新生儿语音感知的脑机制

语言能力是人类区别于动物最本质的能力之一。其中,语音加工是语言认知的核心功能,语音加工的脑机制是语言学及认知心理学关注和研究的重要课题。该领域已有的大部分研究主要关注成人、儿童青少年或婴儿如何加工和处理语音,目前我们对新生儿(人类出生28天内)的大脑是如何感知语音的尚不清楚。随着神经科学技术的发展,非侵入式的大脑活动测量技术被越来越多的用于考察新生儿的脑机制。研究发现,人类在新生儿时期就已经存在相对完善的语音加工神经系统。例如,感知超音段特征的关键脑区为右侧颞上回,检测音节序列结构的关键脑区为左侧额下回(Broca区)。本文分别从新生儿对音段和超音段特征的感知、对音节序列结构(包括序列边缘、重复结构、结构分割)的感知,以及对母语和外语感知的差异这三个方面,介绍新生儿对不同语音特征感知的大脑机制,并就此领域的研究发展方向做出了几点探讨。     

汉语声调认知加工的脑机制及语言经验的影响

汉语母语者对汉语声调的认知加工可分为亚词汇和词汇两种加工水平。亚词汇水平涉及对汉语声调的声学和语音加工,当无需主动注意参与时,现有研究在左右半球优势上尚未取得明确结论;当需要主动注意参与时,优势主要表现为左侧化,涉及左侧的布洛卡区、前运动区、前部脑岛、顶叶、顶枕联合区以及双侧听皮层附近脑区,这与语言加工双通路模型(HickokPoeppel,2007)中的背侧通路有很大重合。词汇水平涉及对汉语声调的识别,由双侧半球参与,顶叶、颞叶等部分脑区左侧优势更加明显,同时涉及颞中回等语言加工腹侧通路的核心区域。此外,个体对汉语声调认知加工的脑机制会受到语言经验的影响。     

汉语加工脑神经机制研究的新进展

随着脑科学研究手段的改进．人们对汉语加工的脑神经机制有了更多、更深入的了解。大量研究表明,汉语加工有不同于拼音语言加工的脑机制,在加工汉语时．激活的脑区和在加工拼音语言时激活的脑区不同．母语为汉语的人和母语为拼音语言的人在脑的形态结构上也存在显著差异。对汉语加工脑机制的研究有利于对音素和音节加工的皮层表征的分离,有助于揭示语言加工脑机制的普遍性和特殊性。     

汉-英儿童双语者母语和二语加工的相互作用:来自神经机制方面的证据

双语者语言加工的神经机制一直是语言认知神经科学研究关注的热点问题之一。前人研究多关注二语加工过程,较少研究母语加工神经网络与二语加工神经网络之间的相互作用;并且前人研究多以成人为被试,研究结果可能会受到发展成熟因素的影响。本研究中,28名汉英儿童双语者进行了两种语言条件下的语音判断任务和字形判断任务,在进行任务的同时进行了磁共振扫描。通过全脑分析、感兴趣区分析和相关分析,结果显示:1)汉语语音、字形加工和英语语音、字形加工激活了类似的脑区网络,但也存在差异。汉语特异脑区(根据Tan等人对汉英跨语言比较的元分析进行定义)右侧枕下回、梭状回以及左侧扣带回在英语语音、字形任务中都显著激活,英语语音任务还额外激活了汉语特异的左脑额中回和中央前回;英语特异脑区(根据Tan等人对汉英进行跨语言比较的元分析进行定义)左脑额内侧、额下回以及梭状回在汉语语音、字形加工中显著激活。2)儿童的英语熟练度越低,左脑扣带回(汉语特异脑区)在汉语语音和汉语字形任务中的激活越强;汉语熟练度越高,左脑额下回(英语特异脑区)在英语字形任务中的激活越强,左脑颞上回(英语特异脑区)在英语语音任务中的激活越弱。两个任务的结果一致说明:汉英双语者母语加工的神经网络与二语加工的神经网络之间存在相互作用,并且受到双语熟练度的调制。     

新生儿对语音的感知、辨别和学习

新生儿自娩出起便开始利用臻于成熟的听觉系统对语音的各要素进行大脑表征和学习记忆。考察新生儿语音加工特点,不仅能揭示语言功能在人类发展最初阶段的认知神经机制,还能对自闭症等神经发育性疾病的早期预警和临床诊断提供有价值的线索。我们回顾并总结了新生儿对语音的感知、辨别和学习以及语言发展对自闭症的预测作用,发现新生儿对特定语音存在感知偏好;新生儿具备独特的音素辨别能力;婴儿期语言加工的脑功能或结构指标对自闭症具有一定的预测价值。我们建议未来研究从三个方面开展工作。在基础研究方面：第一,严格控制语音材料的韵律因素,重新审查新生儿语言加工特征及大脑偏侧化问题;第二,揭示新生儿语音学习的认知神经机制以及睡眠的记忆巩固作用。在临床转化研究方面,以高风险自闭症新生儿为追踪对象,基于纵向多模态脑观测数据,建立疾病风险评估系统,揭示出生早期语言发展脑指标对自闭症的预测价值。     

婴儿情绪与社会认知相关的听觉加工

听觉是人类获得外部环境信息的主要感官之一,对情绪与社会认知相关听觉加工的发展有重要意义。在生命早期,新生儿、婴儿对情绪语音已有感知、分辨与识别能力并表现出对特定情绪的加工偏好;对人类语音、母语等带有社会属性声音也产生了加工偏好;在诸如面孔识别等社会认知能力的发展中,听觉也起到一定作用,听觉障碍则影响有关社会认知的发展。建议未来研究有更多纵向设计,结合多模态成像技术来更好地解决发展性问题。     

音乐绝对音高信息加工的脑机制

音乐绝对音高(absolute pitch, AP)一直是音乐心理学者感兴趣的问题。AP能力是一种特殊的音乐能力。ERP研究表明具有AP能力的群体只需较少的认知资源进行音高加工, 同时不同AP能力的加工机制也不同; 功能神经成像研究表明大脑左侧额叶背侧后部和左侧颞叶平面对AP加工发挥重要作用; 脑结构研究发现AP群体的某些脑区皮层厚度低于没有绝对音高能力(Non-AP)群体, 这可能与AP特殊的加工机制有关。AP能力形成需要先天遗传和后天环境的共同作用, 其相互作用的脑机制需结合行为遗传学的研究方法及成果。     

汉语作为第二语言学习的脑机制

国家兴,语言强。近年来,汉语作为第二语言学习的认知神经机制研究日渐增长,但汉语二语学习脑机制的系统归纳及相关理论模型仍处于起步阶段。基于汉语二语学习近20年的脑机制研究,以及最新二语学习脑机制的研究和理论,可以归纳主要发现为：1)汉语声调学习最初依赖右颞上回和右额下回,掌握后转而依赖左颞上回;2)汉字字形学习与双侧额下回及右梭状回有关,而汉字语音学习则与左颞顶叶区相关;3)汉语二语学习初期会依赖右脑重要脑区(额下回、梭状回等),随汉语能力的提升,这种依赖减弱。综上,汉语二语学习与右脑关系密切,经历了由右侧功能主导转向双侧化或者左侧化的动态大脑发展变化过程。汉语学习者所采取的二语学习方法及其语音听辨能力,会影响学习者的语言功能、脑结构及其脑功能网络连接方式。未来研究可以从被试语言背景、研究范式和内容、数据分析等角度出发,探寻汉语二语学习的有效方法,构建并完善汉语二语学习认知神经机制的相关理论模型。     

绝对音高加工的认知神经机制

绝对音高(absolute pitch,AP)是一种比较罕见的音高加工能力,具有特殊的认知和神经机制。事件相关电位研究表明AP音乐家进行音高命名时,工作记忆参与较少但涉及多个认知策略。功能神经成像研究发现左侧额叶背侧后部和左侧颞叶平面对AP音乐家非常重要,而准AP音乐家(quasi-AP)的某些右侧脑区的参与则反映其增加的音高加工负荷和难度。结构神经成像研究发现AP音乐家具有特殊的灰质结构形态及白质连接。未来研究有待将AP能力进一步分为"具有相对音高能力"与"没有相对音高能力"两类并观察相应的认知神经机制,并通过影像基因组学来探索基因多态性对AP能力的影响,以及有必要观察以声调语言为母语的音乐家进行音高加工的神经机制。     

语言理解中句法加工的脑机制

大量研究表明左侧额叶和颞叶的多个脑区与句法加工有关, 已有的理论模型分别从不同的角度对句法加工的脑机制进行了解释。通过文献比较与分析发现, 对句法加工的操作定义、实验任务、被试个体差异以及语言差异等均可能导致研究结果出现差异。在将来的研究中, 可以通过跨语言、多任务比较, 不同层面的句法加工的操作, 在方法上将个体功能定位分析与传统的组分析相结合, 以及从神经网络的角度来更准确和全面地揭示句法加工的脑机制。     

外显和内隐情绪韵律加工的脑机制：近红外成像研究

准确识别言语中的情绪韵律信息对社会交往非常重要。本研究采用功能近红外成像技术, 探索外显和内隐情绪加工条件下愤怒、恐惧、快乐三种情绪韵律加工过程中的大脑皮层神经活动。结果表明, 对愤怒、恐惧、快乐韵律进行特异性加工的脑区分别为左侧额极/眶额叶、右侧缘上回、左侧额下回, 其中右侧缘上回脑区同时受到情绪和任务的调控。此外, 右侧颞中回、颞下回和颞极在情绪外显任务中的激活明显强于内隐任务。本研究的结果部分支持了情绪韵律的层次模型, 也对该模型的第三层次, 即“额区对语音情绪信息的精细加工需要外显性情绪加工任务参与”提出了质疑。     

婴儿对语音和非语音的感知:认知和神经机制

婴儿听觉感知能力的发展对于他们未来的语言学习和社会化都具有重要意义。过去大量的研究主要关注语音感知方面,只有较少的研究将非语音感知纳入考虑之中,但了解非语音感知的特征和机制将有助于增加研究者对听觉加工以及儿童发育的认识。该文分别介绍了婴儿语音感知中的三种偏好——对语音、“婴儿语”和母语的偏好,并尝试着将非语音分为音乐、人类的非言语发声、环境声音三类进行阐述。通过对比这两大类声音的感知得到婴儿可能存在语音感知的左脑偏侧化和音乐感知的右脑偏侧化现象,但这也尚存争议,目前有特定领域模型、特定线索模型和脑网络模型三种理论对偏侧化现象的认知机制进行解释。     

Role of left posterior superior temporal gyrus in phonological processing for speech perception and production

Models of both speech perception and speech production typically postulate a processing level that involves some form of phonological processing. There is disagreement, however, on the question of whether there are separate phonological systems for speech input versus speech output. We review a range of neuroscientific data that indicate that input and output phonological systems partially overlap. An important anatomical site of overlap appears to be the left posterior superior temporal gyrus. We then present the results of a new event-related functional magnetic resonance imaging (fMRI) experiment in which participants were asked to listen to and then (covertly) produce speech. In each participant, we found two regions in the left posterior superior temporal gyrus that responded both to the perception and production components of the task, suggesting that there is overlap in the neural systems that participate in phonological aspects of speech perception and speech production. The implications for neural models of verbal working memory are also discussed in connection with our findings.     

汉语口语韵律的作用及其神经机制

汉语是一种声调语言, 在口语韵律表达中存在独特的特点。本项目利用汉语不同于非声调语言的特点, 探讨已有研究中尚未澄清的问题, 即汉语声调在早期自动加工中对语义激活的作用, 以及在不同认知阶段中, 汉语声调和语调加工的神经机制。这些问题是当前的研究热点, 但仍存在着各种分歧和激烈的争论。本项目拟采用ERP方法, 结合LORETA源定位技术, 通过不同的实验范式考察以下内容：(1)在早期自动加工过程中, 汉语声调对词汇语义激活的作用; (2)在早期阶段, 汉语声调和语调加工的大脑激活模式; (3)在晚期阶段, 汉语声调和语调加工的大脑激活模式。对这些问题的考察将有助于澄清当前的激烈争论, 拓展以往基于非声调语言研究建立的口语加工理论的适用范围, 为完善言语认知加工的理论模型提供新的实验证据。     

Brain activity varies with modulation of dynamic pitch variance in sentence melody

Fourteen native speakers of German heard normal sentences, sentences which were either lacking dynamic pitch variation (flattened speech), or comprised of intonation contour exclusively (degraded speech). Participants were to listen carefully to the sentences and to perform a rehearsal task. Passive listening to flattened speech compared to normal speech produced strong brain responses in right cortical areas, particularly in the posterior superior temporal gyrus (pSTG). Passive listening to degraded speech compared to either normal or flattened speech particularly involved fronto-opercular and subcortical (Putamen, Caudate Nucleus) regions bilaterally. Additionally the Rolandic operculum (premotor cortex) in the right hemisphere subserved processing of neat sentence intonation. As a function of explicit rehearsing sentence intonation we found several activation foci in the left inferior frontal gyrus (Broca's area), the left inferior precentral sulcus, and the left Rolandic fissure. The data allow several suggestions: First, both flattened and degraded speech evoked differential brain responses in the pSTG, particularly in the planum temporale (PT) bilaterally indicating that this region mediates integration of slowly and rapidly changing acoustic cues during comprehension of spoken language. Second, the bilateral circuit active whilst participants receive degraded speech reflects general effort allocation. Third, the differential finding for passive perception and explicit rehearsal of intonation contour suggests a right fronto-lateral network for processing and a left fronto-lateral network for producing prosodic information. Finally, it appears that brain areas which subserve speech (frontal operculum) and premotor functions (Rolandic operculum) coincidently support the processing of intonation contour in spoken sentence comprehension.     

Effects of diet on early stage cortical perception and discrimination of syllables differing in voice-onset time: a longitudinal ERP study in 3 and 6 month old infants

The influence of diet on cortical processing of syllables was examined at 3 and 6 months in 239 infants who were breastfed or fed milk or soy-based formula. Event-related potentials to syllables differing in voice-onset-time were recorded from placements overlying brain areas specialized for language processing. P1 component amplitude and latency measures indicated that at both ages infants in all groups could extract and discriminate categorical information from syllables. Between-syllable amplitude differences—present across groups—were generally greater for SF infants. Responses peaked earlier over left hemisphere speech-perception than speech-production areas. Encoding was faster in BF than formula-fed infants. The results show that in preverbal infants: (1) discrimination of phonetic information occurs in early stages of cortical processing; (2) areas overlying brain regions of speech perception are activated earlier than those involved in speech production; and (3) these processes are differentially modulated by infant diet and environmental factors.     

Hemispheric differences in the effects of context on vowel perception

Listeners perceive speech sounds relative to context. Contextual influences might differ over hemispheres if different types of auditory processing are lateralized. Hemispheric differences in contextual influences on vowel perception were investigated by presenting speech targets and both speech and non-speech contexts to listeners’ right or left ears (contexts and targets either to the same or to opposite ears). Listeners performed a discrimination task. Vowel perception was influenced by acoustic properties of the context signals. The strength of this influence depended on laterality of target presentation, and on the speech/non-speech status of the context signal. We conclude that contrastive contextual influences on vowel perception are stronger when targets are processed predominately by the right hemisphere. In the left hemisphere, contrastive effects are smaller and largely restricted to speech contexts.     

An interactive Hebbian account of lexically guided tuning of speech perception

We describe an account of lexically guided tuning of speech perception based on interactive processing and Hebbian learning. Interactive feedback provides lexical information to prelexical levels, and Hebbian learning uses that information to retune the mapping from auditory input to prelexical representations of speech. Simulations of an extension of the TRACE model of speech perception are presented that demonstrate the efficacy of this mechanism. Further simulations show that acoustic similarity can account for the patterns of speaker generalization. This account addresses the role of lexical information in guiding both perception and learning with a single set of principles of information propagation.     

Do temporal processes underlie left hemisphere dominance in speech perception?

It is not unusual to find it stated as a fact that the left hemisphere is specialized for the processing of rapid, or temporal aspects of sound, and that the dominance of the left hemisphere in the perception of speech can be a consequence of this specialization. In this review we explore the history of this claim and assess the weight of this assumption. We will demonstrate that instead of a supposed sensitivity of the left temporal lobe for the acoustic properties of speech, it is the right temporal lobe which shows a marked preference for certain properties of sounds, for example longer durations, or variations in pitch. We finish by outlining some alternative factors that contribute to the left lateralization of speech perception.     

Functional brain activation differences in stuttering identified with a rapid fMRI sequence

The purpose of this study was to investigate whether brain activity related to the presence of stuttering can be identified with rapid functional MRI (fMRI) sequences that involved overt and covert speech processing tasks. The long-term goal is to develop sensitive fMRI approaches with developmentally appropriate tasks to identify deviant speech motor and auditory brain activity in children who stutter closer to the age at which recovery from stuttering is documented. Rapid sequences may be preferred for individuals or populations who do not tolerate long scanning sessions. In this report, we document the application of a picture naming and phoneme monitoring task in 3 min fMRI sequences with adults who stutter (AWS). If relevant brain differences are found in AWS with these approaches that conform to previous reports, then these approaches can be extended to younger populations. Pairwise contrasts of brain BOLD activity between AWS and normally fluent adults indicated the AWS showed higher BOLD activity in the right inferior frontal gyrus (IFG), right temporal lobe and sensorimotor cortices during picture naming and higher activity in the right IFG during phoneme monitoring. The right lateralized pattern of BOLD activity together with higher activity in sensorimotor cortices is consistent with previous reports, which indicates rapid fMRI sequences can be considered for investigating stuttering in younger participants.Educational objectives: The reader will learn about and be able to describe the: (1) use of functional MRI to study persistent developmental stuttering; (2) differences in brain activation between persons who stutter and normally fluent speakers; and (3) potential benefit of time efficient fMRI sequences combined with a range of speech processing tasks for investigating stuttering in younger populations.