From the introduction, "Earlier phonemic analysis of Magindanao (Eck, Ms) has shown that four vowels [...] can be contrasted in stressed and unstressed ante-penultimate and ultimate syllables. This paper discusses the vowel contrasts in stressed and unstressed penultimate syllables."
"Magindanao penultimate vowels,"
Work Papers of the Summer Institute of Linguistics, University of North Dakota Session: Vol. 18, Article 2.
Available at: https://commons.und.edu/sil-work-papers/vol18/iss1/2