Effects of Native Language and Exposure to Foreign Language on Categorization and Discrimination of Vowel Duration and Lexical Tone.

Native speakers generally outperform non-native speakers in identifying and discriminating speech sounds. Yet, the categorical perception of native speech sounds can sometimes impede the discrimination of sounds within the same phonemic category. It remains unclear whether different linguistic features show similar patterns in cross-linguistic comparisons. Therefore, we studied the categorization and discrimination of vowel duration and lexical tone-two features that differ fundamentally. Vowel duration (short vs. long) typically requires phonemic context for categorization, while tone (rising vs. falling) can be recognized directly from acoustics. Participants were native Finnish and Mandarin Chinese speakers, and native Mandarin Chinese speakers exposed to Finnish. As expected, Mandarin speakers demonstrated a steeper category boundary for tonal stimuli than Finnish speakers. In contrast, no group difference was found for categorization slope for duration. In discrimination, native speakers outperformed non-native speakers for between-category pairs, as anticipated. For within-category pairs, however, native speakers performed worse than non-native speakers-but only for the tone feature. Mandarin speakers exposed to Finnish showed differences in categorization of vowel duration and in associated reaction times compared with the other groups. The results suggest that native language does not influence vowel perception uniformly across tone and duration features. Moreover, exposure to a foreign language in adulthood may, at least initially, lead to categorization preferences that diverge from, rather than align with, those of native speakers. These findings provide a basis for future theoretical models of how native language and late exposure shape speech perception across different phonetic features.