Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins Hospital, Baltimore, MD, USA.
Hear Res. 2011 Oct;280(1-2):192-200. doi: 10.1016/j.heares.2011.05.017. Epub 2011 May 31.
Cochlear implant (CI) users demonstrate severe limitations in perceiving musical timbre, a psychoacoustic feature of sound responsible for 'tone color' and one's ability to identify a musical instrument. The reasons for this limitation remain poorly understood. In this study, we sought to examine the relative contributions of temporal envelope and fine structure for timbre judgments, in light of the fact that speech processing strategies employed by CI systems typically employ envelope extraction algorithms. We synthesized "instrumental chimeras" that systematically combined variable amounts of envelope and fine structure in 25% increments from two different source instruments with either sustained or percussive envelopes. CI users and normal hearing (NH) subjects were presented with 150 chimeras and asked to determine which instrument the chimera more closely resembled in a single-interval two-alternative forced choice task. By combining instruments with similar and dissimilar envelopes, we controlled the valence of envelope for timbre identification and compensated for envelope reconstruction from fine structure information. Our results show that NH subjects utilize envelope and fine structure interchangeably, whereas CI subjects demonstrate overwhelming reliance on temporal envelope. When chimeras were created from dissimilar envelope instrument pairs, NH subjects utilized a combination of envelope (p = 0.008) and fine structure information (p = 0.009) to make timbre judgments. In contrast, CI users utilized envelope information almost exclusively to make timbre judgments (p < 0.001) and ignored fine structure information (p = 0.908). Interestingly, when the value of envelope as a cue was reduced, both NH subjects and CI users utilized fine structure information to make timbre judgments (p < 0.001), although the effect was quite weak in CI users. Our findings confirm that impairments in fine structure processing underlie poor perception of musical timbre in CI users.
人工耳蜗（CI）使用者在感知音乐音色方面存在严重限制，音色是声音的一种心理声学特征，负责“音色调”和识别乐器的能力。造成这种限制的原因仍知之甚少。在这项研究中，我们试图根据以下事实来检验时间包络和精细结构对音色判断的相对贡献：CI 系统所采用的语音处理策略通常采用包络提取算法。我们合成了“乐器嵌合体”，这些嵌合体系统地结合了来自两个不同源乐器的可变量的包络和精细结构，增量为 25%，具有持续或打击的包络。CI 用户和正常听力（NH）受试者被呈现 150 个嵌合体，并要求他们在单次间隔二选一强制选择任务中确定嵌合体更接近哪种乐器。通过结合具有相似和不同包络的乐器，我们控制了用于音色识别的包络的有效性，并从精细结构信息中补偿了包络的重建。我们的结果表明，NH 受试者可以互换使用包络和精细结构，而 CI 受试者则表现出对时间包络的过度依赖。当嵌合体由具有不同包络的乐器对创建时，NH 受试者利用包络（p = 0.008）和精细结构信息（p = 0.009）来进行音色判断。相比之下，CI 用户几乎完全利用包络信息来进行音色判断（p < 0.001），而忽略了精细结构信息（p = 0.908）。有趣的是，当包络作为提示的价值降低时，NH 受试者和 CI 用户都利用精细结构信息来进行音色判断（p < 0.001），尽管在 CI 用户中效果相当微弱。我们的研究结果证实，CI 用户对精细结构处理的损害是其对音乐音色感知能力差的原因。
