 According to Shipley, (a) and (y) have allophones that almost converge once they have centralized, (i) and (u) have allophones that barely centralize and drop slightly lower, approaching [ɪ] and [ʊ].Meanwhile, (e) and (o) have more change than (i) and (u) but less than (a) and (y).Vowel length is nonphonemic, and changes according to the vowel's place within the word.