on the vowel immediately after the period of aspiration in comparison to the vowel after the voiced stop. Yet the different in F0 is has been uniformly found for American English stops. 37 TAL Nanjing 2012
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