“…Since the classic study by Peterson and Barney ͑1952͒ on the distribution of the vowel formant frequencies on the F1-F2 plane, many studies were conducted in quiet on vowel perception ͑see reviews by Strange, 1989 of difference limens for formant discrimination ͑Flanagan, 1955; Hawks, 1994;Liu and Kewley-Port, 2001͒, vowel modeling ͑e.g., Syrdal and Gopal, 1986;Molis, 2005͒, and other aspects of vowel discrimination. Many factors were found to be important for vowel identification including formant frequencies ͑Peterson and Barney, 1952͒, vowel duration ͑e.g., Ainsworth, 1972͒, F0 ͑e.g., Lehiste andMeltzer, 1973͒, spectral contrast ͑Leek et al, 1987;Poroy, 2001͒, formant contour ͑Hillenbrand andGayvert, 1993;Hillenbrand and Nearey, 1999͒, spectral shape ͑e.g., Zahorian and Jaghargi, 1986;Ito et al, 2001͒, and spectral change ͑e.g., Strange et al, 1983͒. Of these factors, the formant frequencies and spectral shape, in particular, have been found to be major cues to vowel perception.…”