关键词: 语音范畴知觉，声调，顶下叶，fNIRS，TMS

Abstract: The left Inferior Parietal Lobe (IPL) is a critical brain region for speech category perception, and some studies have found that this region is involved in the categorical perception of Chinese tones. However, its specific role in the perception of tones is unclear. The current study manipulated both the tonal categories (inter-category vs. intra-category) and acoustic features (large vs. small acoustic intervals) of successively presented stimulus pairs to examine whether the IPL is sensitive to acoustic features or abstract representation of tonal categories in the perception of Chinese tones. Experiment 1 used functional near-infrared spectroscopy (fNIRS) techniques to localize the functional activation of IPL in tonal perception. Experiment 2 used the transcranial magnetic stimulation (TMS) technique to virtually impair the IPL and establish the neural causal link between the IPL and tonal categorical perception. Experiment 1 revealed that the dorsal channel of IPL was sensitive to tonal categories, showing more robust IPL activation induced by inter-category than intra-category stimulation, and it was also sensitive to acoustic intervals, showing stronger IPL activation induced by small acoustic intervals than large acoustic intervals stimulation. Experiment 2 virtually damaged the dorsal and ventral IPL channels separately. When TMS inhibited the dorsa IPL channel, the sensitivity of this channel to tone categories disappeared. In contrast, the ventral IPL channel and the left premotor cortex (PMC) channel were sensitive to acoustic intervals, showing stronger IPL activation induced by large than small acoustic intervals. However, when TMS inhibited the ventral IPL channel, only functional compensation in the left inferior frontal gyrus channels showed activation of sensitivity to tonal categories induced by within than between category stimulus pairs. In sum, this study displayed an important role of the left dorsal IPL in Chinese tonal categorical processing. In contrast, the ventral part of the IPL plays an essential gating role in the dorsal pathway of tonal categorical perception. The research results have enriched the neurophysiological model of speech perception from the perspective of tonal language, elucidating the collaborative mechanism between dorsal and ventral speech streams in categorical perception.

Key words: Speech category, Tone, inferior parietal lobule, fNIRS, TMS