Disentangling prominence strengthening: Evidence for independent stress and length effects in Panãra vowel acoustics

This study examines how two dimensions of phonological prominence—phonemic length and lexical stress—affect the acoustic space of vowels in Panãra, a Jê language of Brazil with one of the world’s largest vowel inventories ( Lapierre, 2023 ). We test competing predictions about prominence strengthening: the Sonority Expansion hypothesis ( de Jong et al., 1993 ), which predicts global lowering of prominent vowels, and the Hyperarticulation hypothesis ( De Jong, 1995 ), which predicts multidirectional expansion through more extreme articulation of peripheral vowels. We analyze F1–F2 data from 21 speakers, allowing us to investigate the independent and combined effects of length and stress. Panãra provides a unique test case, as stress and length operate independently, enabling clear disentanglement of their influence on the vowel space. Our results show vowel expansion for long compared to short vowels and, to a lesser extent, for stressed compared to unstressed vowels. Expansion in long vowels reflects multidirectional expansion, consistent with hyperarticulation. In stressed vowels, the expansion is driven by the lowering of low vowels, suggesting that both hyperarticulation and sonority expansion may contribute to prominence effects. These acoustic findings shed light on how different phonological mechanisms interact to shape vowel articulation, advancing our cross-linguistic understanding of prominence systems and vowel system typology. Cross-linguistic comparisons reveal consistent hyperarticulation in long vowels but more variable stress affects—patterns we link to the density of contrasts along the height dimension.