Acoustic vowel distances within and across dialects

Regional dialects of American English exhibit variation in the phonetic realization of vowel categories. This variation leads to different degrees of phonetic vowel similarity within and across dialects. This vowel similarity has been captured by measures of formant distance and overlap in the acoustic space, typically with static formant estimates from a single timepoint in the vowel. In contrast, dialect similarity has been assessed using measures of acoustic distance over time. In the current study, dynamic measures of acoustic distance, including dynamic time warping, root mean-square distance, and generalized additive mixed effect models, were used to assess within-dialect vowel category distances and to compare these distances across dialects. The results were generally consistent across the different distance metrics, confirming their respective ability to capture acoustic vowel distance. However, the magnitude of the distances varied across dialects and vowel variables. Whereas some dialect-specific variables showed the expected patterns of within- and across-dialect similarity based on previous descriptive work, other variables did not. These mixed findings have implications for our understanding of regional dialect variation in American English, its effect on acoustic vowel similarity, and the relationship between acoustic vowel similarity and perceptual ambiguity of vowel contrasts within and across dialects.