1. Barry , A. S. 2007 The form, function and distribution of high rising intonation in Southern Californian and Southern British English
2. Boersma , P. Weenink , D. 2011 Praat: doing phonetics by computer (Version 5.2.19) http://www.praat.org
3. The production of new and similar vowels by adult German learners of English;Bohn;Studies in Second Language Acquisition,1992
4. Perceiving unstressed vowels in foreign-accented English;Braun;Journal of the Acoustical Society of America,2011