Iivonen & Harnud 2005, стр. 62, 66-67 Iivonen, Antti; Harnud, Huhe (2005), „Acoustical comparison of the monophthong systems in Finnish, Mongolian and Udmurt”, Journal of the International Phonetic Association, 35 (1): 59—71, doi:10.1017/S002510030500191X
Jassem, Wiktor (2003), „Polish”, Journal of the International Phonetic Association, 33 (1): 105, doi:10.1017/S0025100303001191
Hargus, Sharon; Beavert, Virginia (2002), „Predictable versus Underlying Vocalism in Yakima Sahaptin”, International Journal of American Linguistics, 68 (3): 316—340, doi:10.1086/466492
Iivonen & Harnud 2005, стр. 64, 68 Iivonen, Antti; Harnud, Huhe (2005), „Acoustical comparison of the monophthong systems in Finnish, Mongolian and Udmurt”, Journal of the International Phonetic Association, 35 (1): 59—71, doi:10.1017/S002510030500191X