Vowel-Tone Interaction in Two Tibeto-Burman Languages Wendy Lalhminghlui 1 , Viyazonuo Terhiija 1 , Priyankoo Sarmah 1,2 1 Department of Humanities and Social Sciences 2 Center for Linguistic Science and Technology Indian Institute of Technology Guwahati, Assam, India {wendy,viyazonuo,priyankoo}@iitg.ac.in Abstract Intrinsic F0 (IF0) has been considered a phonetic phenomenon that has a physiological basis. However, considering cross linguistic variation in IF0, it is also assumed that there is an amount of speaker intended control on IF0. This work looks into the two tone languages spoken in North East India and con- firms the evidence of IF0 in the languages. However, it also shows that as soon as speakers exert control over F0 for tone production, IF0 differences diminish. As previously reported, in this study too, IF0 differences were noticed to be more pro- nounced in the higher F0 regions. Index Terms: Intrinsic F0 (IF0), tone, Angami, Mizo, vowel tone interaction 1. Introduction In this work, we look into the interaction of tones and vowels in two Tibeto-Burman languages, namely, Angami and Mizo, spoken in the North-East of India. The specific aim of this work is to identify and account for the changes in tone characteristics due to the influence of the vowels. The positive correlation of vowel height and F0 has been referred to as intrinsic F0 (IF0) in the literature and we investigate how IF0 affects the pitch of different tones in Angami and Mizo. According to Lieberman, IF0 occurs due to a coupling ef- fect, where the shape of the vocal tract during a vowel produc- tion determines the amount of vibration of the vocal folds [1]. On the other hand, it is also argued that there is a direct relation- ship between the raising of the tongue in high vowel production and the tension on the vocal folds. According to this argument, in production of high vowels, the tongue pulls on the larynx, giving rise to high tension of the vocal folds resulting in higher F0 values [2, 3]. Ohala and Eukel provided substantial evidence for the tongue pull hypothesis through their bite block experi- ment, making it a dominant explanation for IF0 in the years to follow [4]. However, the amount of control a speaker exerts on IF0 is not quite clear. There is also an enhancement hypothesis that posits that IF0 variation is deliberate and is aimed at improving auditory salience [5]. It argues that IF0 is used as an additional feature in enhancing the perception of vowel contrasts. In other words, languages that have large vowel inventory may need IF0 to en- hance the perception of different vowel categories. While ear- lier studies did not find any correlation between vowel inventory size and IF0 differences [6], a later study confirms that there is a direct relationship between the two [7]. Contrary to that, a later work investigating IF0 differences in American English vari- eties found that the sources of the control of F0 use may not be the size of vowel inventory but may be socio-cultural, reflect- ing regional variation in speech [8]. Moreover, the same study found clear evidence of IF0 only in the vowels of prominent syllables and not so much in the non-prominent syllables. Intrinsic vowels of tone languages further complicate the situation as speakers also need to control the F0 for the best re- alization of the lexical tones. In case of tone languages, a few in- teresting observations are made in the literature [6]. While IF0 is noticed for the tone languages, the IF0 differences observed are negligible in low tones and in the lower F0 ranges. In lan- guages with more than two tone levels, the IF0 should decrease as tones become lower. For Standard Chinese, it is reported that a high tongue position, while articulating vowels, induce higher tones [9] as in non-tone languages. Clear evidence for IF0 in three African register tone languages namely, Ibibio, Kunama, Dschang; are found in a previous work [10]. The same study failed to find significant evidence of IF0 in Mambila. However, IF0 was found to be significant in Shona, a language related to Mambila [11]. While there are studies that have investigated the evidence of IF0 in Chinese and African languages, there are not many studies that have reported the interaction between vowel and IF0 in tone languages of the Tibeto-Burman family, specifically the ones spoken in India. Hence, this study aims at addressing this gap in the literature by investigating the interaction of vowel and F0 in two tone languages of the Tibeto-Burman languages family, namely, Angami and Mizo. This study tries to answer the following questions: 1. Is there any evidence of vowel effect on the F0 of tones in Angami and Mizo? 2. Do vowel effects manifest equally along the duration of the tone? 3. Considering the differences in the tone inventory of Angami and Mizo, is there a difference in the vowel ef- fect on F0 of tones? The rest of the paper is arranged in the following manner: Section 2 describes the languages and the methodology adopted in this study. Section 3 presents the results and finally Section 4 discusses the findings and concludes the study. 2. Methodology 2.1. Angami and Mizo Language Angami and Mizo are under-resourced languages of the Tibeto- Burman language family, spoken in the North-East of India. Ac- cording to the Census of India, 2011, Angami (also referred to as Tenyidie, ISO 639 - 3: njm) is spoken by 152, 796 peo- ple in Nagaland and Mizo (ISO 639-3 code: lus) is spoken by 8, 30, 846 people mainly in Mizoram and its neighbouring states of India. Both Angami and Mizo are tone languages of the Tibeto-Burman language family [12, 13]. Mizo has five vowels, Copyright  2019 ISCA INTERSPEECH 2019 September 15–19, 2019, Graz, Austria http://dx.doi.org/10.21437/Interspeech.2019-2808 3970