Investigating Variation in English Vowel-to-Vowel Coarticulation in a Longitudinal Phonetic Corpus

Understanding the nature of individual variation in speech, particularly the mechanism underlying such variability, is increasingly important, especially for research on sound change, since such investigations might help explain why sound change happens at all and, conversely, why sound change is so rarely actuated even though the phonetic pre-conditions are always present in speech. The present study contributes to the literature on inter- and intra-speaker variation in coarticulation, a major precursor to sound change, by focusing on the degree of coarticulation stressed vowels have on neighboring unstressed vowels using recordings from a longitudinal phonetic corpus of oral arguments before the Supreme Court of the United States. Significant inter-speaker variation in height coarticulation, both anticipatory and carryover, is observed, while no evidence for systematic inter-speaker variability in backness coarticulation is found. There is also no evidence for intra-speaker variation in coarticulation over the course of 205 days.