包含普通话母语者在内，全球有接近70%的人口在使用声调语言。言语声调，作为声调语言中的超音位音素，决定着每个字的含义。然而，过往的研究将目光更多地集中在声母、韵母等音素，较少有对声调知觉的研究。近期的研究显示，声调语言母语儿童声调知觉能力能预测其未来阅读能力的发展，提示声调知觉的发展在儿童语言能力发展过程中扮演着重要角色 (Shu et al., 2008)。然而，关于声调知觉能力的发展以及其神经机制的研究目前仍十分缺乏。对这一领域的研究可以帮助我们了解语言的学习过程（尤其是声调语言）。此外，音高作为音乐中必不可少的构成元素，同时也是辨别言语声调的重要听觉线索。已有研究显示，成人普通话母语音乐家的普通话声调辨别能力要明显优于成人非音乐家，而一部分具有音乐音高加工缺陷的失乐症者也表现出了明显的普通话声调加工的问题。这些研究成果都提示音乐音高加工能力可能与普通话声调知觉的发展紧密相关。研究二者的关系将为通过音乐干预语言障碍尤其是声调障碍提供关键实证依据。同时，从理论角度出发，音乐与语言的关系以及二者的进化根源一直是科研界所关注的重要问题。研究音乐音高与言语声调的关系可以帮助我们了解音乐与语言领域中的音高加工过程存在怎样的重合与分离，进而以还原论的思想来探讨音乐与语言的关系。在本项目中，我们通过四个研究，研究言语声调知觉能力的发展以及音乐音高加工能力的影响。

　　对普通话母语者来说，普通话声调知觉能力的获得似乎是件自然而然的事情。但实际上，言语声调知觉能力可能要到10岁左右才接近成熟 (Ciocca & Lui, 2003)。而且，过往的研究大多单独研究声调或音高加工能力，很少将二者结合在一起研究，以了解二者发展的关系。此外，声调的重要性在近年虽有研究提及但并没有得到充分的强调 (Hong et al., 2018; Shu et al., 2008)，目前更少有研究者关注声调知觉对儿童语言能力发展的影响。因此，在研究一中，我们首先想要了解普通话母语儿童的声调知觉发展特征，以及音乐音高加工能力发展与言语声调知觉发展的关系，并进一步探究言语声调知觉对学龄儿童语言能力发展的重要意义。通过比较学龄儿童（9岁）与成年人声调语言母语者的普通话声调以及音乐音高辨别能力，我们发现即便是9岁的普通话母语儿童，其普通话声调辨别能力依然远远没有达到成年人水平。这种发展中状态不仅表现在行为成绩上，也同样表现在不成熟的神经反应上（脑电上波幅小于成人的P3a和明显的LDN（晚期识别负波，late discriminative negativity）成分，以及更不稳定的神经反应（试次间一致性，inter-trial coherence, ITC）。同时，儿童的音乐音高加工也表现出相似的未成熟发展状态，并与言语声调知觉能力高度相关。随后我们又重复测量了儿童两年后（11岁）的各项行为成绩，发现虽然普通话声调和音高辨别能力均有提高，但依然显著低于成年人，表明普通话声调知觉发展即便在完成了拼音学习后数年也没有完全成熟。此外，音乐音高辨别虽然在9岁儿童中与言语声调辨别高度相关，但其辨别能力却明显差于言语声调辨别，暗示言语声调的辨别能力发展要快于音乐音高加工。最后，相关分析发现，9岁儿童言语声调辨别成绩可以预测其11岁时的识字量。这一结果说明，言语声调的发展可能与阅读能力的发展相关。总的来说，研究一揭示了儿童在小学高年级言语声调依然未能发展成熟的发展特点，同时发现言语声调发展与阅读能力发展的相关关系。音乐音高测试的加入，让我们了解到音乐音高辨别能力确实与言语声调辨别存在着高度相关，但二者发展的过程并不完全同步。

　　基于研究一所发现的学龄儿童的言语声调知觉依然处于发展阶段的特点，我们在研究二中进一步探究，音乐经验如何影响学龄儿童的普通话声调知觉的发展。通过行为测试结合脑电的实验方法，我们比较了具有一定音乐训练经验的音乐家儿童与非音乐家儿童（9岁）的言语声调和音乐音高辨别能力及脑电反应。结果显示，音乐家儿童不仅表现出比非音乐家儿童更强的音乐音高辨别能力，他们对言语声调的辨别能力也明显优于非音乐家儿童。同时，音乐家对两种刺激的脑电反应也与非音乐家差异明显，表现出更趋于成熟的脑电成分特征（更高的P3a平均波幅，更小的LDN平均波幅），提示音乐训练可能促进言语声调加工的发展。此外，音乐家对言语声调的脑电反应，仅在左侧半球强于非音乐家。这种偏侧化现象可能说明：音乐训练不仅能增强声调语言母语者对言语声调的神经反应，还可能促进其对声调的特异性加工网络的发展成熟。

　　优秀的音高加工能力与更好的言语声调知觉有关。那么如果音高加工能力发展异常，将会如何影响声调语言母语者的言语声调加工？在研究三中，我们考察了普通话母语失乐症（一种以音乐音高加工困难为主的音乐发展障碍）的音乐音高加工以及普通话声调加工。研究采用了与研究一、二相同的实验范式，测量了失乐症和控制组的音乐音高与言语声调辨别能力，并记录了所有被试对两种刺激变化的脑电反应。结果显示失乐症对音乐音高与言语声调的辨别能力要明显弱于控制组，表明失乐症的音乐音高加工异常可能也影响到了言语声调知觉。脑电结果显示，音高与言语声调刺激诱发的P3a波幅在失乐症组中均低于控制组，提示失乐症的异常可能与对听觉音高信息的脑神经反应减弱有关。有趣的是，时频分析结果显示，失乐症仅表现出对音乐音高的脑电反应稳定性下降（试次间一致性），而对言语声调的脑电反应稳定性与控制组没有差异。同时，行为水平失乐症的声调加工成绩也明显高于其音乐音高加工成绩。这一发现表明失乐症者的普通话声调加工虽然受到了音乐音高发展缺陷的影响，但可能依然发展出了相对稳定的神经网络，保留了一定程度的对言语声调的辨别能力。

　　最后，在探究言语声调知觉发展特点的基础上，我们尝试进一步从脑白质神经纤维连接的角度出发，研究言语声调知觉发展的脑机制，并分析音乐音高加工能力变化对言语声调加工的影响在脑结构方面的表现。在研究四中，我们聚焦于双侧弓形束结构。弓形束作为连接语音加工背侧通路的重要神经连接 (Hickok & Poeppel, 2007)，连接负责音高加工的两个重要脑区，前额叶与颞叶  (Nan & Friederici, 2013; Peretz, 2016)，与语音加工关系密切  (Su, Zhao, et al., 2018)，其发育过程贯穿青少年期 (Paus et al., 1999) 。因此，对弓形束的研究可以揭示言语声调知觉发展的关键脑机制。研究四使用弥散张量成像，分析了声调语言母语失乐症者与控制组的弓形束连接性差异及其与语言声调加工的关系，探究言语声调知觉发展的神经机制以及音乐音高加工异常对言语声调加工造成影响的神经基础。结果显示，失乐症的右侧弓形束额顶连接的体积明显低于控制组，而右侧顶颞连接的部分各向异性指数明显高于控制组。该结果提示失乐症音高加工异常可能与右侧额-顶-颞网络连接异常有关。并且，失乐症者的左侧弓形束额颞连接各向异性指数与其声调测试成绩表现出明显的负相关，但是并没有出现明显的组间差异，这说明失乐症的言语声调加工缺陷与左侧背侧通路连接性变化有关。失乐症组与控制组主要差异出现在右侧，与音乐的音高加工障碍有关，但其左侧与语言声调加工有关的连接异常并未达到显著。这一发现与实验三的结果一致，表明音乐发展障碍对语言声调发展的影响可能是有限的，语言声调发展与音乐音高发展的轨迹并非完全重合。研究四的结果提示声调语言母语者的左侧弓形束可能与言语声调知觉有关，且音乐音高加工能力与言语声调知觉的联系也可能在一定程度上以弓形束为基础。

　　总之，本项目通过四个研究，探索了普通话声调知觉发展的特征；并从音乐经验与音乐发展障碍两方面，分析了音高加工能力对普通话声调知觉发展的影响；最后通过结构成像来探索言语声调知觉发展的神经机制，以及音乐音高影响言语声调发展的神经基础。我们的研究发现：普通话声调的发展与阅读能力的发展高度相关，但普通话声调本身的发展在小学高年级（9-11岁）依然没有成熟。对9岁的学龄儿童来说，具有音乐经验的儿童，其言语声调辨别以及对言语声调变化的脑电反应都要强于非音乐家儿童。而对于失乐症者来说，其音高加工的异常波及到了言语声调加工，表现出了对声调辨别的成绩低下且对言语声调变化的脑电反应异常。最后，失乐症的异常表现在背侧通路上弓形束连接的连接性异常，其左侧弓形束的连接性强度与失乐症的言语声调加工异常相关。基于以上的研究成果，未来的研究者可以围绕三个问题进行后续研究：（1）声调语言母语者言语声调知觉的发展轨迹。（2）音乐音高加工能力在言语声调发展不同阶段对其的影响。（3）言语声调发展的神经基础以及其与音乐音高加工的神经网络的关系。同时，后续还可以采用纵向追踪的方法来对本项目现有的结果进行验证和补充。

Nearly 70% of the world's population, including native Mandarin speakers, speaks tonal languages. Lexical tones, as suprasegmental features in tonal language, determine the meaning of each word. However, previous studies have paid more attention to phonemes such as consonant and vowel than lexical tone perception. Recent studies have shown that lexical tone perception of tonal language-speaking children could predict their reading development, suggesting that the development of lexical tone perception plays an important role in the development of children's language ability (Shu et al., 2008). However, the research on the development of lexical tone perception and the underlying neural mechanism is now still lacking. Research in this area can help us understand the process of language learning (especially for tonal language). In addition, pitch is not only an indispensable element in music but also an important auditory cue for lexical tone discrimination. Previous studies demonstrated that the musician adults speaking Mandarin discriminate lexical tones better than nonmusicians, and a small minority of congenital amusics who have deficits in musical pitch processing also meet problems with Mandarin tone discrimination. Therefore, musical pitch processing may be closely related to the lexical tone perception development. The revealing of the relationship between musical pitch and lexical tone processing will provide experimental evidences for intervention of people with deficits in lexical tone perception using music therapy. Theoretically speaking, the relationship between music and speech, and the evolutionary roots of them keep attracting researchers’ attentions. Studying the relationship between music pitch and speech tone can help us understand the associations and dissociations between pitch processing in music and which in speech, and then help exploring the relationship between music and speech based on reductional theory. In this project, through four researches, we investigated the development of lexical tone perception and the influence of musical pitch processing.

For native Mandarin speakers, the acquisition of lexical tone perception is a process without difficulty. However, even in native tone language speakers, their perception of lexical tone seems not mature until 10 years old (Ciocca & Lui, 2003). Moreover, most of the previous studies focused on either lexical tone or musical pitch, but rarely investigate them together, so that to understand the relationship between the development of the musical pitch and lexical tone processing. In addition, few researchers pay attention to the influence of tone perception on children's language development. Although the importance of lexical tone has been mentioned in recent years, it has not been fully emphasized (Hong et al., 2018; Shu et al., 2008). Therefore, in Study 1, we firstly tried to understand the developmental characteristics of lexical tone perception in Mandarin-speaking children, and the relationship between the development of musical pitch processing and the development of lexical tone perception. Meanwhile, we further explore the importance of lexical tone development for the development of language ability in school-age children. By comparing the lexical tone and musical pitch discrimination in school-age children (9 years old) with adults, we find that even for 9-year-old Mandarin-speaking children, their lexical tone discrimination is still far below the adult’s level. This developing state is not only reflected by behavioral performances, but also by immature neural responses (weaker P3a compared with adults, easily observed LDN components, and less stable neural responses reflected by inter-trial coherence). Meanwhile, children's musical pitch processing also exhibits a similar development state and is closely related to lexical tone perception. We then repeatedly measured the children's behavioral performances two years later (11 years old), and found that although both of lexical tone and musical pitch discrimination improved, they were still lower than adults. This result proved that the development of lexical tone perception is not fully matured even after several years since they finished the study of Pinyin. In addition, although musical pitch discrimination is correlated with lexical tone discrimination in 9-year-old children, children’s musical pitch discrimination is significantly worse than lexical tone discrimination, suggesting that the development of lexical tone discrimination might be faster than musical pitch discrimination. Finally, correlation analysis found that the lexical tone discrimination of 9-year-old children is correlated with their literacy outcomes at the age of 11. This result suggested that the development of lexical tones is related to the development of reading ability. In general, the first research proved the importance of lexical tone development for the development of reading ability, and also revealed lexical tone perception is still immature in the senior grade of elementary school. The musical pitch test revealed that the musical pitch discrimination ability is closely related to lexical tone discrimination, but their development trajectories might be not completely synchronized.

The findings of study 1 suggested that lexical tone perception in school-age children is still in the development stage. Based on this, in the second study, we further explored how music experience affects the development of lexical tone perception in school-age children. Using behavioral tests combined with EEG experimental methods, we compared musician children’s lexical tone and musical pitch discrimination with nonmusician children at both behavioral and neural level. The results show that musician children show not only stronger musical pitch discrimination than non-musician children, but also better lexical tone discrimination than nonmusician children. Meanwhile, the EEG response of musicians to the two kinds of stimuli is also significantly different from that of nonmusicians, showing more mature patterns of ERP (stronger average P3a amplitude, smaller average LDN amplitude). The results suggested that music training can promote the development of lexical tone processing. In addition, the EEG response of musicians to lexical tones is stronger than that of nonmusicians only in the left hemisphere. This lateralization may indicate that the music training may not only enhance the neural response to lexical tone changes, but also promote the maturity of the neural networks specific for lexical tone.

Study 2 indicated that better musical pitch processing is related to better lexical tone perception. So if the development of musical pitch processing is abnormal, how will it affect lexical tone processing in tonal language speakers? In Study 3, we examined the processing of musical pitch and lexical tones in Mandarin speakers with congenital amusia (a developmental disorder typically show deficits in musical pitch processing). The study adopted the same paradigm as those in studies 1 and 2. We measured musical pitch and lexical tone discrimination in both amusics and music intact controls, and all participants' EEG responses to changes in musical pitch or lexical tone were recorded. The results showed that amusics’ discrimination of musical pitch and lexical tone was significantly weaker than control group, indicating that deficits in musical pitch processing might affect speech perception. The EEG results showed that the P3a components induced by musical pitch and lexical tone changes were weaker in amusics than in controls, suggesting that the deficits in musical pitch and lexical tone discrimination may be related to the weakened neural response to auditory pitch information. Interestingly, the results of time-frequency analysis showed that amusics only exhibited a decrease in the stability of the EEG response to music pitch (inter-trial coherence), while the stability of the EEG response to lexical tones was not different from control group. Meanwhile, the performance of lexical tone discrimination is also significantly higher than musical pitch discrimination. These findings suggested that although lexical tone processing of Mandarin speakers with amusia is affected by their deficits in musical pitch processing, Mandarin-speaking amusics still develop a relatively stable neural network and retains the ability of lexical tone discrimination to some extent.

Finally, on the basis of exploring the characteristics of the development trajectory of lexical tone perception, we try to further study the brain mechanism of the development of lexical tone perception from the perspective of the white matter neural connections, and analyze the neural manifestations related to the effect of changes in musical pitch processing on lexical tone perception. In Study 4, we focused on the bilateral arcuate fasciculus. The arcuate fasciculus is an important neural connection connecting the dorsal pathway of phonological processing (Hickok & Poeppel, 2007), connecting the two brain regions important for pitch processing - the prefrontal and temporal lobes   (Nan & Friederici, 2013; Peretz, 2016). Arcuate fasciculus is closely related to phonological processing (Su, Zhao, et al., 2018), and its development process runs through adolescence (Paus et al., 1999). Therefore, the study of arcuate fasciculus can reveal the brain mechanisms underlying the development of lexical tone perception. In Study 4, we used diffusion tensor imaging to analyze the difference in the arcuate fasciculus between amusics and controls. In this study, we tried to explore the brain mechanism of the development of lexical tone perception and the neural basis of the influence of abnormal musical pitch processing on lexical tone perception. The results showed that the volume of right fronto-parietal connection in amusics was significantly lower than in controls. Meanwhile, the fractional anisotropy of the right parieto-temporal connection in amusics was significantly higher than in controls. The results suggested that the abnormal musical pitch and lexical tone processing in amusics might be related to abnormal fronto-parieto-temporal network. In addition, the fractional anisotropy of the left arcuate fasciculus connecting frontal and temporal areas in amusics showed a significant negative correlation with their performances of tone test, but there was no significant difference between the groups. This indicates that the deficit of lexical tone processing in amusia is related to altered connectivity of the left dorsal pathway. The differences between the amusics and the controls were mainly observed on the right hemisphere, which was related to the disorder of the musical pitch processing. However, the abnormality of connectivity on the left hemisphere which was related to the processing of lexical tones did not reach a significant level, which was consistent with the results of experiment three, indicating that the influence of musical pitch deficits in amusics on the development of lexical tone perception may be limited, and the development trajectories of lexical tone and musical pitch processing do not completely coincide. The results of Study 4 suggest that the left arcuate fasciculus in the native tonal language speakers may be related to lexical tone perception, and the relationship between musical pitch processing and lexical tone perception may also be based on arcuate fasciculus to a certain extent.

In short, this project explored the characteristics of the development of lexical tone perception and investigated the influence of musical pitch processing on the development of lexical tone perception through two aspects (musical expertise and musical abnormality). Finally, we use diffusion tensor imaging to explore the neural basis of musical pitch processing’s influence on lexical tone development. Our research revealed that the development of lexical tone perception is closely related to the development of reading ability, but the development of lexical tone perception itself is still immature in the upper grades (9-11 years old) of primary schools. For 9-year-old school-age children, children with musical experience have stronger lexical tone discrimination and neural responses to lexical tone changes than nonmusician children. For amusics speaking Mandarin, the abnormality of musical pitch processing has affected the lexical tone processing as reflected by the poor performance of lexical tone discrimination and weakened the neural response towards lexical tone changes. Finally, the abnormalities of musical pitch and lexical tone processing are related to the abnormality of the arcuate fasciculus. The connectivity of left arcuate fasciculus is specifically related to the lexical tone perception in amusics. Based on results of this project, future researchers can conduct follow-up research on three issues: (1) The development trajectory of lexical tone perception in tonal language speakers. (2) The influence of musical pitch processing on lexical tone perception at different stages of lexical tone development. (3) The neural basis of lexical tone development and its relationship with neural networks for musical pitch processing. At the same time, follow-up longitudinal researches are necessary to verify and supplement the existing results of this project.