/i/ ranges between [i] and [e], except in unstressed syllables (as well as before consonant clusters) where it lowers to [ɪ] or [ɛ]. Similarly, /u/ lowers to [ʊ] in unstressed syllables, before consonant clusters, and word-finally. It is otherwise [u].
MacGregor, Louise A. (1995), "Kagayanen: Introduction and wordlist", in Tryon, Darrell T., Comparative Austronesian dictionary: An introduction to Austronesian studies, part 1: fascicle 1, Trends in Linguistics. 10, Berlin: Mouton de Gruyter, pp. 363–368
Olson, Kenneth S.; Mielke, Jeff (2007), "Acoustic properties of the Kagayanen vowel space", in Trouvain, Jürgen; Barry, William, Proceedinngs of the 16th International Congress of Phonetic Sciences, Universität des Saarlandes, pp. 845–848, retrieved 2009-03-15Missing |last2= in Editors list (help)
Olson, Kenneth; Mielke, Jeff; Sanicas-Daguman, Josephine; Pebley, Carol Jean; Paterson, Hugh J., III (2010), The phonetic status of the (inter)dental approximant, Journal of the International Phonetic Association40 (2): 199–215, doi:10.1017/S0025100309990296