正常听力青年人诱发性耳声发射测试

本文利用耳声发射分析仪ＣＥＬＥＳＴＡ５０３对２０名正常听力青年人进行了ＤＰＯＡＥ和ＴＥＯＡＥ测试，结果发现平均ＤＰＯＡＥ图中有两个反应高峰，分别位于１ｋＨｚ和６ｋＨｚ附近，两峰之间于３ｋＨｚ左右有一反应低谷。左右耳及性别差异对ＤＰＯＡＥ无显著性影响。ＤＰＯＡＥ的反应幅值随两个初始纯音强度的增加而升高，平均检测阈值在３０～４５ｄＢＳＰＬ之间。当初始音强度≤７０ｄＢＳＰＬ时，平均Ｉ／Ｏ函数曲线未见明显饱和现象。若采用不等强度的初始纯音（Ｌ１＝７０ｄＢＳＰＬ，Ｌ１－Ｌ２＝５ｄＢ）刺激，在中频部分（１．５～４ｋＨｚ）可获得较等强度初始纯音刺激时高的ＤＰＯＡＥ反应。由８０ｄＢｐｅＳＰＬ短声诱发的ＴＥＯＡＥ检出率为１００％，平均幅值４．１１±３．９９ｄＢＳＰＬ（ｘ±ｓ）。两种耳声发射之间有显著相关性。     

正常清醒豚鼠的畸变产物耳声发射特性

目的 研究正常清醒豚鼠的畸变产物耳声发射（ＤＰＯＡＥ）的特性。方法 采用ＣＥＬＥＳＴＡ ５０３型耳声发射分析仪对２６只正常清醒豚鼠（３５耳）进行ＤＰ图及ＤＰ输入／输出曲线（ＤＰ－Ｉ／Ｏ）的测试，随机选择１１只正常清醒豚鼠（２０耳）进行ＤＰＯＡＥ的重复测试，用ＳＰＳＳ１０．０对数据进行统计分析。结果 在ＤＰ图中，当初始音强度Ｌ１／Ｌ２为 ７０／６５ ｄＢ ＳＰＬ时，正常清醒豚鼠的 ＤＰＯＡＥ幅值随测试频率ｆ０从０．７５－８ｋＨｚ的增加而逐渐升高（２７．９０±１．９６－5０．６５±０．７１）。在 ＤＰ－Ｉ／Ｏ中，当ｆ０分别为４、６、８ ｋＨｚ时，正常清醒豚鼠的ＤＰＯＡＥ幅值随Ｌ１／Ｌ２从７０／６５以５ｄＢ－挡降至１５／１０ ｄＢ ＳＰＬ而呈线性下降（Ｐ＜０．０１），在Ｌ１／Ｌ２为５５／５０或６０／５５ ｄＢ ＳＰＬ处出现饱和或低谷，同一Ｉ／Ｏ曲线上Ｌ１／Ｌ２分别从７０／６５及５５／５０ ｄＢ ＳＰＬ递减至阈值的Ｉ／Ｏ斜率（分别记为ＫＴ及ＫＬ）均接近于１，且ＫＬ大于ＫＴ（Ｐ＜０．０１）。重复测试的ＤＰＯＡＥ幅值差异小（＜ １ｄＢ ＳＰＬ）且无统计学意义（Ｐ＞０．０５）。结论 正常清醒豚鼠ＤＰＯＡＥ测试充分表现了其捡出率高、反应幅值大     

对听力正常人几种耳声发射基本特性的研究

本文利用耳动态分析仪ＩＬＯ－９２对３５名听力正常人进行了ＤＰＯＡＥ、ＴＥＯＡＥ和ＳＯＡＥ检查,结果发现ＤＰＯＡＥ反应在２ｆ１－ｆ２处最大,其幅值随两个初始刺激音强度的增加而升高,检测阈值在２０～４０ｄＢＳＰＬ之间,而反应潜伏期则随刺激频率升高而缩短；平均ＤＰＯＡＥ图中有两个反应峰分别位于１．４ｋＨｚ和５．６ｋＨｚ附近。由８０±１ｄＢＳＰＬ短声诱发的ＴＥＯＡＥ检出率为１００％,平均幅值为１０．１０±３．９３ｄＢＳＰＬ（±ＳＤ）；另外,约有４９％的受试者具有ＳＯＡＥ反应,频率范围在０．５～６ｋＨｚ之间,幅值范围为—２８～６ｄＢＳＰＬ；对上述有关参量进行统计学分析,发现三种ＯＡＥｓ之间存在一定的相关性。     

短时纯音暴露对正常人畸变产物耳声发射幅值及频谱时间序列的影响

探讨在耳蜗功能早期轻微损害时畸变产物耳声发射（ＤＰＯＡＥ）幅值及频谱时间序列的特征,促进ＤＰＯＡＥ的临床应用。方法：用 １３０ｄＢ ＳＰＬ的 ４ ｋＨｚ纯音对 １５例听力正常人（３０耳）进行 ３ ｍｉｎ的短时暴露,造成听力暂时性阈移后,用ＩＬＯ－９０耳声发射仪记录、分析暂时性阈移（ＴＴＳ）时ＤＰＯＡＥ的幅值、时间序列的特征,并与纯音暴露前进行对比。结果：正常人经过短时纯音暴露后,０．５,１,２ ｋＨｚ纯音和宽带噪声的声反射阈升高,纯音暴露前后０．５、１、２ ｋＨｚ与ＢＢＮ之间的平均反射阈差值分别为（９．７８±６．９８）,（８．０４±５．５８）,（１３．０±５．５８） ｄＢ ＨＬ和（８．８２±６．２３）,（５．７５±４．４２）,（９．０５±２．２７）ｄＢ ＨＬ,声反射阈差值缩小。纯音暴露前后６ ｋＨｚＤＰＯＡＥ幅值分别为（６．００±３．４５）和（１．７２±１. ２３） ｄＢ ＳＰＬ,降低４．２８ ｄＢ ＳＰＬ,时间序列变异系数为（５．１８±１．６３）％,时间序列曲线稳定性降低,ＤＰＯＡＥ幅值与时间序列结合发现８０％的人ＤＰＯＡＥ处于异常范围。结论：ＤＰＯＡＥ的幅值与时间序列结合分析有诊断耳蜗功能早期轻微受损的临床价值。     

豚鼠畸变产物耳声发射正常值测试及其相互关系

为探讨豚鼠１，２，４、６ｋＨｚ的畸变产物耳声发射（ＤＰＯＡＥ）正常值，对１２只（１５耳）豚鼠ＤＰＯＡＥ进行了较系统的测试，并就其间的相互关系进行了分析。各频率的测出率均为１００％；２ｋＨｚ以上的幅值均在２５ｄＢ ＳＰＬ以上，１ｋＨｚ的幅值低于其它频率；２ｋＨｚ以上的反应阀值低于１ｋＨｚ；潜伏期随频率的增加有缩短的趋势；Ｉ／０函数曲线表明各频率的ＤＰＯＡＥ幅值随初始音的强度降低而减少，两者音存在着极     

不同类型及强度的对侧声刺激对畸变产物耳声发射的影响

目的 观察不同类型及强度的对侧声刺激对ＤＰＯＡＥ的影响。方法 以三种不同类型（白噪声，窄带噪声，纯音）及八种强度（阈上０－３５ｄＢ范围内，每档５ｄＢ）的对侧声刺激测试１２例正常人（２４耳）在有，无对侧声刺激出现时的ＤＰＯＡＥ幅值变化。结果（１）三种类型的对侧声刺激均能使ＤＰＯＡＥ幅值下降，白噪声抑制作用最大，窄带噪声次之，纯音抑制作用最小。（２）随对侧声刺激强度增加，抑制现象增加两垧显著相关。（     

初始音强度差对听力正常青年人畸变产物耳声发射的影响

目的 探讨初始音强度差对听务正常青年人畸变产物耳声发射（ＤＰＯＡＥ）幅值的影响,为临床应用ＤＰＯＡＥ提供最佳的刺激强度组合。方法 用ＩＨＳ Ｖｅｒｓｉｏｎ ３．２型耳声发射仪对听务正常青年人３９耳进行了ＤＰＯＡＥ测试,分别记录Ｌ１为７５,６５,５５ｄＢ ＳＰＬ,强度差Ｌ１－Ｌ２为０,５,１０,１５,ｄＢ ＳＰＬ时,不同Ｌ１－Ｌ２值对ＤＰＯＡＥ幅值的影响。     

短时纯音暴露对正常人畸变产物耳声发射幅值及频谱时间序 …

目的：探讨在耳蜗功能早期以微损害时畸变产物耳声发射（ＤＰＯＡＥ）幅值及频谱邓列的特征，促进ＤＰＯＡＥ的临床。方法：用１３０ｄＢＳＰＬ的４ｋＨｚ纯音对１５例听力正常人（３０耳）进行３ｍｉｎ的短时暴露，造成听力暂时性阈移后，用ＩＬＯ－９０耳声发射仪记录，分析暂时性阈移（ＴＴＳ）时ＤＰＯＡＥ的幅值，时间序列的特征，并与纯音暴露前进行对比。结果：正常人经过短时纯音暴露后，０．５，１．２ｋＨｚ纯音和宽带噪声     

短时纯音暴露对畸变产物耳声发射的影响

畸变产物耳声发射（ＤＰＯＡＥ）测试所采用的参数可以对测试结果有明显影响，为研究改变ＤＰＯＡＥ测试参数对反映耳蜗功能变化是否有影响，使１０只大白兔（１６耳）接触短时（３分钟）、中等强度（８２ｄＢ ＳＰＬ）的纯音暴露后发现，以等强原始音（Ｌ１＝Ｌ２）诱发的ＤＰＯＡＥ的幅度变化小于以差强原始音（Ｌ２＝Ｌ１－１２ｄＢ）诱发的ＤＰＯＡＥ（相差１０．１１ｄＢ），而其恢复过程也短于后者（相差１００．７１秒）。这     

豚鼠畸变产物微音器电位与畸变产物耳声的发射的相关？…

为探讨畸变产物微间电位（ＤＰＣＭ）是否畸变产物耳声发射（ＤＰＯＡＥ）引发，将豚鼠的ＤＰＯＡＥ和ＤＰＣＭ同时叠加，发现在较高强度的声刺激下（ｆ０＝１００６Ｈｚ，ｆ０＝２０１１Ｈｚ，ｆ０＝４０３３Ｈｚ），ＤＰＣＭ叠加结果与ＤＰＯＡＥ各峰有一一对应的关系，ＣＭ的２ｆ１－ｆ２峰相对值（与ｆ１峰比值）比ＤＰＯＡＥ的２ｆ－ｆ２要小得多。较低声强刺激时（ｆ０＝１００６Ｈｚ〈５０ｄＢ，ｆ０＝２０１１Ｈｚ〈６０ｄＢ     

Influence of contralateral acoustic stimulation on distortion-product and spontaneous otoacoustic emissions in the barn owl

The avian auditory papilla provides an interesting object on which to study efferent influences, because whereas a significant population of hair cells in birds is not afferently innervated, all hair cells are efferently innervated (Fischer, 1992, 1994a, b). Previous studies in mammals using contralateral sound to stimulate the efferent system demonstrated a general suppressive effect on spontaneous and click-evoked, as well as on distortion-product otoacoustic emissions (DPOAE). As little is known about the effects of contralateral stimulation on hearing in birds, we studied the effect of such stimuli (broadband noise, pure tones) on the amplitude of the DPOAE 2f(1)-f(2) and on spontaneous otoacoustic emissions (SOAE) in the barn owl, Tyto alba. For the DPOAE measurements, fixed primary-tone pairs [f(1)=8.875 kHz (ratio=1.2), f(1)=8.353 kHz (ratio=1.15) and f(1)=7.889 kHz (ratio=1.1)] were presented and the DPOAE measured in the presence and absence of continuous contralateral stimulation. The DPOAE often declined in amplitude but in some cases we observed DPOAE enhancement. The changes in amplitude were as large as 9 dB. The influence of the contralateral noise changed over time, however, and the effects of contralateral tones were frequency-dependent. SOAE were suppressed in amplitude and shifted in frequency by contralateral broadband noise. Control measurements in animals after middle-ear muscle resection showed that these phenomena were not attributable to the acoustic middle-ear reflex. The finding of DPOAE enhancement is interesting, because a type of efferent fiber that suppressed its discharge rate during stimulation has been described in birds (Kaiser and Manley, 1994).     

Rapid adaptation of the 2f1-f2 DPOAE in humans: binaural and contralateral stimulation effects

The present data were collected in humans to characterize the effects of monaural and binaural stimulation and contralateral noise on the 2f1-f2 distortion-product otoacoustic emission (DPOAE) adaptation response. DPOAE levels (f2/f1=1.21, L1=70 dB SPL, L2=65 dB SPL) were measured in both ears for a range of f2 frequencies (1.2 to 10.0 kHz). The f2 frequency producing the largest amplitude DPOAE was used for further testing employing three different stimulus conditions: the primary tones were presented to only one ear for 4 s; the two tones were presented simultaneously in both ears; and, contralateral broadband noise (60 dB SPL) was presented for 5 s, beginning 4 s after the onset of the monaural primaries in the test ear. Acoustic reflex thresholds were measured to verify that the middle-ear muscles played no systematic role in the measured DPOAE reductions. Estimates of monaural rapid adaptation levels and time constants agreed well with previous human findings. The magnitude of the rapid adaptation under binaural stimulation, as compared with monaural primaries, was 25% greater on average, though adaptation time constants were comparable. With added contralateral noise, the average DPOAE suppression was 1.1 dB (0.3-2.7 dB). The magnitude of the monaural adaptation and the effects of binaural and contralateral stimulation, however, were smaller than those measured previously in experimental animals, though the time constants were in good agreement.     

Effect of ipsilateral and contralateral low-frequency narrow-band noise on temporary threshold shift in humans

OBJECTIVE: To evaluate the effect of ipsilateral and contralateral low-frequency (250 Hz) narrow-band noise (NBN) on the temporary threshold shift (TTS) induced by a 2 kHz tone in young normally hearing subjects with a functioning auditory efferent system. MATERIAL AND METHODS: Sixteen young volunteers served as subjects. All the subjects were young (20-30 years), disease-free and had a medical history negative for otological disease, noise exposure and use of ototoxic drugs. They had normal hearing [thresholds of 125-8,000 Hz below 20 dB hearing level (HL)], transient-evoked otoacoustic emissions and contralateral suppression. The subjects were randomly assigned to one of three different groups. Subjects in Group A (n = 5) were exposed to a 90 dB HL 2 kHz pure tone for 10 min. Subjects in Group B (n = 6) were exposed to a 90 dB HL 2 kHz pure tone and an ipsilateral 45 dB HL 250 Hz NBN for 10 min. Subjects in Group C (n = 5) were exposed to a 90 dB HL 2 kHz pure tone and a contralateral 45 dB HL 250 Hz NBN for 10 min. The right ear served as the test ear. The TTS 2 min after the end of the exposure (TTS2) was measured in all subjects at 2, 3 and 4 kHz. RESULTS: TTS, in Group A was significantly higher at 3 kHz (p = 0.011) and at 4 kHz (p = 0.003) than TTS2 in Group B. At 4 kHz, TTS2 in Group C was significantly higher (p = 0.013) than TTS2 in Group B. Although TTS2 in Group C was lower than TTS2 in Group A, this difference was not significant. The presence of an ipsilateral low-frequency NBN significantly reduced TTS2 induced by a 90 dB HL 2 kHz tone. A contralateral low-frequency NBN reduced TTS2 in this group of subjects; however, the reduction was not significant. CONCLUSION: The results of this study show that an ipsilateral low-intensity, low-frequency (250 Hz) NBN can give protection from a TTS induced by a 2 kHz tone. Contralateral low-frequency NBN did not induce any protective effect.     

Changes in distortion product otoacoustic emissions during prolonged noise exposure

The aim of this study was to evaluate the reduction in 2f₁−f₂ distortion product otoacoustic emission (DPOAE) amplitude resulting from prolonged noise exposures. A group of five chinchillas was exposed continuously to an octave-band noise centered at 4.0 kHz for a total of 42 days, 6 days at each of seven exposure levels. Exposure level increased in 8-dB steps from 48 to 96 dB SPL. DPOAE input-output (I/O) functions were measured at octave intervals over a range of primary tone f₂ frequencies between 1.2 and 9.6 kHz. Measurements were obtained (1) pre-exposure, (2) during days 3–6 of each 6-day exposure, and (3) 4 weeks after the final exposure. Continuous noise exposure caused a reduction in DPOAE amplitude that was greatest at f₂ frequencies within and above (3.4–6.8 kHz) the octave-band noise exposure. For these f₂ frequencies, DPOAE amplitudes decreased as exposure level increased up to approximately 72–80 dB SPL; higher exposure levels failed to cause any further reduction in DPOAE amplitude. The noise level at which DPOAE amplitude began to decrease was approximately 50 dB SPL. Above this critical level, DPOAE amplitude decreased 1.3 dB for every dB increase in noise level up to approximately 75 dB SPL.     

Assessment of the medial olivocochlear efferent system in children. pure tone 1.0 kHz and 2.0 kHz suppressive effects on transient evoked otoacoustic emission

The role of medial efferent system in regulating outer hair cell function has been studied by many investigators. Usually narrow band noise or white noise as contralateral stimulation (CS) suppressors have been used and changes in OAE amplitudes estimated. Thirty children aged 6-15 years (mean 12.5 +/- 4.7), without any changes in tonal and impedance audiometry and with negative history regarding otiatric diseases were examined. Transient evoked otoacoustic emissions (TEOAE) were recorded using ILO 92 Otodynamics Analyser. CS was performed using 1.0 kHz and 2.0 kHz continuous pure tones of 30 dB SL or 50 dB SL. Effects of CS on TEOAE evoked by click of 80, 70 and 60 dB SPL were investigated. TEOAE analysis included assessment of TEOAE amplitude of half octave frequency bandwidth (HOFBW-1.0; HOFBW-1.5; HOFBW-2.0; HOFBW-3.0 and HOFBW-4.0 kHz) and 0.8 kHz frequency bandwidth (0.8-FBW) amplitudes centred at 1.0; 2.0; 3.0; 4.0 and 5.0 kHz. TEOAE amplitude recorded for stimuli 80, 70 and 60 dB SPL without CS decreased: mean values respectively 6.1 +/- 4.2; 5.4 +/- 4.5 and 3.3 dB SPL +/- 4.3. CS effect on TEOAE was observed for all CS options, however, larger suppressive effect was recorded on TEOAE elicited by 70 dB SPL stimulus using 1 kHz/50 dB SL tone as a suppressor and on TEOAE elicited by 60 dB SPL stimulus using 2 kHz/50 dB SL tone as a suppressor. HOFBW and 0.8-FBW analyses showed the association between the frequency/intensity of the suppressors and decreasing of amplitudes of adequate frequency bands. It is concluded that the described method of investigating of the medial olivocochlear efferent system seems to be sensitive and confirms frequency-dependent suppressive effect on OAE.     

耳声发射对侧抑制效应的频率特异性研究

目的　观察耳声发射对侧抑制效应是否有频率特异性。方法　分别测试７ 例正常人（１４耳） 畸变产物耳声发射（ＤＰＯＡＥ） 和２ 例正常人（２ 耳） 自发性耳声发射（ＳＯＡＥ） 的对侧抑制效应,对侧声刺激为窄带噪声（ＮＢＮ） 。结果　当对侧ＮＢＮ 中心频率等于ＤＰＯＡＥ 的初始音ｆ２ 频率和ＳＯＡＥ 频率时,ＤＰＯＡＥ 和ＳＯＡＥ 发生最大抑制。结论　本实验进一步表明耳声发射对侧抑制效应有频率特异性,提示内侧橄榄耳蜗系统和耳蜗外毛细胞参与了耳蜗频率特性的主动调谐过程,提高了耳蜗频率分辨率。文中讨论了频率特异性的发生机理     

自发性耳声发射与耳蜗传出调控的关系探讨

OBJECTIVE: To study the relationship between spontaneous otoacoustic emissions(SOAE) and efferent control of cochlea and their clinical significance. METHODS: SOAE, transient evoked otoacoustic emissions (TEOAE), distortion product otoacoustic emissions (DPOAE) and contralateral white noise (60 dB SPL) suppression of TEOAE and DPOAE experiments were conducted in 312 ears of 95 patients with retrocochlear impairment and/or MOCS dysfunction and 64 normal young adults. RESULTS: MOCS dysfunction was shown in 126 ears of 65 patients (130 ears) with auditory neuropathy, 2 ears of 2 patients with unilateral acoustic neuroma, 4 ears of 2 patients with hyperacusis, 14 ears of 26 patients(48 ears) with normal hearing level in unilateral or bilateral tinnitus. Stronger EOAE could be recorded in total 146 ears with MOCS dysfunction at any pure tone hearing level. SOAE could be recorded in 126 of 146 ears (86.3%) with MOCS dysfunction and 44 of 128 ears (34.3%) with normal hearing. SOAE of ears with MOCS dysfunction was mainly at frequencies from 0.693 to 3.055 kHz and SOAE of normal ears was at frequencies from 1.135 to 2.746 kHz. Average value of maximum amplitude of SOAE spectrum (-3.4 +/- 6.4) dB SPL was significantly greater than that in normal ears (-6.8 +/- 7.8) dB SPL (P < 0.01). The major frequency range of SOAE (0.693-3.055 kHz) in MOCS dysfunction ears was essentially consistent with that of efferent suppression in normal ears (0.7-3 kHz). CONCLUSION: The modulation of the cochlear active mechanisms by MOCS mainly presents in the low- and mid-frequency regions, these frequencies correspond to the frequency range of SOAE. Stronger SOAE indicates pathophysiological significance. There is a clear clinical relationship between SOAE and the efferent modulation of the cochlea.     

豚鼠畸变产物耳声发射潜伏期的对侧抑制效应现象

目的 通过观察对侧抑制效应中畸变产物耳发射（distortion productotoacousticemissions,DPOAE)各指标的改变,探讨耳蜗生理机制及传出神经的调节机能。方法 12只健康杂色豚鼠分A、B2组,在对侧耳无声刺激及给予70dB SPL宽带噪声条件下,分别使用不同的原始纯音强度组合测定在f2＝2、4、6kHz时测试耳DPOAE之幅值及潜伏期。次日,A组动物背侧径路开放右耳听泡,圆窗膜给予60mmol/L卡因酸1μL,作用3h后拭去。给药后6h测试右耳无声刺激和给予70dB SPL宽带噪声刺激下,左耳的DPOAE幅值、潜伏期等指标。结果 ①用药前,A组对侧耳给声时以等强度原始音诱发的测试耳DPOAE各频率幅值与给声前基本无变化,而潜伏期显著延长;②用药前,B组对侧耳给声以差强度原始音（L2＝L1－10dB)诱发的测试耳DPOAE在2、4kHz的幅值与给声前相比有显著减小,潜伏期也显著延长;③A组用药后,对侧耳给声对测试耳DPOAE幅值和潜伏期均无显著影响。结论 潜伏期亦是对侧抑制研究中的敏感指标。对侧抑制效应在调制耳蜗转导机制中发挥负反馈作用。     

Contralateral suppression of DPOAE measured in real time

The aim of this study was to measure contralateral suppression of distortion product otoacoustic emissions (DPOAE) in real time. A total of 10 human subjects were studied with a novel device to record DPOAE without signal time averaging, using digital narrow band pass filtering. Real time DPOAE levels were recorded at 2f1-f2 using primary tone settings of f2/f1 = 1.22 and L1 = 70 dB SPL, L2 = 65 dB SPL, at five values of f2 between 2.2 and 7.7 kHz. An acoustic stimulus was applied intermittently to the contralateral ear to cause DPOAE suppression. Characteristic features of contralateral suppression were identified and distinguished from small spontaneous variations in the real time DPOAE signal. Magnitude of suppression increased with contralateral stimulus intensity. Onset latency of suppression was around 43 ms (31-95 ms). Potential clinical applications are discussed in the light of these findings, including a role in improving the specificity of neonatal hearing screening.     

Age-related declines in distortion product otoacoustic emissions utilizing pure tone contralateral stimulation in CBA/CaJ mice

One role of the medial olivocochlear (MOC) auditory efferent system is to suppress cochlear outer hair cell (OHC) responses when presented with a contralateral sound. Using distortion product otoacoustic emissions (DPOAEs), the effects of active changes in OHC responses due to the MOC as a function of age can be observed when contralateral stimulation with a pure tone is applied. Previous studies have shown that there are age-related declines of the MOC when broad band noise is presented to the contralateral ear. In this study, we measured age-related changes in CBA/CaJ mice by comparing DPOAE generation with and without a contralateral pure tone at three different frequencies (12, 22, and 37 kHz). Young (n = 16), middle (n = 10) and old-aged (n = 10) CBA mice were tested. DPOAE-grams were obtained using L1 = 65 and L2 = 50 dB SPL, F1/F2 = 1.25, using eight points per octave covering a frequency range from 5.6-44.8 kHz. The pure tone was presented contralaterally at 55 dB SPL. DPOAE-grams and ABR levels indicated age-related hearing loss in the old mice. In addition, there was an overall change in DPOAEs in the middle-aged and old groups relative to the young. Pure tone stimulation was not as effective as a suppressor compared to broadband noise. An increase in pure tone frequency from 12 to 22 kHz induced greater suppression of DPOAEs, but the 37 kHz was least effective. These results indicate that as the mouse ages, there are significant changes in the efficiency of the suppression mechanism as elicited by contralateral narrowband stimuli. These findings reinforce the idea that age-related changes in the MOC or the operating points of OHCs play a role in the progression of presbycusis - age-related hearing loss in mammals.