Vowel Dispersion in English Diphthongs: Evidence from Adult Production

In this paper, I address the problem of including diphthong vowels into a Dispersion Theory (Flemming 2004) framework. First, I review the main aspects of Dispersion Theory in Flemming (2004), which gives an analysis of vowel inventories using a perception-based account of contrast, but noticeably omits diphthongs, which–while different from monophthongs–are highly productive, contrastive members of vowel inventories. Next, in order to correctly represent and incorporate diphthongs, I discuss acoustic properties of diphthongs and their presence in vowel inventories cross-linguistically. Diphthongs are compared to the monophthong inventory using production data to assess their relative positions in the vowel space. The English vowel production data should reflect the language-specific constraint ranking of *Effort with the maximum contrast and minimum distance constraints as predicted in Flemming's theory. To derive diphthongs, Flemming (2004)’s constraints as well as additional constraints from Minkova & Stockwell (2003) are used to account for the distance between the two offset targets. An additional constraint is proposed to account for the strong preference in the English production data to centralize the onset targets. Derivations for individual diphthong productions compared to possible surrounding candidates are provided in the analysis.