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Longitudinal acquisitions of English vowels have been previously studied by Monroe (2008), Lai (2010), and others. Most of these studies rely primarily on an impressionistic methodology, i.e., native speaking judges listen to oral inputs by non-native speakers and rate the intelligibility of their vowels on a Likert scale. This is not so for this study. The assessment relies primarily on the speech signals emitted by Author 2 when reading vowels in citation form and in running speech. The F1 and F2 correlates of his vowels are measured at three different intervals: in 2011, in 2017, and in 2018. The measured correlates are compared and contrasted with each other, and with the prototypical formant values in Peterson and Barney (1952). Masking thresholds, Just Noticeable Difference (JND) limens, and relative functional load (RFL) calculations are used to determine which of Author 2’s vowels have become native-like and which ones have remained intractable over the course of seven years. The acoustic measurements from 2017 and 2018 also help investigate whether or not F1 and F2 correlates change or remain the same in citation form and running speech.



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