Native non-prototypicality in vowel perception induces prominent neuromagnetic mismatch intensities in non-native speakers: a pilot study.

Neural mismatch response resulting from the difference between prediction and observation is related to change detection and discrimination. Robust neuromagnetic brain activity of auditory mismatch-related perception occurs in response to non-prototypical vowels in across-category contrasts for first-language speakers. However, whether this non-prototypicality effect applies to within-category vowel perception remains to be elucidated. Here, healthy Japanese adults (n = 7) were subjected to magnetoencephalography (MEG) while watching a silent movie, and passively listened to synthesized English vowels /i/. We observed the source-level mismatch effect to the mid-high near-front vowel deviant [ɪ] with the most non-prototypical, unspecified feature in the participants' native language system. The mismatch effect recruited the left posterior superior temporal sulcus with a peak latency of 225 ms post-stimulus onset. We further studied whether a longer F1 distance between vowel pairs would increase mismatch-activated intensities, however, we did not observe neuromagnetic changes when the prototypical anchor standard [i] was compared with three non-prototypical deviants differing in first resonance frequency (F1) values. Our results indicate that an F1 increase in within-category upper front vowel perception is a strong activator of mismatch responses measured by source-level activated intensities for non-native listeners.