Horn David L, Won Jong Ho, Rubinstein Jay T, Werner Lynne A
1Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology-Head and Neck Surgery, University of Washington, Seattle, Washington, USA; 2Division of Otolaryngology, Seattle Children's Hospital, Seattle, Wahington, USA; and 3Department of Speech and Hearing Sciences, University of Washington, Seattle, Washington.
Ear Hear. 2017 Mar/Apr;38(2):212-222. doi: 10.1097/AUD.0000000000000373.
Spectral resolution is a correlate of open-set speech understanding in postlingually deaf adults and prelingually deaf children who use cochlear implants (CIs). To apply measures of spectral resolution to assess device efficacy in younger CI users, it is necessary to understand how spectral resolution develops in normal-hearing children. In this study, spectral ripple discrimination (SRD) was used to measure listeners' sensitivity to a shift in phase of the spectral envelope of a broadband noise. Both resolution of peak to peak location (frequency resolution) and peak to trough intensity (across-channel intensity resolution) are required for SRD.
SRD was measured as the highest ripple density (in ripples per octave) for which a listener could discriminate a 90° shift in phase of the sinusoidally-modulated amplitude spectrum. A 2 × 3 between-subjects design was used to assess the effects of age (7-month-old infants versus adults) and ripple peak/trough "depth" (10, 13, and 20 dB) on SRD in normal-hearing listeners (experiment 1). In experiment 2, SRD thresholds in the same age groups were compared using a task in which ripple starting phases were randomized across trials to obscure within-channel intensity cues. In experiment 3, the randomized starting phase method was used to measure SRD as a function of age (3-month-old infants, 7-month-old infants, and young adults) and ripple depth (10 and 20 dB in repeated measures design).
In experiment 1, there was a significant interaction between age and ripple depth. The infant SRDs were significantly poorer than the adult SRDs at 10 and 13 dB ripple depths but adult-like at 20 dB depth. This result is consistent with immature across-channel intensity resolution. In contrast, the trajectory of SRD as a function of depth was steeper for infants than adults suggesting that frequency resolution was better in infants than adults. However, in experiment 2 infant performance was significantly poorer than adults at 20 dB depth suggesting that variability of infants' use of within-channel intensity cues, rather than better frequency resolution, explained the results of experiment 1. In experiment 3, age effects were seen with both groups of infants showing poorer SRD than adults but, unlike experiment 1, no significant interaction between age and depth was seen.
Measurement of SRD thresholds in individual 3 to 7-month-old infants is feasible. Performance of normal-hearing infants on SRD may be limited by across-channel intensity resolution despite mature frequency resolution. These findings have significant implications for design and stimulus choice for applying SRD for testing infants with CIs. The high degree of variability in infant SRD can be somewhat reduced by obscuring within-channel cues.
频谱分辨率与使用人工耳蜗（CI）的语后聋成年人及语前聋儿童的开放式言语理解能力相关。为了将频谱分辨率测量方法应用于评估较年幼CI使用者的设备效能，有必要了解正常听力儿童的频谱分辨率是如何发展的。在本研究中，频谱纹波辨别（SRD）被用于测量听众对宽带噪声频谱包络相位偏移的敏感度。SRD既需要峰到峰位置的分辨率（频率分辨率），也需要峰到谷强度的分辨率（跨通道强度分辨率）。
SRD被测量为听众能够辨别正弦调制幅度谱90°相位偏移的最高纹波密度（每倍频程的纹波数）。采用2×3被试间设计来评估年龄（7个月大的婴儿与成年人）和纹波峰/谷“深度”（10、13和20分贝）对正常听力听众SRD的影响（实验1）。在实验2中，使用一种任务比较相同年龄组的SRD阈值，该任务中纹波起始相位在各次试验中随机化，以模糊通道内强度线索。在实验3中，采用随机起始相位方法测量SRD作为年龄（3个月大的婴儿、7个月大的婴儿和年轻成年人）和纹波深度（重复测量设计中的10和20分贝）的函数。
在实验1中，年龄和纹波深度之间存在显著交互作用。在10分贝和13分贝纹波深度时，婴儿的SRD明显比成年人差，但在20分贝深度时与成年人相似。这一结果与跨通道强度分辨率不成熟一致。相比之下，婴儿的SRD随深度变化的轨迹比成年人更陡峭，表明婴儿的频率分辨率比成年人更好。然而，在实验2中，在20分贝深度时婴儿的表现明显比成年人差，这表明婴儿对通道内强度线索的利用差异，而非更好的频率分辨率，解释了实验1的结果。在实验3中，两组婴儿都表现出比成年人更差的SRD，但与实验1不同的是，未观察到年龄和深度之间的显著交互作用。
测量3至7个月大个体婴儿的SRD阈值是可行的。尽管频率分辨率已成熟，但正常听力婴儿在SRD上的表现可能受跨通道强度分辨率的限制。这些发现对将SRD应用于测试CI婴儿的设计和刺激选择具有重要意义。通过模糊通道内线索，婴儿SRD的高度变异性可有所降低。
