Evidence of both brainstem and auditory cortex involvement in categorical perception for Chinese lexical tones

The categorical perception of lexical tones is important to understand tonal languages. Recent studies have provided electrophysiological evidence for the categorical perception of lexical tones at the cortical level; however, whether neural correlates exist at subcortical levels remain unknown. In this study, by using across-category and within-category lexical tone contrasts with the equivalent physical interval, we recorded deviance detection activities at both the brainstem (reflected by frequency following response) and cortical levels (reflected by mismatch negativity) simultaneously. We found that significantly enhanced intertrial phase-locking of frequency following response s was observed only during the across-category deviance detection, which indicates that phonological differences could be detected at the level of brainstem. In addition, the across-category deviants induced stronger mismatch negativity than within-category deviants. For the first time, our results demonstrate that neural correlates of categorical perception of lexical tones exist even in the brainstem, and suggests that both cortical and subcortical processes are involved in the coding and categorization of tonal information.