npj Science of Learning最新文献

筛选
英文 中文
Learning and navigating digitally rendered haptic spatial layouts 学习和浏览数字渲染的触觉空间布局
IF 4.2 1区 心理学
npj Science of Learning Pub Date : 2023-12-16 DOI: 10.1038/s41539-023-00208-4
Ruxandra I. Tivadar, Benedetta Franceschiello, Astrid Minier, Micah M. Murray
{"title":"Learning and navigating digitally rendered haptic spatial layouts","authors":"Ruxandra I. Tivadar, Benedetta Franceschiello, Astrid Minier, Micah M. Murray","doi":"10.1038/s41539-023-00208-4","DOIUrl":"https://doi.org/10.1038/s41539-023-00208-4","url":null,"abstract":"<p>Learning spatial layouts and navigating through them rely not simply on sight but rather on multisensory processes, including touch. Digital haptics based on ultrasounds are effective for creating and manipulating mental images of individual objects in sighted and visually impaired participants. Here, we tested if this extends to scenes and navigation within them. Using only tactile stimuli conveyed via ultrasonic feedback on a digital touchscreen (i.e., a digital interactive map), 25 sighted, blindfolded participants first learned the basic layout of an apartment based on digital haptics only and then one of two trajectories through it. While still blindfolded, participants successfully reconstructed the haptically learned 2D spaces and navigated these spaces. Digital haptics were thus an effective means to learn and translate, on the one hand, 2D images into 3D reconstructions of layouts and, on the other hand, navigate actions within real spaces. Digital haptics based on ultrasounds represent an alternative learning tool for complex scenes as well as for successful navigation in previously unfamiliar layouts, which can likely be further applied in the rehabilitation of spatial functions and mitigation of visual impairments.</p>","PeriodicalId":48503,"journal":{"name":"npj Science of Learning","volume":"81 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2023-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138683528","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"心理学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Seeking the neural representation of statistical properties in print during implicit processing of visual words 在视觉单词的内隐加工过程中寻求印刷品统计属性的神经表征
IF 4.2 1区 心理学
npj Science of Learning Pub Date : 2023-12-16 DOI: 10.1038/s41539-023-00209-3
Jianyi Liu, Tengwen Fan, Yan Chen, Jingjing Zhao
{"title":"Seeking the neural representation of statistical properties in print during implicit processing of visual words","authors":"Jianyi Liu, Tengwen Fan, Yan Chen, Jingjing Zhao","doi":"10.1038/s41539-023-00209-3","DOIUrl":"https://doi.org/10.1038/s41539-023-00209-3","url":null,"abstract":"<p>Statistical learning (SL) plays a key role in literacy acquisition. Studies have increasingly revealed the influence of distributional statistical properties of words on visual word processing, including the effects of word frequency (lexical level) and mappings between orthography, phonology, and semantics (sub-lexical level). However, there has been scant evidence to directly confirm that the statistical properties contained in print can be directly characterized by neural activities. Using time-resolved representational similarity analysis (RSA), the present study examined neural representations of different types of statistical properties in visual word processing. From the perspective of predictive coding, an equal probability sequence with low built-in prediction precision and three oddball sequences with high built-in prediction precision were designed with consistent and three types of inconsistent (orthographically inconsistent, orthography-to-phonology inconsistent, and orthography-to-semantics inconsistent) Chinese characters as visual stimuli. In the three oddball sequences, consistent characters were set as the standard stimuli (probability of occurrence <i>p</i> = 0.75) and three types of inconsistent characters were set as deviant stimuli (<i>p</i> = 0.25), respectively. In the equal probability sequence, the same consistent and inconsistent characters were presented randomly with identical occurrence probability (<i>p</i> = 0.25). Significant neural representation activities of word frequency were observed in the equal probability sequence. By contrast, neural representations of sub-lexical statistics only emerged in oddball sequences where short-term predictions were shaped. These findings reveal that the statistical properties learned from long-term print environment continues to play a role in current word processing mechanisms and these mechanisms can be modulated by short-term predictions.</p>","PeriodicalId":48503,"journal":{"name":"npj Science of Learning","volume":"5 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2023-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138683614","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"心理学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Does students’ awareness of school-track-related stereotypes exacerbate inequalities in education? 学生对与学校轨道相关的陈规定型观念的认识是否会加剧教育中的不平等?
IF 4.2 1区 心理学
npj Science of Learning Pub Date : 2023-12-14 DOI: 10.1038/s41539-023-00203-9
Lisa Bardach, Claudia Neuendorf, Kou Murayama, Thorsten Fahrbach, Michel Knigge, Benjamin Nagengast, Ulrich Trautwein
{"title":"Does students’ awareness of school-track-related stereotypes exacerbate inequalities in education?","authors":"Lisa Bardach, Claudia Neuendorf, Kou Murayama, Thorsten Fahrbach, Michel Knigge, Benjamin Nagengast, Ulrich Trautwein","doi":"10.1038/s41539-023-00203-9","DOIUrl":"https://doi.org/10.1038/s41539-023-00203-9","url":null,"abstract":"<p>Early ability tracking increases inequalities in education. It has been proposed that the awareness of negative school-track-related stereotypes contributes to educational inequalities, as stereotype awareness interferes with students’ abilities to thrive, particularly those in lower, stigmatized tracks. The present study tested this assumption in a sample of 3880 German secondary school students from three tracks, who were assessed four times on stereotype awareness regarding their own school track and academic outcomes (achievement, engagement, self-concept) between Grades 5 and 8. Students in the lowest track reported higher levels of stereotype awareness than higher track students or students attending a combined track. Stereotype awareness increased across time in all tracks. Contrary to our preregistered hypotheses, however, the results from multigroup models revealed that (changes in) stereotype awareness were not more strongly related to (changes in) most outcomes in the lowest track in comparison with the other two tracks.</p>","PeriodicalId":48503,"journal":{"name":"npj Science of Learning","volume":"173 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138683389","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"心理学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
The two-faced process of learning and the importance of Janus-faced solutions 双面学习过程和扬努斯面解决方案的重要性
IF 4.2 1区 心理学
npj Science of Learning Pub Date : 2023-12-14 DOI: 10.1038/s41539-023-00210-w
Robin Samuelsson
{"title":"The two-faced process of learning and the importance of Janus-faced solutions","authors":"Robin Samuelsson","doi":"10.1038/s41539-023-00210-w","DOIUrl":"https://doi.org/10.1038/s41539-023-00210-w","url":null,"abstract":"Significant developments have been made to our understanding of how children learn, putting essential pieces to the puzzle of what it means to be human. Theories of learning are, however, headed in diverging directions, and this perspective paper argues that this dispersion can recapitulate recurring schisms in developmental and learning sciences about learning as a predominantly individually constructed or socially transferred process. It is argued that this opposition is unnecessary and that an encompassing understanding of learning should consider both directions. This conciliatory approach considers how humans learn from others and what is known while exploring new solutions. This is important for understanding learning in childhood, seeing learning as a simultaneously individual and social process where humans actively explore and exploit knowledge about the world around them. Framing learning by the metaphor of a Janus face, looking back at what is known while exploring new knowledge, becomes illuminating for understanding learning and provides an essential background for designing educational practices based on active learning.","PeriodicalId":48503,"journal":{"name":"npj Science of Learning","volume":"19 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138683529","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"心理学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Language experience matters for the emergence of early numerical concepts 语言经验对早期数字概念的形成至关重要
IF 4.2 1区 心理学
npj Science of Learning Pub Date : 2023-12-09 DOI: 10.1038/s41539-023-00202-w
Stacee Santos, Hiram Brownell, Marie Coppola, Anna Shusterman, Sara Cordes
{"title":"Language experience matters for the emergence of early numerical concepts","authors":"Stacee Santos, Hiram Brownell, Marie Coppola, Anna Shusterman, Sara Cordes","doi":"10.1038/s41539-023-00202-w","DOIUrl":"https://doi.org/10.1038/s41539-023-00202-w","url":null,"abstract":"<p>Research has shown a link between the acquisition of numerical concepts and language, but exactly how linguistic input matters for numerical development remains unclear. Here, we examine both symbolic (number word knowledge) and non-symbolic (numerical discrimination) numerical abilities in a population in which access to language is limited early in development—oral deaf and hard of hearing (DHH) preschoolers born to hearing parents who do not know a sign language. The oral DHH children demonstrated lower numerical discrimination skills, verbal number knowledge, conceptual understanding of the word “more”, and vocabulary relative to their hearing peers. Importantly, however, analyses revealed that group differences in the numerical tasks, but not vocabulary, disappeared when differences in the amount of time children had had auditory access to spoken language input via hearing technology were taken into account. Results offer insights regarding the role language plays in emerging number concepts.</p>","PeriodicalId":48503,"journal":{"name":"npj Science of Learning","volume":"67 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2023-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138561659","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"心理学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Arithmetic skills are associated with left fronto-temporal gray matter volume in 536 children and adolescents 536 名儿童和青少年的算术能力与左额叶-颞叶灰质体积有关
IF 4.2 1区 心理学
npj Science of Learning Pub Date : 2023-12-08 DOI: 10.1038/s41539-023-00201-x
Nurit Viesel-Nordmeyer, Jérôme Prado
{"title":"Arithmetic skills are associated with left fronto-temporal gray matter volume in 536 children and adolescents","authors":"Nurit Viesel-Nordmeyer, Jérôme Prado","doi":"10.1038/s41539-023-00201-x","DOIUrl":"https://doi.org/10.1038/s41539-023-00201-x","url":null,"abstract":"<p>There are large individual differences in arithmetic skills. Although a number of brain-wide association studies have attempted to identify the neural correlates of these individual differences, studies have focused on relatively small sample sizes and have yielded inconsistent results. In the current voxel-based morphometry study, we merged six structural imaging datasets of children and adolescents (from 7.5 to 15 years) whose levels of arithmetic skills were assessed, leading to a combined sample of <i>n</i> = 536. Controlling for individual differences in age, gender, as well as language, and intelligence, we found a unique positive relation between arithmetic skill and gray matter volume in the left inferior frontal gyrus (IFG) and middle temporal gyrus (MTG). Our results suggest that individual differences in arithmetic skills are associated with structural differences in left fronto-temporal areas, rather than in regions of the parietal cortex and hippocampus that are often associated with arithmetic processing.</p>","PeriodicalId":48503,"journal":{"name":"npj Science of Learning","volume":"195 1","pages":""},"PeriodicalIF":4.2,"publicationDate":"2023-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138561668","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"心理学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Disentangling sensory precision and prior expectation of change in autism during tactile discrimination. 孤独症触觉辨别过程中感官精确性和先验预期变化的分离。
IF 4.2 1区 心理学
npj Science of Learning Pub Date : 2023-12-06 DOI: 10.1038/s41539-023-00207-5
Laurie-Anne Sapey-Triomphe, Gaëtan Sanchez, Marie-Anne Hénaff, Sandrine Sonié, Christina Schmitz, Jérémie Mattout
{"title":"Disentangling sensory precision and prior expectation of change in autism during tactile discrimination.","authors":"Laurie-Anne Sapey-Triomphe, Gaëtan Sanchez, Marie-Anne Hénaff, Sandrine Sonié, Christina Schmitz, Jérémie Mattout","doi":"10.1038/s41539-023-00207-5","DOIUrl":"10.1038/s41539-023-00207-5","url":null,"abstract":"<p><p>Predictive coding theories suggest that core symptoms in autism spectrum disorders (ASD) may stem from atypical mechanisms of perceptual inference (i.e., inferring the hidden causes of sensations). Specifically, there would be an imbalance in the precision or weight ascribed to sensory inputs relative to prior expectations. Using three tactile behavioral tasks and computational modeling, we specifically targeted the implicit dynamics of sensory adaptation and perceptual learning in ASD. Participants were neurotypical and autistic adults without intellectual disability. In Experiment I, tactile detection thresholds and adaptation effects were measured to assess sensory precision. Experiments II and III relied on two-alternative forced choice tasks designed to elicit a time-order effect, where prior knowledge biases perceptual decisions. Our results suggest a subtler explanation than a simple imbalance in the prior/sensory weights, having to do with the dynamic nature of perception, that is the adjustment of precision weights to context. Compared to neurotypicals, autistic adults showed no difference in average performance and sensory sensitivity. Both groups managed to implicitly learn and adjust a prior that biased their perception. However, depending on the context, autistic participants showed no, normal or slower adaptation, a phenomenon that computational modeling of trial-to-trial responses helped us to associate with a higher expectation for sameness in ASD, and to dissociate from another observed robust difference in terms of response bias. These results point to atypical perceptual learning rather than altered perceptual inference per se, calling for further empirical and computational studies to refine the current predictive coding theories of ASD.</p>","PeriodicalId":48503,"journal":{"name":"npj Science of Learning","volume":"8 1","pages":"54"},"PeriodicalIF":4.2,"publicationDate":"2023-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10700558/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138499850","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"心理学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Deliberately making miskates: Behavioural consistency under win maximization and loss maximization conditions. 故意犯错误:收益最大化和损失最大化条件下的行为一致性。
IF 4.2 1区 心理学
npj Science of Learning Pub Date : 2023-12-06 DOI: 10.1038/s41539-023-00206-6
Yajing Zhang, Thi Kim Truc Huynh, Benjamin James Dyson
{"title":"Deliberately making miskates: Behavioural consistency under win maximization and loss maximization conditions.","authors":"Yajing Zhang, Thi Kim Truc Huynh, Benjamin James Dyson","doi":"10.1038/s41539-023-00206-6","DOIUrl":"10.1038/s41539-023-00206-6","url":null,"abstract":"<p><p>We argue that the feedback traditionally used to indicate negative outcomes causes future detrimental performance because of the default goal of win maximization. In gaming paradigms where participants intentionally performed as well (win maximization) and as poorly (loss maximization) as possible, we showed a double dissociation where actions following wins were more consistent during win maximization, but actions following losses were more consistent during loss maximization. This broader distinction between goal-congruent and goal-incongruent feedback suggests that individuals are able to flexibly redefine their definition of 'success', and provide a reconsideration of the way we think about 'losing'.</p>","PeriodicalId":48503,"journal":{"name":"npj Science of Learning","volume":"8 1","pages":"55"},"PeriodicalIF":4.2,"publicationDate":"2023-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10700323/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138499849","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"心理学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
The relationship of school performance with self-control and grit is strongly genetic and weakly causal. 学校成绩与自我控制和毅力的关系具有强遗传和弱因果关系。
IF 4.2 1区 心理学
npj Science of Learning Pub Date : 2023-12-04 DOI: 10.1038/s41539-023-00198-3
Sofieke T Kevenaar, Elsje van Bergen, Albertine J Oldehinkel, Dorret I Boomsma, Conor V Dolan
{"title":"The relationship of school performance with self-control and grit is strongly genetic and weakly causal.","authors":"Sofieke T Kevenaar, Elsje van Bergen, Albertine J Oldehinkel, Dorret I Boomsma, Conor V Dolan","doi":"10.1038/s41539-023-00198-3","DOIUrl":"10.1038/s41539-023-00198-3","url":null,"abstract":"<p><p>The non-cognitive skills self-control and grit are often considered predictors of school performance, but whether this relationship is causal remains unclear. We investigated the causality of this association using a twin design. Specifically, we evaluated the direct impact of self-control and grit on school performance, while controlling for genetic or environmental influences common to all three traits (i.e., confounding). Teachers of 4891 Dutch 12-year-old twin pairs (of which 3837 were complete pairs) completed a survey about school performance (school grades), self-control (ASEBA self-control scale), and the perseverance aspect of grit. Our analysis aimed to determine the direct impact of self-control and grit on school performance, while simultaneously controlling for genetic or environmental confounding. Establishing the regression relationship corrected for confounding supports the interpretation of the regression relationship as causal. In all analyses, we corrected for sex, rater bias of the teachers, and parental socioeconomic status. Initially, in the standard regression, self-control, and grit explained 28.4% of the school performance variance. However, allowing for genetic confounding (due to genetic pleiotropy) revealed that most of this association could be attributed to genetic influences that the three traits share. In the presence of genetic pleiotropy, the phenotypic regression of school performance on self-control and grit accounted for only 4.4% (i.e., the effect size association with the causal hypothesis). In conclusion, self-control and grit predict school performance primarily due to genetic pleiotropy, with a much smaller causal effect (R<sup>2</sup> = 4.4%). This suggests that interventions targeting self-control and grit alone may yield limited improvements in school performance.</p>","PeriodicalId":48503,"journal":{"name":"npj Science of Learning","volume":"8 1","pages":"53"},"PeriodicalIF":4.2,"publicationDate":"2023-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10696063/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138483267","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"心理学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Prevalence of undiagnosed dyslexia in African-American primary school children. 非裔美国小学生未确诊阅读障碍的患病率。
IF 4.2 1区 心理学
npj Science of Learning Pub Date : 2023-12-02 DOI: 10.1038/s41539-023-00204-8
Laura Cassidy, Kayla Reggio, Bennett A Shaywitz, Sally E Shaywitz
{"title":"Prevalence of undiagnosed dyslexia in African-American primary school children.","authors":"Laura Cassidy, Kayla Reggio, Bennett A Shaywitz, Sally E Shaywitz","doi":"10.1038/s41539-023-00204-8","DOIUrl":"10.1038/s41539-023-00204-8","url":null,"abstract":"<p><p>Dyslexia is among the most common neurodevelopmental disorders in children, yet despite its high prevalence all too frequently goes undiagnosed. Consequently dyslexic children all too often fail to receive effective reading interventions. Here we report our findings from a study using a teacher completed evidence-based dyslexia screener to first screen then test predominantly African-American children in grades kindergarten through second grade in two inner city public charter schools in New Orleans. Almost half (49.2%) of the children screened as at risk for dyslexia and of these the majority were found to be dyslexic on more detailed testing. Our results suggest that large numbers of African-American students with dyslexia may be overlooked in schools.</p>","PeriodicalId":48503,"journal":{"name":"npj Science of Learning","volume":"8 1","pages":"52"},"PeriodicalIF":4.2,"publicationDate":"2023-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10693615/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138479000","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"心理学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
0
×
引用
GB/T 7714-2015
复制
MLA
复制
APA
复制
导出至
BibTeX EndNote RefMan NoteFirst NoteExpress
×
提示
您的信息不完整,为了账户安全,请先补充。
现在去补充
×
提示
您因"违规操作"
具体请查看互助需知
我知道了
×
提示
确定
请完成安全验证×
相关产品
×
本文献相关产品
联系我们:info@booksci.cn Book学术提供免费学术资源搜索服务,方便国内外学者检索中英文文献。致力于提供最便捷和优质的服务体验。 Copyright © 2023 布克学术 All rights reserved.
京ICP备2023020795号-1
ghs 京公网安备 11010802042870号
Book学术文献互助
Book学术文献互助群
群 号:481959085
Book学术官方微信