Gradient or categorical? Towards a phonological typology of illusory vowels in Mandarin

This paper argues that illusory vowel perception, i.e., the perception of non-existent vowels between two consonants by nonnative listeners, is gradient rather than categorical in Mandarin Chinese, and that the strength of illusion is predictable from the mismatches between the nonnative speech input and the listeners’ native phonological grammar. We examined five phonological scenarios where illusory vowels with different qualities can be perceived, and different illusion levels can be predicted by factors including syllable phonotactic constraints, vowel minimality, and the place of articulation consistency between the illusory vowel and its preceding consonant. The predictions were examined in an AXB discrimination task (Experiment 1) and an identification task (Experiment 2), which confirmed the predictions overall, while some paradigmatic differences were also observed. By comparing the current results and previous reports, we argue that a gradient rather than categorical account of illusory vowel is more suitable for explaining and predicting nonnative cluster perception. Specifically, the place of articulation feature of the preceding consonant is important for predicting contextual illusory vowels, which reflects nonnative listeners’ interpretation of perceived gestural score across multiple segments, supporting a direct realist view of speech perception.