Developmental changes in Mandarin speech perception abilities in children reflected by MMN responses

Chen, Y. & Liu, H.

Department of Special Education, National Taiwan Normal University

The purpose of this study is using MMN to explore the dynamic changes of Mandarin speech perception abilities from early to middle childhood. Twenty preschoolers (Mean =3.40 yr), 18 school-age children (Mean =8.57) and 26 Mandarin-speaking adults participated in this study. Two sets of synthesized speech stimuli varying in Mandarin segmental (Consonant: alveolo-palatal affricate vs. fricative contrast) or suprasegmental features (Lexical tone: /i2/ with rising tone vs. /i3/ with contour tone) were used. The proportion of standard to deviant was 8:1, and there were 1080 trials in each condition. Six frontocentral sites (F3/Fz/F4, C3/Cz/C4) were selected for analysis. Mean amplitudes of the MMRs were calculated for seven successive 50-ms intervals, with starting point defined as 100 ms after the onset of acoustic difference between the standard and deviant in each condition. Results for consonant condition showed that the typical early MMN response only appeared in adults. Both preschool and school children showed more positive responses to the deviant during the interval of 230 to 330 ms after the stimulus onset time, while school children showed additional negative responses in the later time interval from 380 to 480 ms. For lexical tone, all children and adults showed more negative responses to the deviant stimuli, and there is a clear maturational trend from late negativity in children to early negativity in adults. The maturation of MMRs to both speech contrasts could also be observed in the change of topography, shifting from central to frontal sites and right to left in the hemisphere aspect. In sum, our results demonstrated the developmental changes in MMRs to Mandarin speech sounds. Furthermore, using contrasts representing different speech features and the specifically-defined time window based on the acoustic properties, it might provide information to clarify the possible functional roles for the different ERP components.