Cognitive Neuroimaging Unit, Institut National de la Santé et de la Recherche Médicale, F91191 Gif-sur-Yvette, France.
J Neurosci. 2012 Jun 27;32(26):9089-102. doi: 10.1523/JNEUROSCI.5685-11.2012.
Humans can understand spoken or written sentences presented at extremely fast rates of ∼400 wpm, far exceeding the normal speech rate (∼150 wpm). How does the brain cope with speeded language? And what processing bottlenecks eventually make language incomprehensible above a certain presentation rate? We used time-resolved fMRI to probe the brain responses to spoken and written sentences presented at five compression rates, ranging from intelligible (60-100% of the natural duration) to challenging (40%) and unintelligible (20%). The results show that cortical areas differ sharply in their activation speed and amplitude. In modality-specific sensory areas, activation varies linearly with stimulus duration. However, a large modality-independent left-hemispheric language network, including the inferior frontal gyrus (pars orbitalis and triangularis) and the superior temporal sulcus, shows a remarkably time-invariant response, followed by a sudden collapse for unintelligible stimuli. Finally, linear and nonlinear responses, reflecting a greater effort as compression increases, are seen at various prefrontal and parietal sites. We show that these profiles fit with a simple model according to which the higher stages of language processing operate at a fixed speed and thus impose a temporal bottleneck on sentence comprehension. At presentation rates faster than this internal processing speed, incoming words must be buffered, and intelligibility vanishes when buffer storage and retrieval operations are saturated. Based on their temporal and amplitude profiles, buffer regions can be identified with the left inferior frontal/anterior insula, precentral cortex, and mesial frontal cortex.
人类可以理解以非常快的速度（约 400 wpm）呈现的口语或书面句子，远远超过正常的语速（约 150 wpm）。大脑如何应对快速的语言？以及在什么处理瓶颈最终使语言在一定的呈现速度以上变得不可理解？我们使用时间分辨 fMRI 来探测大脑对以五种压缩率呈现的口语和书面句子的反应，压缩率范围从可理解（60-100%的自然持续时间）到具有挑战性（40%）和不可理解（20%）。结果表明，皮质区域在激活速度和幅度上有很大的差异。在模态特异性感觉区域，激活随刺激持续时间线性变化。然而，一个大型的模态独立的左半球语言网络，包括下额叶（眶部和三角部）和颞上回，表现出明显的时间不变的反应，然后对于不可理解的刺激突然崩溃。最后，在各种前额叶和顶叶部位可以看到反映随着压缩增加而增加的更大努力的线性和非线性反应。我们表明，这些轮廓与一个简单的模型相符，根据该模型，语言处理的较高阶段以固定的速度运行，从而对句子理解施加了时间瓶颈。在比内部处理速度更快的呈现速度下，输入的单词必须被缓冲，并且当缓冲区存储和检索操作饱和时，可理解性就会消失。根据它们的时间和幅度轮廓，可以将缓冲区区域识别为左侧下额叶/前岛叶、中央前回和内侧额回。
