Acoustic Features And Influencing Factors Of American English Diphthongs Produced By U-Tsang Tibetan Speakers

In the field of phonetic acquisition of the second language,a number of investigations on vowels have been carried out owing to their identifiable qualities.Considering the advancement of globalization and the worldwide popularity of English,studies about English vowels tend to cover subjects from many a different country and region.However,on the one hand,the number of research on monophthongs far exceeds that of examinations on diphthongs among various studies about English vowels.On the other hand,a majority of these vowel-related studies focus on learners from Indo-European language family,while those from different language families are less addressed,For example,little research has systematically reported the production of English speeches by Tibetan speakers in China along with its influencing factors.According to Speech Learning Model(SLM),it is predicted that the acquisition of American English diphthongs /a?,e?,??,??/ by Tibetan speakers is more ideal than /a?/ since there is one counterpart in Lhasa Tibetan.The current study,under the framework of SLM,recruits 20 U-Tsang Tibetan speakers with different English proficiency as subjects,and attempts to examine the acoustic characteristics of the five American English diphthongs /a?,e?,??,a?,??/ produced by native Tibetan speakers,and the contribution of such variables as gender,English proficiency and language background to possibly different performance.It is found that the gender,English proficiency and language background have different effects on the production of English diphthongs by Tibetan speakers.The major findings are listed as follows.First of all,the diphthong durations show solely significant difference in Tibetan group with different genders,with Tibetan females having longer durations than Tibetan males.And all of them have the closet duration to American English speakers for /a?/,but present the largest durational gap for /??/.Then,the onset and offset formant frequencies show the only significant difference in Tibetan groups with different English proficiency,with high-English-proficiency Tibetan students presenting a much more resemblance to American English speakers.Meanwhile,the examination of diphthong onset and offset positional properties manifests that Tibetan subjects of different genders present their own features,with the onsets and offsets of Tibetan male /e?/ and Tibetan female /??/ being closet to their corresponding monophthongs.Regarding formant movements of English diphthongs,Tibetan speakers of both genders and with different English proficiency manage to make a clear spectral distinction between the five American English diphthongs,and present identical transitional trends in producing the front closing diphthongs but exhibit variations in the back closing diphthongs.Such findings in this study confirm part of the hypotheses in SLM,that is,similar acoustic features shared by U-Tsang Tibetan and American English speakers demonstrate the creation of new phonetic inventories for American English diphthongs in Tibetan speakers.And due to the influence of language background,there is a gap in the production of American English diphthongs by native Tibetan speakers and English speakers.