To assess the extent to which acoustic and phonetic change-detection processes contribute to the mismatch negativity (MMN) to linguistic pitch contours.
MMN was elicited from Mandarin and English speakers using a passive oddball paradigm. Two oddball conditions were constructed. In one condition (T1/T2i), the Mandarin high-level tone (T1) was compared with a convex high-rising tone (inverted T2, henceforth referred to as T2i) that occurs as a contextual variant of T1 in running speech. In the other (T2/T2i), the concave high-rising tone (T2) was compared with T2i. Phonetically, T1/T2i represents a within-category contrast for native speakers, whereas T2/T2i represents a between-category contrast. The between-category pair (T2/T2i), however, is more similar acoustically than the within-category pair (T1/T2i). In an attention-demanding behavioral paradigm, the same speakers also performed an auditory discrimination task to determine the perceptual distinctiveness of the two tonal pairs.
Results revealed that the Chinese group, relative to the English, showed larger MMN responses and earlier peak latencies for both conditions, indicating experience-dependent enhancement in representing linguistically relevant pitch contours. At attentive stages of processing, however, the Chinese group was less accurate than the English in discriminating the within-category contrast (T1–T2i).
These findings demonstrate that experience-dependent neural effects at early preattentive stages of processing may be driven primarily by acoustic features of pitch contours that occur in natural speech. At attentive stages of processing, perception is strongly influenced by tonal categories and their relations to one another. The MMN is a useful index for examining long-term plasticity to linguistically relevant acoustic features.