The Sensitive Period for Speech Perception

描述（由申请人提供）：儿童和青少年时期言语感知变化的可塑性，导致第二语言习得的敏感期。然而，这种变化的发育过程和潜在的认知和神经机制尚未得到充分的了解。本研究提出了一种假设，即母语感知的“巩固”是这种年龄限制学习的机制之一。我们的具体目标是：1)研究出生年龄对第二语言言语类别知觉专业知识的影响。我们将使用一套实验方法研究正在学习英语的日语为母语的成年人，包括：a)结合心理物理测量和敏感眼动追踪测量的视觉世界任务；b)研究语音分类功能解剖的fMRI“无任务”习惯化范式；c)匹配行为结果时间进程的EEG习惯化范式；d)评估感知和生产发展之间关系的生产任务。2)将上述方法应用于6-18岁母语为英语的儿童和青少年语音分类的发展。3)在目标1和目标2的数据中，探讨母语专业知识的出现与第二语言言语类别可塑性下降之间的关系。我们假设，敏感期可塑性的下降与知觉经验的增加有关。以同样的范式和刺激收集的数据，适用于以日语为母语的成年人、以英语为母语的儿童、青少年和成年人，将成为对这一假设进行有力检验的基础。这项研究将提供从童年到成年的典型语言感知发展过程的见解，为研究基本学习失败背后的认知和神经机制提供一个模型系统。规范数据、范式和机制见解可能最终有利于临床人群（即阅读障碍、语言障碍和学习障碍）的非典型发育研究。

DESCRIPTION (provided by applicant): Plasticity for speech perception changes during childhood and adolescence, resulting in a sensitive period for second-language acquisition. However, the developmental time-course and the underlying cognitive and neural mechanisms of this change are not adequately understood. The proposed research investigates the hypothesis that "entrenchment" of native language perception is one mechanism of such age-limited learning. Our specific aims are: 1) Examine the influence of age of arrival on perceptual expertise for second-language speech categories. We will study adult native speakers of Japanese who are learning English using a suite of experimental methods including: a) a visual world task that combines psychophysical measures and sensitive eye-tracking measures, b) a "task free" dishabituation paradigm for fMRI to study the functional anatomy of phonetic categorization and c) a dishabituation paradigm for EEG that matches the timecourse of the behavioral results and d) productions tasks to assess the relationship between perception and production development. 2) Examine the development of phonetic categorization in children and adolescents applying the methods developed above to native English speakers age 6-18. 3) Explore the relationship between the emergence of native-language expertise and the decline in plasticity for second-language speech categories in the data from Aims 1 and 2. We hypothesize that the decline in plasticity during the sensitive period is associated with increasing perceptual expertise. Data collected with the same paradigms and stimuli for adult native speakers of Japanese, native English speaking children, adolescents and adults will be the basis for a strong test of this hypothesis. This investigation will provide insights into the typical developmental timecourse of speech perception from childhood to adulthood, which provides a model system in which to study the cognitive and neural mechanisms behind a basic failure of learning. The normative data, paradigms, and mechanistic insights may ultimately benefit studies of atypical development in clinical populations (i.e. dyslexia, language impairments, and learning disabilities).