Adjacent speech sounds are known to affect each other, which is known as coarticulation. The effect could be anticipatory (sounds affected by the following sounds) or carry-over (sounds affected by the preceding sounds) (Gandour et al., 1992). These effects have been found in several previous studies. For example, in English, vowels are generally nasalized when followed by a nasal segment (Ladefoged and Johnson, 1975). Homorganic nasal assimilation is the assimilation which assimilates a nasal consonant to the feature of place of articulation with the conditioning sound (Ohala, 1990). In other terms is that the nasal assimilated to the next consonant in place, becoming homorganic with the following consonant, such as in‧possible im‧possible.
Specific phonetic manifestation has also been found in several studies. The vowels duration, for instance, is longer when followed by voiced consonants than followed by voiceless consonants (Ladefoged and Johnson, 1975). Another example is that the voiceless stops /p, t, k/ are unaspirated after /s/ in words such as stew, skew (Ladefoged and Johnson, 1975).
In addition to the interaction between segments, segments and supra segmentals were also found to affect each other. The most well-known effect being the voicing of the prevocalic consonants affect the fundamental frequency (F0) of the following vowel.
It has been shown that F0 is lower when followed by voiced stops than followed by voiceless stops. This perturbation has been found in both tonal and in non-tonal languages (Ohde, 1984; Hombert & Ladefoged, 1977; Whalen, Abramson, Lisker, &
Mody, 1990; Lehiste and Pererson, 1961; Mohr, 1971; Fromkin, 1978).
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In the middle age of Chinese, the tones are departed because the prevocalic voicing.
This gives rise to a famous theory--tonogenesis. More description will be illustrated in the following section. The effect of voicing is well established, but the effect of aspiration less clear. The present study aims to investigate the effect of aspiration on Mandarin tones and new factors investigated are speaking rates and gender.
In the present study, how aspiration affects F0 of the following F0 is concerned.
Furthermore, the determinant of the source of the effect interests us as well.
Presumably the aerodynamic condition related to aspirated stops and unaspirated stops are different, and may result in different F0 values of the vowels. The respiratory system generates a constant subglottal pressure during closure for all stops.
At the release of an aspirated stop, high rate of airflow runs through the glottis and pressure decrease during the aspirated pronouncing (Ohala and Ohala, 1972). Isshiki (1964) noted that F0 decreased when the subglottal pressure increased. Aspirated stops thus should give rise to higher F0 of the following vowel than unaspirated stops.
Besides the aerodynamic factor of aspiration itself, Dromey and Ramig (1998) indicated that the different speaking rate resulted in different F0 performance.
Inspired by the result of Dromey and Ramig, speech rate is one of concerns in the present study.
Lai (2004) indicated that the significant rising effect of aspirated stops only was found only in female. Compared with the result of Xu and Xu (2003), there were only seven female subjects in the study and F0 was lower after aspirated stops. According to gender differences from these two opposite results, gender will be one of the factors in the present study as well.
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The aim of this paper is to provide a more consistent measurement and to help clarify the effect of consonant aspiration on the F0 of following vowels in Mandarin. Stimuli adopted in the experiment are composed of three places of articulation, four vowels, and four tones. Apart from these, Gender and Rate are also included in order to test their effect on the perturbation phenomenon. Based on the results, further discussion on our concerns will be addressed.
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Chapter II Literature Review
2.1 Segmental interaction 2.1.1 Consonants affect vowels
Speech segments are known to affect each other. The interaction between consonants and vowels has been investigated widely. Many papers have reported the segmental interaction between consonants and vowels (Peterson & Lehiste, 1960; House, 1961;
Umeda, 1975). Peterson & Lehiste, (1960) pointed out that all syllable nuclei in English are significantly affected by the nature of the consonants that follow the syllable nuclei. For example, the syllable nucleus is shorter when it is followed by a voiceless consonant, and longer when followed by a voiced consonant.
Another statement where consonants affect vowels is during vowel nasalization.
Vowels tend to become nasalized before nasal consonants (VN ) (Ladefoged and Johnson, 1975). The nasalized vowels are produced primarily by lowering the velum, resulting in opening a side passage for air flow through the nasal cavity. In addition, the cross-language phonological evidence indicates that vowels are more likely to be affected by nasal assimilation when followed by a syllable-final nasal consonant than when preceded by a nasal consonant (Krakow, 1999; Clumeck, 1976).
2.1.2 Consonants affect Tones Voicing and F0
In addition to the interaction between segments, segment and supra segmental were also found to affect each other. The effect of the prevocalic consonants, particularly voicing, on F0 of the following vowel has been discussed in many studies. It is well-known that F0 is higher when followed by voiceless stops than by voiced stops.
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Previous studies show a common consensus when the F0 of following vowels is lower after voiced consonants in both tonal and non-tonal languages (tonal: Matisoff (1971), Gandour, (1975); nontonal: Ohde (1984), Hombert & Ladefoged (1977), Whalen, Abramson, Lisker, & Mody (1990), Lehiste and Pererson (1961) Mohr (1971), Fromkin (1978)).
House and Fairbanks (1953) investigated the variation of vowels varying in different consonantal environments in English. The general plan was to place vowels in various consonant environments (CV syllables which C=/p, t, k, f, s, b, d, g, v, z, m, n/ and V=/i, e, a, o, æ , u/). The CV syllables were produced by 10 male subjects. The duration and F0 of vowel were measured. The duration measurement showed that the vowel duration was longer in the voiced environments. Furthermore, results revealed that F0 was higher after voiceless stops than after voiced stops.
Fromkin (1978) conducted a similar experiment on how voicing affects F0 in American English. Five subjects are asked to produce six CV nonsense word (C = /p, t, k, b, d, g/, and V = /i/) in the frame ―Say __ again‖. With reference point at the onset of the vowel, F0 was measured at onset and at 20, 40, 60, 80, and 100 ms after the onset. The result showed that F0 of vowels after the voiced stops is lower than after voiceless stops. Fromkin explained the phenomenon in the following terms. ―After the closure of voiced consonant, voicing continues, but since the oral pressure increases, the pressure drop decreases, leading to a lower frequency. The F0 then rises after the release until it reaches the ‗normal‘ value of the vowel which is being realized.‖
In addition to make the different performance on duration and F0, voicing also causes another phonetic phenomenon in Mandarin—tonal split. During middle age of
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Chinese, people found that the tone is lower when producing voiced stops, and the tone is higher when producing voiceless stops. Thus, the tone is departed after voiced obstruents, and the differential way in which voiced stop and affricates devoiced in Mandarin. For instance, each of the Middle Chinese tonal categories splits to high and low registers—known as ying and yang in Chinese phonology—yielding a perfectly symmetrical eight-tone system. In each case, the yang register with a voiced onset has a lower pitch values than the corresponding yin register with higher pitch values (Chen, 2000).This gives rise to a theory—tonogenesis—in which development of contrastive tones are due to the loss of voicing distinction in prevocalic obstruents (Pulleyblank, 1986).
The rising effect of voiceless stops may be explained by physiological mechanisms—the vocal folds tension. In making the voiced vs. voiceless distinction on stops, vocal folds tension is changed so as to affect the F0 of adjacent vowels (Hombert et al., 1979; Fromkin, 1978). Halle and Steven (1971) suggested that these intrinsic variations are the result of horizontal vocal folds tension: the vocal folds are presumably slack in order to facilitate voicing during voiced stops and stiff in order to inhibit voicing during voiceless stops. These vocal folds states spread to adjacent vowels, affecting their F0. Another variant of the vocal folds tension hypothesis is that which suggests that it is the vertical tension of vocal folds which is affected by the voiced vs. voiceless distinction (Ohala, 1973, Ewan 1979, Steven 1975).
Furthermore, the aerodynamic hypothesis may explain the rising effect of voiceless stops. When producing a voiced stop, oral pressure gradually builds up, this decreases the pressure drop across the vocal cords—which in turn decreases the F0. Upon the release of the stop, the pressure drop returns to normal, producing an initially low and
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rising F0 contour after voiced stops (Ladefoge, 1967). In the case of voiceless stops, the airflow past the vocal cords is very high upon release, creating a high-than-normal Bernoulli force—which will draw the vocal cords together more rapidly, and so increase the rate of their vibration at vowel onset. As the airflow returns to normal, the F0 will too. Thus, after voiceless stops, the F0 contour will be initially high and falling (Ohala, 1970; Ohala and Ewan, 1973; Abramson 1974; Hombert and Ladefoged, 1977).
Aspiration and F0
Although the effect of voicing on F0 is widely regarded, research about the effect of aspiration on F0 has received less scholarly attention. The possible effect of aspiration on F0 is particularly interesting when it induces possible phonetic contrast. A series of documentations regarding aspirations as a cause of tone splitting have been published.
Tonal split caused by prevocalic aspiration was documented in some Chinese languages, such as Wu, Gan, Xiang, and Miao (Ho, 1990; Shi, 1998). Although no instrumental research was conducted, both Ho and Shi argued that F0 is lower after aspirated stops due to the lowering of the larynx when producing aspirated stops.
There is no conducting regarding the effect of aspiration on F0. Three kinds of results regarding this perturbation effect have been provided. One is that F0 is lower after aspirated stops, data was found in Korean (Kagaya, 1974), Cantonese (Francis et al., 2006) and Mandarin (Xu & Xu, 2003). Another is that there is no difference in F0 after aspirated or unaspirated stops, for instance, Hombert and Ladfoged (1977).
Finally, F0 is higher after aspirated stops. Examples can be found in Cantonese (Zee, 1980), Korean (Kenstowicz & Park, 2006), and Taiwanese (Lai, 2004).
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Form above, there exists no agreement and different results within the same languages were found (in Korean Kenstowicz & Park (2006) vs. Kagaya (1974)). Related researches conducted on non-tonal and tonal languages will be reviewed respectively in the following section; in addition to studies on aspiration and F0 in Mandarin as well.
Non-tonal languages Ch < C
In non-tonal languages, Kagaya (1974) studied the laryngeal gestures of three types of consonants in Korean. Two native speakers of Seoul dialect were recorded producing /CV/ and /VCV/ in isolation. F0 was measured for each sample, by averaging values for the first three fundamental periods from voice onset. The results showed that F0 at voice onset of the aspirated type is lower than ones of the unaspirated stops.
Ch = C
Hombert and Ladefoged (1977) investigated the two series of voiceless stops in English and French (the English series is voiceless aspirated as opposed to the French series which is supposed to be voiceless unaspirated). Two American English speakers (1male, 1female) and 2 French speakers (1male, 1female) were asked to produce 6 CV nonsense words (consonants = /p, t, k, b, d, g/ and vowel = /i/) in the frame—―Say ___ louder‖. Results indicated that these two series of voiceless consonants (English voiceless aspirated stops and French voiceless unaspirated stops) had very similar effect on the F0 contours of the following vowels.
Ch > C
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Kenstowicz and Park (2006) investigated the three-way contrasts in Korean Kyungsang dialect and how F0 was utilized to implement the tonal and laryngeal contrast in Kyungsang. Seven speakers (2 males, 5 females) were recorded producing 48 words in a sentential frame. A number of measurements were taken including VOT and F0 at four points (the onset, the mid-point of the first and of the second vowels).
Results showed that VOT of aspirated stops was the longest and that F0 of vowels following tense and aspirated consonants have higher F0 than those following a lax consonant. The data indicated that the laryngeal category of the onset consonant has a systematic effect on the F0 value of the following vowel that is highly significant at both the onset and middle of the vowel.
There is no consistent agreement in the non-tonal languages form above investigations. The few studies on non-tonal languages suggest that aspiration has both rising effect (Kenstowicz & Park, 2006) and lowering effect (Kagaya, 1974), or the similar effect on aspiration (Hombert & Ladefoged, 1977).
Tonal Languages Ch < C
Tonal languages such as Thai (Gandour, 1974), and Cantonese (Zee, 1980; Francis, 2006), for many years have been investigated to uncover the relationship between aspiration and the following vowel for many years. Gandour (1974) investigated the effect of preceding consonants on tone in Thai. A male speaker was asked producing CV1V2 syllable where C=/p, ph, b, t, th, d, s, n/, V1=V2= /a, i, u/ with five tones and F0 was measured. Gandour found that the initial F0 value after the release of an unaspirated stop is higher for a voiceless aspirated stop.
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Ch > C
Zee (1980) studied the difference between the effect if /ph/ and /p/ on the F0 onset of the following diphthong /ei/ in Cantonese. Three male participants were asked to read the two Cantonese words (/phei/, /pei/) in a sentence frame at a normal rate of speech.
A F0 measurement for each test word was obtained every 10ms. The result showed that for all the tokens the F0 onsets associated with aspirated stops were higher than those associated with unaspirated for all three speakers.
Francis et al. (2006) investigated the effect of aspiration differences in Cantonese initial stops on the F0 of the following vowels, as well as the interaction of this effect with tone contour. 16 native speakers of Cantonese (8 males, 8 females) were asked to producing CV syllables with six tones. F0 of vowels after aspirated and unaspirated was measured over the first 100 ms. Results showed that the onset F0 is higher after unaspirated stops than after aspirated ones. In addition, there is a falling F0 contour over the first 100 ms, consistent with the voiceless status of both aspirated and unaspirated stops.
Mandarin
Tonal splits are triggered by aspiration in some Chinese dialects such as Wu and Tanyang (Chao, 1967). Chao (1967) pointed out that the most characteristic feature of Wu dialects is the tripartite division of initial stops into voiceless unaspirated, voiceless aspirated and voiced aspirated. However, not only Chao mentioned the phenomenon of tonal splitting by aspiration, Shi (2007) remarked as well on it in the northern Wu dialect. Shi (2007) indicated that the characteristic of Wu dialect is that aspirated tones are realized as lower register tones.
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Besides the voicing parameter, aspiration is another important aspect in differentiating the relationship between F0 and the prevocalic consonants. More investigations were conducted by Xu and Xu (2003) for Mandarin. Xu and Xu (2003) investigated the effect of consonant aspiration on the following vowels. Seven females native speaker were asked to read the stimuli (/ma/, /ta/, /tha/, and /ʂa/ with four tones) in two carrier sentences—wo3 lai2 shuo1 ____ zhe4 ge4 ci2 (‗I say the word ____‘) and wo3 lai2 zhao3____ zhe4 ge4 ci2 (‗I look for the word ____‘). F0 of these targets words were
measured by an automatic vocal detection and manual rectification. The results indicated that the onset F0 is higher following unaspirated consonants than following aspirated consonants. Xu and Xu (2003) indicated that during the closure of the stops, pressure builds up to a constant level irrespective to the aspiration feature of the consonants. At the release of /th/, pressure decreases markedly and at the release of /t/, however, pressure remains at a high level and gradually returns to normal. Pressure should be lower at the voice onset for /th/ than for /t/. These differences should lead to lower onset F0 in /th/ than in /t/.
In addition, Lai (2004) studied whether and how aspiration influences the tones in Taiwanese. Four participants (2 males, and 2 females) were asked to produce 56 CV(O) syllables, consisting of the stops (/p/, /ph/, /t/, /th/, /k/, /kh/) and alveolar affricates (/ts/, /tsh/) followed by a vowel (/i/, /ɛ/, /a/, /u/, and /o/) with seven tones.
VOT, and F0 (onset F0, end of F0, and mean F0) were measured. Results showed that onset F0 and mean F0 are significantly higher after aspiration stops than after unaspirated ones. F0 after aspirated stops is higher than after voiceless unaspirated stops due to the faster airflow rate and higher larynx position. Further analysis in Lai (2004) showed that this rising effect was only significant in females and not in males.
Compared with Lai (2004) and Xu and Xu (2003), the aspiration rising effect is
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opposite in their result. Inspired by the gender difference, the present study recruited more subjects and greater efforts were made to balance the gender of the participants.
The results of tonal languages are similar to that of non-tonal languages. No agreement can be reached with respect to the effect of the aspirated stops on F0. The disagreement certainly requires further research on this aspect.
2.2 Determinants of F0
Next, the interaction between segment and F0 is investigated, the physiological factor which affects F0 are reviewed in this section. Two aspects of laryngeal mechanisms are discussed here: the internal factors are defined as the coordination of muscles in the larynx; on the other hand, the height of the larynx is defined as external factor (Hirano and Ohala, 1969). Moreover, the aerodynamic and speaking rate will be reviewed as well.
2.2.1 Physiological Factors of F0 control The anatomy of larynx
A basic function of the larynx and the mechanics of voice production are necessary to be understood before discussing the production of F0 can be discussed. The larynx plays the role of breathing, speaking and swallowing in the human body. The epiglottis is closed to ensure that food will pass through the pharyngeal cavity into the esophagus. In speech, the larynx is important as an articulator and a source of sound.
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Figure 1. Anterior view of larynx
(adopted from http://en.wikipedia.org/wiki/File:Larynx_external_en.svg)
The larynx (Fig. 1) has a skeletal frame formed by a series of cartilages. There are two main cartilages—the upper thyroid cartilage and the lower and smaller cricoids cartilage. The epiglottis lies superiorly; it protects the larynx during swallowing and prevents the inspiration of food.
The most prominent laryngeal cartilage is called the thyroid cartilage. It consists of two plates which are arranged in a wedge-like shape. The hyoid bone is found above the thyroid cartilage. It is connected to the larynx by the thyrohoid membrane. The U-shaped hyoid bone serves as an attachment point for the tongue muscles. Beneath the thyroid cartilage is the cricoids cartilage, which forms the base of the larynx. The anterior part of the cricoids cartilage is narrow and referred to as the arch. The
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posterior part, which is called lamina, is much broader and forms much of the larynx‘s back wall. The cricoids cartilage supports the thyroid cartilage and the arytenoids (see Fig. 2). Its upper edge from four articulatory surfaces: two at the side for the thyroid and two at the back for the arytenoids. Above to the lamina are the arytenoids cartilages, which attach to the vocal folds. A pair of triangle-shaped arytenoids cartilages is located along the upper edge of cricoids lamina. On the top of each arytenoid cartilage is a small corniculate cartilage. Each arytenoid cartilage attaches itself to the posterior end of a vocal ligament (Marchal, 2009).
Figure 2. The larynx seen from the back and right side (adopted from Lai (2009))
Vocal Folds
F0 control is at the larynx is considered to be achieved by the adjusting the effective and the stiffness of the vocal folds (Hirose, 1997). The studies of vocal folds have been investigated for many years (Hirano, 1981; Hirano, 1983), with the objective of
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understanding the behavior of the folds during speech. The vocal folds are twin infoldings of membranes and muscular fibers stretched horizontally across the larynx.
They are located below the epiglottis. They are attached at the back to the processes of the arytenoids cartilage and at the front to the thyroid cartilage. Above the vocal
They are located below the epiglottis. They are attached at the back to the processes of the arytenoids cartilage and at the front to the thyroid cartilage. Above the vocal