MRC Cognition and Brain Sciences Unit, 15 Chaucer Road, Cambridge, CB2 7EF, UK.
J Cogn Neurosci. 2011 Dec;23(12):3914-32. doi: 10.1162/jocn_a_00084. Epub 2011 Jul 11.
When speech is degraded, word report is higher for semantically coherent sentences (e.g., her new skirt was made of denim) than for anomalous sentences (e.g., her good slope was done in carrot). Such increased intelligibility is often described as resulting from "top-down" processes, reflecting an assumption that higher-level (semantic) neural processes support lower-level (perceptual) mechanisms. We used time-resolved sparse fMRI to test for top-down neural mechanisms, measuring activity while participants heard coherent and anomalous sentences presented in speech envelope/spectrum noise at varying signal-to-noise ratios (SNR). The timing of BOLD responses to more intelligible speech provides evidence of hierarchical organization, with earlier responses in peri-auditory regions of the posterior superior temporal gyrus than in more distant temporal and frontal regions. Despite Sentence content × SNR interactions in the superior temporal gyrus, prefrontal regions respond after auditory/perceptual regions. Although we cannot rule out top-down effects, this pattern is more compatible with a purely feedforward or bottom-up account, in which the results of lower-level perceptual processing are passed to inferior frontal regions. Behavioral and neural evidence that sentence content influences perception of degraded speech does not necessarily imply "top-down" neural processes.
当语音质量下降时，语义连贯的句子（例如，她的新裙子是用粗斜纹棉布做的）比异常句子（例如，她的好斜坡是用胡萝卜做的）的单词报告率更高。这种可懂度的提高通常被描述为“自上而下”过程的结果，反映了一种假设，即更高层次（语义）的神经过程支持更低层次（感知）的机制。我们使用时间分辨稀疏 fMRI 来测试自上而下的神经机制，在不同信噪比 (SNR) 下，通过语音包络/频谱噪声呈现连贯和异常句子，测量参与者的大脑活动。对更可懂语音的 BOLD 反应的时间提供了层次组织的证据，与更遥远的颞区和额区相比，后上颞叶的听觉/感知区域的反应更早。尽管在颞上回中存在句子内容×SNR 相互作用，但前额叶区域在听觉/感知区域之后做出反应。尽管我们不能排除自上而下的影响，但这种模式更符合纯粹的前馈或自下而上的解释，其中较低层次感知处理的结果传递到下额叶区域。言语内容影响感知退化语音的行为和神经证据并不一定意味着“自上而下”的神经过程。
