Neural Bases of Lexical Effects

描述(申请人提供)：本研究的目的是调查词汇效应在语音类别识别中的神经基础。这将通过在正常受试者中使用功能磁共振成像(FMRI)来完成，因为他们对语音标记做出语音判断，这些声音标记的语音歧义程度和词汇状态都不同。这项研究预计将阐明两个一般问题。第一，语音类别知觉的神经机制是什么；第二，词汇状态的自上而下效应对这些机制的影响有多大。实验将使用与事件相关的功能磁共振成像，它消除了阻止刺激的需要，以及稀疏采样扫描技术，允许在相对安静的情况下呈现声学标记。假设词汇状态对音素同一性判断的影响可以在语音加工流的知觉阶段看到，这支持了词汇加工的一个整合的连接主义模型，在该模型中，较高水平的加工直接影响较低水平的知觉。我们还假设，作为刺激不确定性和词汇状态的函数，左额叶上回、左额叶下回和前扣带回将出现不同的激活调制模式。由于自上而下效应，大脑区域显示了激活的调制，这一发现可能有助于揭示失语症患者在这些区域有损害的语言缺陷的本质。

DESCRIPTION (provided by applicant): The goal of this research is to investigate the neural basis of lexical effects on the identification of phonetic categories. This will be accomplished by using functional magnetic resonance imaging (fMRI) in normal subjects as they make phonetic judgments to acoustic tokens which vary in both their degree of phonetic ambiguity as well as their lexical status. This research is expected to elucidate two general issues. First, what are the neural mechanisms which underlie perception of phonetic categories, and second, to what extent do top-down effects of lexical status influence those mechanisms. Experiments will use event-related fMRI, which obviates the need to block stimuli, and a sparse-sampling scanning technique, which allows for the presentation of acoustic tokens in relative silence. It is hypothesized that effects of lexical status on judgments of phoneme identity can be seen at perceptual stages of the speech processing stream, supporting an integrative, connectionist model of lexical processing in which upper levels of processing directly influence perception at lower levels. It is also hypothesized that differential patterns of modulation of activation will emerge in the left superior temporal gyrus, the left inferior temporal gyrus and anterior cingulate as a function of both stimulus uncertainty and lexical status. A discovery of brain areas which show modulation of activation due to top-down effects may shed light on the nature of language deficits in aphasic patients who have lesions in these areas.