Where do illusory vowels come from?

Listeners of various languages tend to perceive an illusory vowel inside consonant clusters that are illegal in their native language. Here, we test whether this phenomenon arises after phoneme categorization or rather interacts with it. We assess the perception of illegal consonant clusters in native speakers of Japanese, Brazilian Portuguese, and European Portuguese, three languages that have similar phonological properties, but that differ with respect to both segmental categories and segmental transition probabilities. We manipulate the coarticulatory information present in the consonant clusters, and use a forced choice vowel labeling task (Experiment 1) and an ABX discrimination task (Experiment 2). We find that only Japanese and Brazilian Portuguese listeners show a perceptual epenthesis effect, and, furthermore, that within these participant groups the nature of the perceived epenthetic vowel varies according to the coarticulation cues. These results are consistent with models that integrate phonotactic probabilities within perceptual categorization, and are problematic for two-step models in which the repair of illegal sequences follows that of categorization.