Allen Emily J, Burton Philip C, Olman Cheryl A, Oxenham Andrew J
Department of Psychology, University of Minnesota, Minneapolis, Minnesota 55455
Department of Psychology, University of Minnesota, Minneapolis, Minnesota 55455.
J Neurosci. 2017 Feb 1;37(5):1284-1293. doi: 10.1523/JNEUROSCI.2336-16.2016. Epub 2016 Dec 26.
Pitch and timbre are two primary dimensions of auditory perception, but how they are represented in the human brain remains a matter of contention. Some animal studies of auditory cortical processing have suggested modular processing, with different brain regions preferentially coding for pitch or timbre, whereas other studies have suggested a distributed code for different attributes across the same population of neurons. This study tested whether variations in pitch and timbre elicit activity in distinct regions of the human temporal lobes. Listeners were presented with sequences of sounds that varied in either fundamental frequency (eliciting changes in pitch) or spectral centroid (eliciting changes in brightness, an important attribute of timbre), with the degree of pitch or timbre variation in each sequence parametrically manipulated. The BOLD responses from auditory cortex increased with increasing sequence variance along each perceptual dimension. The spatial extent, region, and laterality of the cortical regions most responsive to variations in pitch or timbre at the univariate level of analysis were largely overlapping. However, patterns of activation in response to pitch or timbre variations were discriminable in most subjects at an individual level using multivoxel pattern analysis, suggesting a distributed coding of the two dimensions bilaterally in human auditory cortex.
Pitch and timbre are two crucial aspects of auditory perception. Pitch governs our perception of musical melodies and harmonies, and conveys both prosodic and (in tone languages) lexical information in speech. Brightness-an aspect of timbre or sound quality-allows us to distinguish different musical instruments and speech sounds. Frequency-mapping studies have revealed tonotopic organization in primary auditory cortex, but the use of pure tones or noise bands has precluded the possibility of dissociating pitch from brightness. Our results suggest a distributed code, with no clear anatomical distinctions between auditory cortical regions responsive to changes in either pitch or timbre, but also reveal a population code that can differentiate between changes in either dimension within the same cortical regions.
音高和音色是听觉感知的两个主要维度，但它们在人脑中如何呈现仍是一个有争议的问题。一些关于听觉皮层处理的动物研究表明存在模块化处理，不同的脑区优先编码音高或音色，而其他研究则表明在同一群神经元中对不同属性进行分布式编码。本研究测试了音高和音色的变化是否会在人类颞叶的不同区域引发活动。向受试者呈现声音序列，这些序列在基频（引发音高变化）或频谱质心（引发亮度变化，音色的一个重要属性）上有所不同，每个序列中音高或音色变化的程度进行参数化操作。听觉皮层的血氧水平依赖（BOLD）反应随着沿每个感知维度序列方差的增加而增加。在单变量分析水平上，对音高或音色变化最敏感的皮层区域的空间范围、区域和偏侧性在很大程度上是重叠的。然而，使用多体素模式分析在个体水平上，大多数受试者对音高或音色变化的激活模式是可区分的，这表明在人类听觉皮层中这两个维度是双侧分布式编码的。
音高和音色是听觉感知的两个关键方面。音高支配着我们对音乐旋律与和声的感知，并在语音中传达韵律和（在声调语言中）词汇信息。亮度——音色或音质的一个方面——使我们能够区分不同的乐器和语音。频率映射研究揭示了初级听觉皮层中的音调拓扑组织，但使用纯音或噪声带排除了区分音高和亮度的可能性。我们的结果表明存在一种分布式编码，在对音高或音色变化做出反应的听觉皮层区域之间没有明显的解剖学差异，但也揭示了一种群体编码，能够在同一皮层区域内区分任一维度的变化。
