This study examined the role of automatic selective perceptual processes in native and non-native listeners' perception of a Japanese vowel length contrast (tado vs. taado), using multiple, naturalspeech tokens of each category as stimuli in a "categorial oddball" design. Mismatch Negativity (MMN) was used to index discrimination of the temporally-cued vowel contrast by naïve adult American listeners and by a native Japanese-speaking control group in two experiments in which attention to the auditory input was manipulated: in Exp 1 (Visual-Attend), listeners silently counted deviants in a simultaneously-presented visual categorial oddball shape discrimination task; in Exp 2 (Auditory-Attend), listeners attended to the auditory input and implicitly counted target deviants. MMN results showed effects of language experience and attentional focus: MMN amplitudes were smaller for American compared to Japanese listeners in the Visual-Attend Condition and for the American listeners in the Visual compared to Auditory-Attend condition. Subtle differences in topography were also seen, specifically in that the Japanese group showed more robust responses than the American listener's at left hemisphere scalp sites that probably index activity from the superior temporal gyrus. Follow-up behavioral discrimination tests showed that Americans discriminated the contrast well above chance, but more poorly than did Japanese listeners. This pattern of electrophysiological and behavioral results supports the conclusion that early experience with phonetic contrasts of a language results in changes in neural representations in auditory cortex that allow for more robust automatic, phonetic processing of native-language speech input.

Cross-language perception studies report influences of speech style and consonantal context on perceived similarity and discrimination of non-native vowels by inexperienced and experienced listeners. Detailed acoustic comparisons of distributions of vowels produced by native speakers of North German (NG), Parisian French (PF) and New York English (AE) in citation (di)syllables and in sentences (surrounded by labial and alveolar stops) are reported here. Results of within- and cross-language discriminant analyses reveal striking dissimilarities across languages in the spectral/temporal variation of coarticulated vowels. As expected, vocalic duration was most important in differentiating NG vowels; it did not contribute to PF vowel classification. Spectrally, NG long vowels showed little coarticulatory change, but back/low short vowels were fronted/raised in alveolar context. PF vowels showed greater coarticulatory effects overall; back and front rounded vowels were fronted, low and mid-low vowels were raised in both sentence contexts. AE mid to high back vowels were extremely fronted in alveolar contexts, with little change in mid-low and low long vowels. Cross-language discriminant analyses revealed varying patterns of spectral (dis)similarity across speech styles and consonantal contexts that could, in part, account for AE listeners' perception of German and French front rounded vowels, and "similar" mid-high to mid-low vowels.

This study examined behavioral and neurophysiological indices of discrimination of an English vowel contrast [ɪ–ɛ] by early and late bilingual Spanish–English speakers, compared to monolingual English speakers. Electrophysiological measures (Mismatched Negativity – MMN) and behavioral measures (AX discrimination and forced-choice identification) were employed to examine perception of a nine-step vowel continuum, re-synthesized from natural tokens. Results revealed that (i) both monolingual and early bilinguals showed similar behavioral perception while late bilinguals performed more poorly on all behavioral tasks; and (ii) monolinguals showed robust evidence of discrimination (MMN) at a pre-attentive level that was significantly larger than found for either early or late bilinguals. These findings suggested that early input of English vowels to bilinguals did not necessarily lead to robust, automatic processing, as measured at a more attention-independent neural level; but earlier experience with a second language allowed for native-like speech perception measured with behavioral tasks.