同伴交往对青少年的发展有着重要的作用，社会退缩个体将自己孤立于同伴互动之外，容易被同伴群体拒绝和排斥，感知到的友谊质量较低。羞怯和社交淡漠是社会退缩的两种主要亚类型，羞怯指个体处于新异的社会环境或感知到自己会被社会评价时产生警觉和紧张，进而远离社会互动，具有高社交趋近和高社交回避动机，社交淡漠指个体对社会交往不感兴趣，偏好独自活动，这种偏好和对社交环境的害怕无关，具有低社交趋近和低社交回避动机。过往研究发现，羞怯和社交淡漠的适应意义存在中西方差异，在社会变迁的背景下，羞怯和社交淡漠对当前中国青少年同伴关系的作用模式更为复杂。因此，当前中国社会背景下羞怯、社交淡漠对青少年不同水平同伴关系的影响及其内部机制值得深入探讨。由于退缩的动机不同，羞怯和社交淡漠对自我的认识和对人际互动的态度和预期可能存在差异，进而影响其群体水平同伴关系和关系水平友谊质量。本研究从自我特征和人际特征切入，结合实验法和脑成像技术，深入探讨羞怯、社交淡漠对中国青少年不同水平同伴关系的影响机制。

本论文由三个研究组成。研究一为基础研究，采用两年追踪数据，探讨羞怯、社交淡漠对青少年不同水平同伴关系的同时效应和延时效应。研究二包括两个子研究，分别考察自我特征(自我控制和自尊)和人际特征(人际信任和共情)在羞怯、社交淡漠与青少年不同水平同伴关系间的作用。研究三在研究二的基础上，结合fNIRS技术，通过五个实验全面系统考察羞怯、社交淡漠青少年在自我相关(自我评价、自我控制任务)和人际相关(人际信任、共情和同伴实时互动任务)加工过程中的神经活动特征，并进一步考察神经活动对不同水平同伴关系的预测作用，深入探讨羞怯、社交淡漠影响青少年不同水平同伴关系的神经机制。

本研究的具体结论如下：

1. 羞怯、社交淡漠对青少年不同水平同伴关系的影响

(1) 羞怯和社交淡漠能显著预测同一时间点和间隔一年后青少年群体水平同伴关系，羞怯正向预测同伴接纳和同伴排斥，负向预测同伴拒绝；社交淡漠正向预测同伴拒绝和同伴排斥，负向预测同伴接纳。羞怯对男生的消极影响大于女生，对城市地区青少年的消极影响大于农村地区；社交淡漠对农村地区青少年的消极影响大于城市地区。

(2) 社交淡漠能显著负向预测同一时间点和间隔一年后青少年关系水平友谊质量，对男生的消极影响大于女生；羞怯对关系水平友谊质量作用不显著。

2. 自我特征(自我控制、自尊)和人际特征(人际信任、共情)在羞怯、社交淡漠和青少年不同水平同伴关系之间的作用

(1) 自我特征(自我控制、自尊)的作用体现为：

羞怯和社交淡漠可以通过自我控制的单独中介影响青少年同一时间点和间隔一年后的群体水平同伴关系，也能通过自我控制和自尊的链式中介影响同一时间点和间隔一年后的关系水平友谊质量；羞怯和社交淡漠在中介路径上存在显著差异，羞怯可以正向预测自我控制，而社交淡漠负向预测自我控制；以上路径不存在显著的性别差异和城乡地区差异。

(2) 人际特征(人际信任、共情)的作用体现为：

羞怯可以通过共情的单独中介影响同一时间点和间隔一年后的关系水平友谊质量，社交淡漠可以通过人际信任的单独中介、共情的单独中介，人际信任到共情的链式中介作用影响同一时间点和间隔一年后的关系水平友谊质量；羞怯和社交淡漠在中介路径上差异显著，羞怯正向预测共情，对人际信任无显著作用，社交淡漠负向预测人际信任和共情；以上路径不存在显著的性别差异和城乡地区差异。

3. 羞怯、社交淡漠影响青少年不同水平同伴关系的神经机制

通过fNIRS技术考察羞怯、社交淡漠青少年在自我相关(自我评价、自我控制任务)和人际相关(人际信任、共情和同伴实时互动任务)加工过程中的神经活动特征发现：

(1) 自我评价任务中，与非社会退缩青少年相比，羞怯和社交淡漠青少年在左侧中央前回的激活水平更高；羞怯青少年在消极评价自我时右侧额上回的激活和社交淡漠青少年在积极评价自我时右侧额下回的激活与其群体水平同伴关系正向关联。

(2) 自我控制任务中，羞怯青少年在右侧额上回的激活显著高于社交淡漠和非社会退缩青少年；社交淡漠青少年在一致条件下的右侧额下回的激活和不一致条件下的右侧中央后回的激活与其群体水平同伴关系存在显著关联。

(3) 人际信任任务中，羞怯和社交淡漠青少年在左侧颞中回的激活显著高于非社会退缩青少年，羞怯青少年在左侧缘上回的激活效应显著低于非社会退缩青少年；羞怯青少年在投资陌生人和投资朋友条件下左侧缘上回的激活与其关系水平友谊质量负向关联，社交淡漠青少年在投资朋友条件下右侧中央前回的激活与其关系水平友谊质量正向关联。

(4) 共情任务中，在认知共情效应和情绪共情效应上，羞怯青少年在右侧顶下小叶的激活均显著低于非社会退缩青少年；羞怯青少年在认知共情和情绪共情条件下右侧顶下小叶的激活与其关系水平友谊质量负向关联。

(5) 同伴实时互动任务中，在合作效应和竞争效应上，社交淡漠青少年在左侧额下回的激活均显著高于羞怯和非社会退缩青少年；羞怯青少年在合作和竞争条件下左侧额下回的激活与其关系水平友谊质量正向关联，社交淡漠青少年在独自条件下左侧额下回的激活与其群体水平同伴关系负向关联。

本论文深入探讨了中国社会背景下羞怯、社交淡漠对青少年不同水平同伴关系的影响，结合问卷法和实验法系统考察了自我特征和人际特征在其中的作用，发现了羞怯、社交淡漠青少年自我和人际相关神经活动与不同水平同伴关系的关联，并为羞怯、社交淡漠的差异提供了神经影像学证据。研究结果全面揭示了羞怯、社交淡漠对青少年不同水平同伴关系的影响及机制，构建了羞怯、社交淡漠影响不同水平同伴关系的整合模型，推动了社会退缩领域理论体系的发展，为羞怯、社交淡漠青少年的干预和辅导提供了实证依据。

Peer communication plays an important role in the development of adolescents. Individuals with social withdrawal isolate themselves from peer interaction, might be rejected and excluded by peer groups, and perceive friendships as of lower quality. Shyness and unsociability are the two main subtypes of social withdrawal. Shyness refers to wariness and self-consciousness in unfamiliar social situations and instances of perceived social evaluation. Unsociability refers to playing alone due to social disinterest. Shy individuals have a high social approach motivation, as well as a high social avoidance motivation, meanwhile, unsociable individuals have a low social approach motivation, as well as a low social avoidance motivation. Previous studies have found differences in the adaptive meanings of shyness and unsociability between Chinese and Western countries. In the context of social change, the effects of shyness and unsociability on peer relationships among Chinese adolescents are more complex. Therefore, the influence of shyness and unsociability on adolescents' peer relationship at different levels in the current Chinese cultural background and its internal mechanism are worthy of in-depth discussion. Due to the different motivations of withdrawal, shyness and unsociability may have different self-knowledge and attitudes and expectations towards interpersonal interactions, which in turn affect their group-level peer relationships and relationship-level friendship. Based on self-characteristics and interpersonal characteristics, combined with experimental methods and brain imaging technology, this study explored the mechanism of shyness and unsociability affecting peer relationships at different levels among Chinese adolescents.

The present research consists of three studies. Study 1, using a two-years of follow-up research, to explore the simultaneous and delayed effects of shyness and unsociability on adolescents at different levels of peer relationship. Study 2, consisted of two sub-studies, which examined the role of self-characteristics (self-control and self-esteem) and interpersonal characteristics (interpersonal trust and empathy) on shyness, unsociability, and peer relationship at different levels. Study 3, based on the results of study 2, combined fNIRS technology, conducted five experiments to comprehensively and systematically investigate the neural activity characteristics of shy and unsociable adolescents during self-related (self-evaluation task, self-control task) and interpersonal related (trust game, empathy task, and real-time peer interaction task) processing. The predictive effect of neural activity on different levels of peer relationships was further investigated, and the neural mechanism of shyness and unsociability affecting different levels of peer relationships was further explored.

The main conclusions of the present research are as follows:

1. The influence of shyness and unsociability on adolescents' peer relationship at different levels:

(1) Shyness and unsociability can significantly predict peer relationship at the same time point and one year after the interval, and shyness can positively predict peer acceptance and peer exclusion and negatively predict peer rejection. Unsociabi-

lity positively predicted peer rejection and peer exclusion, and negatively predicted peer acceptance. The negative effect of shyness on boys was greater than that on girls, and the negative effect of shyness on adolescents in urban areas was greater than that in rural areas. The negative effect of unsociability on adolescents in rural areas was greater than that in urban areas.

(2) Unsociability can significantly negatively predict the friendship quality of adolescents at the same time point and one year after the interval, and the negative effect on boys was greater than that on girls. Shyness had no significant effect on the friendship quality.

2. The role of self-characteristics (self-control, self-esteem) and interpersonal characteristics (interpersonal trust, empathy) in shyness, unsociability, and adolescents' different levels of peer relationship:

(1) The role of self-characteristics (self-control, self-esteem):

First, shyness and unsociability can affect adolescents' peer relationship at the same time point and at the group level one year later through self-control, and can also affect friendship quality at the same time point and at the relationship level one year later through the chain mediation of self-control and self-esteem; Second, there were significant differences between shyness and unsociability in the indirect path. Shyness can positively predict self-control, while unsociability can negatively predict self-control. Third, there was no significant gender difference or urban/rural difference in the above paths.

(2) The role of interpersonal characteristics (interpersonal trust and empathy):

First, shyness can influence friendship quality at the same time point and at the relationship level one year later through the mediation of empathy; Second, unsociability can affect the friendship quality at the same time point and at the relationship level one year later through the mediation of interpersonal trust, the mediation of empathy, and the chain mediation of interpersonal trust to empathy. Third, there were significant differences between shyness and unsociability in the three paths. Shyness positively predicted empathy, but had no significant effect on interpersonal trust, while unsociability negatively predicted empathy and interpersonal trust. Fourth, there was no significant gender difference or urban/rural difference in the above paths.

3. The neural mechanism of shyness and unsociability affecting different levels of peer relationships among adolescents:

fNIRS technique was used to investigate the neural activity characteristics of shy, unsociable, and non-social withdrawal adolescents in self-evaluation task, self-control task, trust game, empathy task, and real-time peer interaction task.

(1) During the self-evaluation task, compared with the non-social withdrawal group, the activation of the left precentral gyrus was higher in the shy and unsociable group; The activation of the right superior frontal gyrus during negative self-evaluation in shy group and the activation of the right inferior frontal gyrus during positive self-evaluation in unsociability group were positively correlated with their group-level peer relationship.

(2) During the self-control task, shy group showed significantly higher activation in the right medial superior frontal gyrus than unsociable and non-social withdrawal group. For unsociable group, activation in the right inferior frontal gyrus in congruent condition and activation in the right postcentral gyrus in incongruent condition were significantly correlated with group-level peer relationships.

(3) During the trust game, the activation of left middle temporal gyrus in shy and unsociable group was higher than that of non-social withdrawal group, and the activation of left supramarginal gyrus in shy group was lower than that of non-social withdrawal group. The activation of the left supramargial gyrus in shy group was significantly correlated with friendship quality. The activation of the right precentral gyrus in unsociable group was positively correlated with friendship quality under the condition of invest to friends.

(4) During the empathy task, for both cognitive empathy and emotional empathy effects, the activation of shyness group was significantly lower than that of non-social withdrawal group. The activation of the right inferior parietal lobule in shy group was negatively correlated with friendship quality.

(5) During peer real-time interaction, for both cooperation and competition effects, the activation of the left inferior frontal gyrus in unsociability group was significantly higher than that in shy and non-social withdrawal group. The activation of left inferior frontal gyrus in shy group under cooperation and competition conditions was positively correlated with friendship quality, and the activation of left inferior frontal gyrus in unsociable group under solitary condition was negatively correlated with group-level peer relationship.

The present research clarified the effect of shyness and unsociability on peer relationship at different levels among Chinese adolescents. Combined with questionnaire and experimental methods, this research systematically investigated the role of self-and interpersonal characteristics, and found the correlation between self-and interpersonal neural activities and different levels of peer relationships in shy and unsociable adolescents. Neuroimaging evidence for differences between shyness and unsociability was also provided. The results of present research comprehensively revealed the effects and mechanisms of shyness and unsociability on peer relationships at different levels in adolescents. An integrated model of shyness and unsociability on peer relationships at different levels was constructed, which promoted the development of the theoretical system in the field of social withdrawal and provided an empirical basis for the intervention and counseling of adolescents with shyness and unsociability.