Consonants affect Tones

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 C^h < 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.

C^h = 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.

C^h > 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 C^h < 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, p^h, b, t, t^h, 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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C^h > C

Zee (1980) studied the difference between the effect if /p^h/ and /p/ on the F0 onset of the following diphthong /ei/ in Cantonese. Three male participants were asked to read the two Cantonese words (/p^hei/, /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/, /t^ha/, 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 /t^h/, 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 /t^h/ than for /t/. These differences should lead to lower onset F0 in /t^h/ 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/, /p^h/, /t/, /t^h/, /k/, /k^h/) and alveolar affricates (/ts/, /ts^h/) 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.