Asymmetries in vowel perception: Effects of formant convergence and category "goodness"

The mechanisms underlying directional asymmetries in vowel perception are a focus of debate. One account – the Natural Referent Vowel (NRV) framework – suggests that asymmetries reflect a language-universal phonetic bias, such that listeners are predisposed to attend to vowels with extreme articulatory postures, which display high formant convergence. A second account – the Native Language Magnet (NLM) theory – suggests that asymmetries reflect a language-specific bias favoring “good” exemplars of native vowel categories. We examined whether listeners display asymmetries influenced by formant proximity and/or language experience. Specifically, we tested English adults in a same-different discrimination task, using /u/ vowels that systematically differed in their degree of formant proximity (between F1 and F2) and stimulus goodness. Results revealed asymmetries as predicted by NRV when vowel pairs exhibited a relatively larger difference in their F1-F2 convergence patterns, and as predicted by NLM when vowel pairs exhibited a relatively smaller difference in their F1-F2 convergence patterns.