McNealy Kristin, Mazziotta John C, Dapretto Mirella
Ahmanson-Lovelace Brain Mapping Center, Semel Institute for Neuroscience and Human Behavior, Los Angeles, California 90095, USA.
J Neurosci. 2006 Jul 19;26(29):7629-39. doi: 10.1523/JNEUROSCI.5501-05.2006.
Word segmentation, detecting word boundaries in continuous speech, is a critical aspect of language learning. Previous research in infants and adults demonstrated that a stream of speech can be readily segmented based solely on the statistical and speech cues afforded by the input. Using functional magnetic resonance imaging (fMRI), the neural substrate of word segmentation was examined on-line as participants listened to three streams of concatenated syllables, containing either statistical regularities alone, statistical regularities and speech cues, or no cues. Despite the participants' inability to explicitly detect differences between the speech streams, neural activity differed significantly across conditions, with left-lateralized signal increases in temporal cortices observed only when participants listened to streams containing statistical regularities, particularly the stream containing speech cues. In a second fMRI study, designed to verify that word segmentation had implicitly taken place, participants listened to trisyllabic combinations that occurred with different frequencies in the streams of speech they just heard ("words," 45 times; "partwords," 15 times; "nonwords," once). Reliably greater activity in left inferior and middle frontal gyri was observed when comparing words with partwords and, to a lesser extent, when comparing partwords with nonwords. Activity in these regions, taken to index the implicit detection of word boundaries, was positively correlated with participants' rapid auditory processing skills. These findings provide a neural signature of on-line word segmentation in the mature brain and an initial model with which to study developmental changes in the neural architecture involved in processing speech cues during language learning.
词切分，即在连续语音中检测词边界，是语言学习的一个关键方面。先前针对婴儿和成人的研究表明，仅凭输入所提供的统计和语音线索，就能轻松地对语音流进行切分。使用功能磁共振成像（fMRI），在参与者收听由三个拼接音节组成的语音流时，对词切分的神经基础进行了在线检测，这些语音流分别只包含统计规律、统计规律和语音线索，或者不包含任何线索。尽管参与者无法明确检测出语音流之间的差异，但不同条件下的神经活动存在显著差异，只有当参与者收听包含统计规律的语音流，特别是包含语音线索的语音流时，才会在颞叶皮质观察到左侧信号增强。在第二项fMRI研究中，为了验证词切分是否已隐性发生，参与者收听了在他们刚刚听到的语音流中以不同频率出现的三音节组合（“单词”45次；“部分单词”15次；“非单词”1次）。在比较单词与部分单词时，以及在较小程度上比较部分单词与非单词时，观察到左下额叶和额中回的活动可靠地增强。这些区域的活动被视为词边界隐性检测的指标，与参与者的快速听觉处理技能呈正相关。这些发现提供了成熟大脑中在线词切分的神经特征，以及一个初步模型，可用于研究语言学习过程中处理语音线索所涉及的神经结构的发育变化。
