MRC Institute of Hearing Research, Nottingham, NG7 2RD, UK.
Cereb Cortex. 2012 Apr;22(4):745-53. doi: 10.1093/cercor/bhr065. Epub 2011 Jun 27.
Human neuroimaging studies have identified a region of auditory cortex, lateral Heschl's gyrus (HG), that shows a greater response to iterated ripple noise (IRN) than to a Gaussian noise control. Based in part on results using IRN as a pitch-evoking stimulus, it has been argued that lateral HG is a general "pitch center." However, IRN contains slowly varying spectrotemporal modulations, unrelated to pitch, that are not found in the control stimulus. Hence, it is possible that the cortical response to IRN is driven in part by these modulations. The current study reports the first attempt to control for these modulations. This was achieved using a novel type of stimulus that was generated by processing IRN to remove the fine temporal structure (and thus the pitch) but leave the slowly varying modulations. This "no-pitch IRN" stimulus is referred to as IRNo. Results showed a widespread response to the spectrotemporal modulations across auditory cortex. When IRN was contrasted with IRNo rather than with Gaussian noise, the apparent effect of pitch was no longer statistically significant. Our findings raise the possibility that a cortical response unrelated to pitch could previously have been errantly attributed to pitch coding.
人类神经影像学研究已经确定了听觉皮层的一个区域，即外侧 Heschl 回（HG），该区域对迭代波纹噪声（IRN）的反应比对高斯噪声控制的反应更大。部分基于使用 IRN 作为音高诱发刺激的结果，有人认为外侧 HG 是一个通用的“音高中心”。然而，IRN 包含与音高无关的缓慢变化的频谱时调制，而在对照刺激中则没有。因此，IRN 引起的皮质反应可能部分是由这些调制引起的。本研究报告了首次尝试控制这些调制的尝试。这是通过使用一种新型刺激来实现的，该刺激通过处理 IRN 来去除精细的时间结构（从而去除音高），但保留缓慢变化的调制。这种“无音高 IRN”刺激称为 IRNo。结果显示，听觉皮层对频谱时间调制有广泛的反应。当将 IRN 与 IRNo 进行对比，而不是与高斯噪声进行对比时，音高的明显效果不再具有统计学意义。我们的发现提出了一种可能性，即以前可能错误地将与音高无关的皮质反应归因于音高编码。
