Backus Bradford C, Guinan John J
Speech and Hearing Bioscience and Technology, Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA 02139, USA.
J Assoc Res Otolaryngol. 2007 Dec;8(4):484-96. doi: 10.1007/s10162-007-0100-0. Epub 2007 Oct 12.
A clinical test for the strength of the medial olivocochlear reflex (MOCR) might be valuable as a predictor of individuals at risk for acoustic trauma or for explaining why some people have trouble understanding speech in noise. A first step in developing a clinical test for MOCR strength is to determine the range and variation of MOCR strength in a research setting. A measure of MOCR strength near 1 kHz was made across a normal-hearing population (N = 25) by monitoring stimulus-frequency otoacoustic emissions (SFOAEs) while activating the MOCR with 60 dB SPL wideband contralateral noise. Statistically significant MOCR effects were measured in all 25 subjects; but not all SFOAE frequencies tested produced significant effects within the time allotted. To get a metric of MOCR strength, MOCR-induced changes in SFOAEs were normalized by the SFOAE amplitude obtained by two-tone suppression. We found this "normalized MOCR effect" varied across frequency and time within the same subject, sometimes with significant differences between measurements made as little as 40 Hz apart or as little as a few minutes apart. Averaging several single-frequency measures spanning 200 Hz in each subject reduced the frequency- and time-dependent variations enough to produce correlated measures indicative of the true MOCR strength near 1 kHz for each subject. The distribution of MOCR strengths, in terms of SFOAE suppression near 1 kHz, across our normal-hearing subject pool was reasonably approximated by a normal distribution with mean suppression of approximately 35% and standard deviation of approximately 12%. The range of MOCR strengths spanned a factor of 4, suggesting that whatever function the MOCR plays in hearing (e.g., enhancing signal detection in noise, reducing acoustic trauma), different people will have corresponding differences in their abilities to perform that function.
作为一种预测有遭受声损伤风险个体的指标,或者用于解释为何有些人在噪声环境中理解言语存在困难,检测内侧橄榄耳蜗反射(MOCR)强度的临床测试可能具有重要价值。开展MOCR强度临床测试的第一步是在研究环境中确定MOCR强度的范围和变化情况。通过在使用60 dB SPL宽带对侧噪声激活MOCR时监测刺激频率耳声发射(SFOAE),对25名听力正常的受试者测量了接近1 kHz频率处的MOCR强度。在所有25名受试者中均测量到了具有统计学意义的MOCR效应;但并非所有测试的SFOAE频率在规定时间内都产生了显著效应。为了获得MOCR强度的指标,将MOCR引起的SFOAE变化通过双音抑制获得的SFOAE幅度进行归一化处理。我们发现,同一受试者的这种“归一化MOCR效应”在频率和时间上会有所变化,有时相隔仅40 Hz或相隔仅几分钟的测量之间就存在显著差异。对每个受试者平均几个跨度为200 Hz的单频测量值,可充分减少频率和时间依赖性变化,从而得出与每个受试者接近1 kHz处的真实MOCR强度相关的测量值。在我们的听力正常受试者群体中,以接近1 kHz处的SFOAE抑制来衡量的MOCR强度分布合理地近似于正态分布,平均抑制约为35%,标准差约为12%。MOCR强度范围跨越了4倍,这表明无论MOCR在听力中发挥何种作用(例如,增强噪声中的信号检测、减少声损伤),不同的人在执行该功能的能力上都会有相应差异。