Truncation of pharyngeal gesture in English diphthong [aɪ]

It is well acknowledged that [a] in English diphthongs (e.g. [a] in “pie’d”) has a different formant structure from its closest corresponding monophthong (e.g. [a] in “pod”). The current study proposes that these two sounds share the same cognitive unit, i.e. the pharyngeal constriction gesture that produces [a], and the surface difference can be modeled as a consequence of truncating the same articulatory movement in time by the following palatal glide in the diphthongal environment. Formation of pharyngeal constriction gesture during the production of [a] in a diphthong and in its corresponding monophthong was observed in various timing contexts using Realtime MRI; and the collected production data were quantitatively analyzed using the direct image analysis (DIA) technique, which infers tissue movement by tracking pixel intensity change over time in regions of interest. Results support our truncation account in that: (1) formation time of pharyngeal constriction is significantly longer in monophthongs than in diphthongs; (2) this duration correlates with the resulting constriction degree; and (3) the resulting constriction degree predicts the acoustic difference in the F2 dimension as predicted by our hypothesis.