老年性聋患者不同刺激模式下失匹配负波特征分析

目的观察老年性聋(presbycusis)患者频率差异及持续时间差异失匹配负波(mismatch negativity,MMN)的特征。方法应用美国智听公司SmartEP诱发电位系统,采用被动的Oddball模式对30例老年性聋患者(老年性聋组)、26名老年听力正常者(老年听力正常组)和30名正常青年人(对照组)进行频率差异MMN和持续时间差异MMN检测。结果老年性聋组频率差异MMN潜伏期(202.53±33.75ms)与老年听力正常组(182.48±36.44ms)及对照组(174.23±41.19ms)相比明显延长(P<0.05),而波幅(4.89±1.52μV)与老年听力正常组(5.02±1.63μV)及对照组(5.54±1.58μV)相比差异无统计学意义(P>0.05),老年听力正常组频率差异MMN的潜伏期、波幅与对照组比较差异无统计学意义(P>0.05);老年性聋组持续时间差异MMN潜伏期(243.65±19.40ms)与老年听力正常组(216.47±30.89ms)及对照组(184.68±43.16ms)比较差异均有显著统计学意义(P<0.05),波幅(4.39±1.03μV)与对照组(5.32±1.97μV)比较差异有显著统计学意义(P<0.05),与老年听力正常组(4.73±1.78μV)比较差异无统计学意义(P>0.05);另外,老年性聋组频率差异MMN的潜伏期较持续时间差异MMN潜伏期短(P<0.05),频率差异MMN波幅与持续时间差异MMN波幅差异无统计学意义(P>0.05),老年听力正常组频率差异MMN的潜伏期较持续时间差异MMN潜伏期短(P<0.05),波幅差异无统计学意义(P>0.05),对照组频率差异MMN与持续时间差异MMN潜伏期及波幅差异均无显著统计学意义。结论老年性聋组频率差异及持续时间差异MMN的潜伏期较老年听力正常组及对照组延长,其波幅较对照组小,提示老年性聋患者听皮层可能发生了可塑性变化;老年性聋组持续时间差异MMN与频率差异MMN相比潜伏期长,提示持续时间差异MMN较频率差异MMN更敏感,能够更早的反映其皮层及皮层下的变化。     

老年性聋时域间隔感知能力特征分析北大核心CSCD

目的分析老年性聋患者的时域间隔感知能力,为其临床研究提供参考。方法选取老年性聋患者38例作为研究对象,以非老年的感音神经性聋患者15例以及听力正常青年33例作为对照,分别对其进行纯音测听、最大言语识别率(phonetically balanced maximum,PBmax)测试和听觉时域间隔感知阈值测试(temporal gap detection test,TGDT),获得双耳平均听阈(pure-tone audiometry,PTA)、PBmax和TGDT阈值。结果三组TGDT阈值有显著差异(H=9.163,P<0.01),其中老年性聋显著高于感音神经性聋和正常青年组(H=19.267/24.470,P<0.05)。老年性聋组TGDT阈值与年龄、听力损失呈正相关(rs=0.235/0.268/0.281,P<0.05),其中≥80岁组TGDT阈值明显高于60~69岁和70~79岁组(H=-20.750/-20.812,P<0.05),轻度听力损失程度组TGDT阈值明显低于中度和中重度及以上组(H=-19.846/-17.912,P<0.05)。结论老年性聋患者时域间隔感知能力显著减弱,且年龄、听力损失为影响因素。TGDT联合言语测听可为老年性聋的鉴别诊断提供一定参考依据。     

突发性聋伴耳鸣患者治疗前耳鸣性状分析

目的 分析突发性聋伴耳鸣患者的耳鸣性状及其与听力损失之间的关系,探讨耳鸣对患者影响的评估方法.方法 对56例(56耳)突发性聋伴耳鸣患者行听力检测和耳鸣主观分级(评估)及耳鸣匹配检查.结果 ①耳鸣匹配的频率集中于听力损失的频率范围,耳鸣匹配的类型主要为窄带噪声,匹配响度分布较为广泛;②耳鸣主观分级与匹配类型,响度、听力...     

儿童突发性聋的临床特点及预后分析

目的　通过分析儿童突发性聋患者的临床资料,总结其临床特点,研究影响其预后的相关因素,以指导临床诊断和治疗。方法　回顾分析2011年3月～2018年9月华中科技大学同济医学院附属荆州医院确诊并治疗的68例（71耳）儿童突发性聋患者临床资料,了解患者年龄、性别、患耳侧别、初诊时间、纯音听阈及听力曲线类型、是否伴有耳鸣和眩晕等因素对疗效的影响。结果　本组68例儿童突发性聋患者中,听力曲线类型低频下降型38.2%,高频下降型13.2%,平坦型25%,全聋型23.5%。各型总有效率（痊愈+显效+有效）分别为低频下降型84.6%,高频下降型55.6%,平坦型64.7%,全聋型31.2%。伴有耳鸣者48例（70.6%）,伴发眩晕者16例（23.5%）。经系统治疗痊愈11例（16.2%）,总有效率63.2%。多因素Logistic分析表明,听力曲线类型和初诊时间是两个独立影响儿童突发性聋预后的相关因素。结论　本组儿童突发性聋中伴发耳鸣者占多数,治疗总有效率与成人突发性聋相当。儿童突发性聋预后与听力曲线类型和初诊时间密切相关。     

耳蜗死区在老年性聋患者中的初步临床分析

目的探讨老年性聋患者中耳蜗死区及其分布情况。方法采用均衡噪声阈值检测法检测200例(370耳)老年性聋患者和25例(50耳)正常听力老年人中耳蜗死区分布情况,并比较耳蜗死区与老年性患者听力损失程度、病程以及合并高血压病之间的关系。结果 200例老年性聋患者中有38%(76/200)存在耳蜗死区。其中合并高血压病的老年性聋患者中有45%(56/124)存在耳蜗死区,是否合并高血压病组间耳蜗死区检出差异具有统计学意义(P<0.05)。正常听力老年人中无耳蜗死区,同老年性聋患者中比较差异具有统计学意义(P<0.01)。在不同听力损失程度、病程及合并高血压病的老年性聋患者中耳蜗死区的检出率差异有统计学意义(P<0.05)。结论在老年性聋患者中存在耳蜗死区,并且与听力损失严重程度、病程长短以及是否合并高血压病有关,听力损失程度越重、听力受损时间越长,存在耳蜗死区的可能性越大。     

门诊老年性听力损失调查研究

目的分析60岁以上自觉听力障碍的老年人听力损失概况,探讨老年性聋患者的特点。方法调查门诊老年及老年前期患者110例,男95例,女性15例,平均年龄74.4±12.1岁。其中50岁～59岁者15例,作为老年前期对照;60岁以上老年者95例:60～69岁25例,70～79岁26例,80～89岁32例,90岁以上12例。所有110例患者行纯音测听,31例行鼓室图测试。按照Goodman听力障碍分级法将受试者每耳的听力进行分级,并根据听力曲线形状分类。结果全部110名受试者共220耳中,正常听力65耳,占29.5%;轻度到中重度听力损失131耳,占59.5%;重度以上听力损失24耳,占11%。12耳有传导性听力下降,占5.45%。斜坡下降型听力曲线99耳,占45%;陡降型听力曲线34耳,占15.45%;平坦下降型听力曲线45耳,占20.45%;切迹下降型听力曲线5耳,占2.27%;上升和上升-下降型曲线2耳,占0.91%;全聋2耳,占0.91%;正常听力曲线21耳,占9.55%。鼓室图测试结果,A型曲线33例,占接受该测试受试者的53.23%;Ad型曲线9例,占14.52%;As型曲线6例,占9.68%;C型曲线11例,占17.74%;B型曲线3例,占4.84%。老年性聋患者听力随年龄增长缓慢下降,下降速度大约为10dB/10岁。结论老年聋患者在50岁～70岁听阈整体上保持稳定;在70岁～80岁之间会有一个较为明显的听力下降时期;在80岁以后,高频听阈整体稳定在一个较低水平上。中频听力的下降会造成患者响度感知上的明显衰退。     

老年性聋患者噪声下声源定位能力评估

目的 评估老年性聋患者噪声下声源定位能力,探讨年龄、听力损失对噪声下声源定位能力的影响。方法 同期纳入60岁以上的老年性聋组25例,老年听力正常组、青年听力正常组各25例,完成纯音测听、安静及噪声下声源定位测试和蒙特利尔认知评估（Montreal cognitive assessment,MoCA）,分别获得双耳平均听阈、均方根误差（root-mean-square error,RMSE）、MoCA得分,使用重复测量方差分析和Pearson相关统计检验。结果 （1）三组的声源定位能力有显著差异（F=21.394,P<0.001）,老年性聋组定位能力差于对照组（F=32.819,P均<0.01）;(2)老年性聋组噪声下RMSE与年龄、4fPTA正相关,与MoCA得分负相关（P均<0.05）,且控制认知得分后仍有意义。结论 噪声下声源定位角度识别测试可用于老年空间听觉评估,老年性聋组表现受到年龄、听力损失影响。     

感音神经性聋听力图分型

目的对感音神经性聋不同听力图进行分型,为感音神经性聋提供病因学方面的诊断依据。方法对一年内解放军总医院耳鼻咽喉科门诊就诊的2428耳感音神经聋进行纯音听力检测并进行听力图分型。结果将感音神经性聋听力图分为:缓降型816耳,陡降型627耳,低频型152耳,平坦型404耳,岛状为284耳,钟型73耳,V型20耳,蝶型33耳,峰型19耳。结论对感音神经性聋纯音听力图分型,可加深对各型感音神经性聋病因的认识,以利于探索针对性的防治措施。     

突发性聋伴耳鸣患者耳鸣特征

目的 分析研究突发性聋伴耳鸣患者的耳鸣特点、耳鸣与听力损失的关系、耳鸣对患者的影响程度, 探讨突聋患者耳鸣的产生机制。 方法 突发性聋伴有耳鸣患者231例常规采集病史, 填写耳鸣致残量表(THI)及视觉模拟得分表(VAS), 同时进行纯音听阈测试、耳声发射、耳鸣检测及掩蔽试验等检查。分析患者的耳鸣特点、耳鸣与听力的关系、耳鸣的THI及VAS得分以及它们特点。 结果 ①听力损失特点：低中频下降型20例(占8.7%), 中高频下降型60例(占26.0%), 平坦型44例(占19.0%), 全聋型79例(占34.2%), 不规则型28例(占12.1%);②耳鸣频率:低频耳鸣(≤500 Hz)49例(占21.2%), 中频耳鸣(51～2 000 Hz)54例(23.4%), 高频耳鸣(>2 000 Hz)122例(52.8%), 未匹配6例(占2.6%)。其中听力损失类型为低中频下降型的患者中, 低频、中频、高频耳鸣的比例分别为75%、15%、10%;中高频下降型患者中, 低频、中频、高频耳鸣的比例分别为13.3%、26.7%、60.0%;全聋型患者中, 低频、中频、高频耳鸣的比例分别为17.1%、19.0%、63.3%。听力下降最明显的频率对数与耳鸣频率对数呈线性关系, r=0.592, P<0.01;③耳鸣响度:0～30 dB HL 45例(占19.5%), 31～60 dB HL 60例(占26.0%), 60～90 dB HL 102例(占44.2%), 大于90 dB HL 18例(占27.8%), 未匹配6例(占2.6%)。耳鸣响度与听力损失程度(250～4 000 Hz平均听阈)有相关性, 相关系数r=0.216, P=0.001<0.05。④耳鸣致残级别:按照Newman等依据THI得分将耳鸣残疾分级, 其中1级27例(占11.7%), 2级耳鸣44例(占19.0%), 3级66例(占28.6%), 4级94例(占40.7%)。⑤THI及VAS得分特点:THI得分与听力损失程度无相关性r=0.087, P=0.287>0.05。VAS得分与听力损失程度无相关性r=0.002, P=0.982>0.05。THI得分与耳鸣频率对数无相关性, 相关系数r=-0.056, P=0.402>0.05。VAS得分与耳鸣频率对数无相关性, 相关系数r=-0.003, P=0.970>0.05。THI得分与耳鸣响度无相关性, 相关系数r=0.039, P=0.563>0.05。VAS得分与耳鸣响度无相关性, 相关系数r=0.136, P=0.110>0.05。结论 ①突发性聋伴耳鸣患者中高频耳鸣最常见;②耳鸣频率与听力损失类型显著相关, 低中频下降型以低频耳鸣多见, 而中高频下降型及全聋型以高频耳鸣多见;③听力损失最大的频率与耳鸣的频率有较高的一致性;④突发性聋伴耳鸣患者急性期的耳鸣致残程度以3～4级为多;⑤THI及VAS得分与听力损失的程度、耳鸣的频率、耳鸣的响度均无相关性。     

均衡噪声阈值检测法研究耳蜗死区在感音神经性聋患者耳蜗中的分布

目的探讨在感音神经性聋患者中是否存在耳蜗死区及其分布情况。方法采用均衡噪声阈值检测法检测82例(130耳)感音神经性聋患者和25例(50耳)正常听力者是否存在耳蜗死区,并比较耳蜗死区与性别、年龄、耳别、听力损失程度以及病程的关系。结果 82例感音神经性聋患者中有41.46%(34/82)存在耳蜗死区,正常听力者中无耳蜗死区,两者差异具有统计学意义(P<0.01)。耳蜗死区的存在在性别、年龄和耳别之间无明显差异,而不同听力损失程度、病程的感音神经性聋患者耳蜗死区的检出率差异有统计学意义(P<0.05),听力损失越重,病程越长,检出率越高。33.85%(44/130)受试耳存在耳蜗死区,其中高频区耳蜗存在死区者占23.08%(30/130),低频区耳蜗存在死区者占2.31%(3/130),高低频区同时存在耳蜗死区者占8.46%(11/130),高频耳蜗死区检出率远高于低频区。结论在感音神经性聋患者存在耳蜗死区中,耳蜗死区的存在与听力损失程度及病程有关,听力损失程度越重、听力受损时间越长,存在耳蜗死区的可能性越大。     

Relations between perceptual measures of temporal processing, auditory-evoked brainstem responses and speech intelligibility in noise

This study investigates behavioural and objective measures of temporal auditory processing and their relation to the ability to understand speech in noise. The experiments were carried out on a homogeneous group of seven hearing-impaired listeners with normal sensitivity at low frequencies (up to 1 kHz) and steeply sloping hearing losses above 1 kHz. For comparison, data were also collected for five normal-hearing listeners. Temporal processing was addressed at low frequencies by means of psychoacoustical frequency discrimination, binaural masked detection and amplitude modulation (AM) detection. In addition, auditory brainstem responses (ABRs) to clicks and broadband rising chirps were recorded. Furthermore, speech reception thresholds (SRTs) were determined for Danish sentences in speech-shaped noise. The main findings were: (1) SRTs were neither correlated with hearing sensitivity as reflected in the audiogram nor with the AM detection thresholds which represent an envelope-based measure of temporal resolution; (2) SRTs were correlated with frequency discrimination and binaural masked detection which are associated with temporal fine-structure coding; (3) The wave-V thresholds for the chirp-evoked ABRs indicated a relation to SRTs and the ability to process temporal fine structure. Overall, the results demonstrate the importance of low-frequency temporal processing for speech reception which can be affected even if pure-tone sensitivity is close to normal.     

Temporal intraspeech masking of plosive bursts: effects of hearing loss and frequency shaping.

PURPOSE: The purposes were (a) to compare masking of consonant bursts by adjacent vowels for listeners with and without hearing loss and (b) to determine the extent to which the temporal intraspeech masking can be reduced by a simulated hearing-aid frequency-response shaping. METHOD: Fourteen adults with sensorineural hearing loss and 10 with normal hearing participated. Seven of the participants with hearing loss had flat or gradually sloping audiograms, and 7 had steeply sloping losses. Stimuli consisted of 3 consonant bursts (/t/, /p/, /k/) presented in isolation and in vowel-consonant-vowel combinations using the vowel /a/ with formant transition information removed. Normal-hearing listeners were tested using unfiltered stimuli. Listeners with hearing loss were tested using unfiltered stimuli and stimuli filtered to approximate a hearing aid frequency response prescribed by NAL-R. All listeners were tested under earphones at the most comfortable level for the vowel stimulus. Temporal intraspeech masking was quantified as the threshold shift produced by the adjacent vowels. RESULTS: Average intraspeech masking for listeners with steeply sloping hearing loss was significantly higher than that of normal-hearing listeners and those with flat/gradually sloping losses. Greater intraspeech masking was observed for /t/ and /p/ than for /k/. On average, frequency shaping significantly reduced the amount of intraspeech masking for listeners with steeply sloping hearing losses. Even with appropriate amplification/spectral shaping, however, temporal intraspeech masking remained greater than normal for several individuals. CONCLUSION: Findings suggest that some individuals with steeply sloping losses may need additional signal processing to supplement frequency shaping to overcome the effect of temporal intraspeech masking.     

Acoustic Temporal Modulation Detection in Normal-Hearing and Cochlear Implanted Listeners: Effects of Hearing Mechanism and Development

Temporal modulation detection ability matures over many years after birth and may be particularly sensitive to experience during this period. Profound hearing loss during early childhood might result in greater perceptual deficits than a similar loss beginning in adulthood. We tested this idea by measuring performance in temporal modulation detection in profoundly deaf children and adults fitted with cochlear implants (CIs). At least two independent variables could constrain temporal modulation detection performance in children with CIs: altered encoding of modulation information due to the CI-auditory nerve interface, and atypical development of central processing of sound information provided by CIs. The effect of altered encoding was investigated by testing subjects with one of two different hearing mechanisms (normal hearing vs. CI) and the effect of atypical development was studied by testing two different age groups. All subjects were tested for their ability to detect acoustic temporal modulations of sound amplitude. A comparison of the slope, or cutoff frequency, of the temporal modulation transfer functions (TMTFs) among the four subject groups revealed that temporal resolution was mainly constrained by hearing mechanism: normal-hearing listeners could detect smaller amplitude modulations at high modulation frequencies than CI users. In contrast, a comparison of the height of the TMTFs revealed a significant interaction between hearing mechanism and age group on overall sensitivity to temporal modulation: sensitivity was significantly poorer in children with CIs, relative to the other three groups. Results suggest that there is an age-specific vulnerability of intensity discrimination or non-sensory factors, which subsequently affects sensitivity to temporal modulation in prelingually deaf children who use CIs.     

Modulation detection, modulation masking, and speech understanding in noise in the elderly.

Temporal processing of suprathreshold sounds was examined in a group of young normal-hearing subjects (mean age of 26.0 years), and in three groups of older subjects (mean ages of 54.3, 64.8, and 72.2 years) with normal hearing or mild sensorineural hearing loss. Three experiments were performed. In the first experiment (modulation detection), subjects were asked to detect sinusoidal amplitude modulation (SAM) of a broadband noise, for modulation frequencies ranging from 2-1024 Hz. In the second experiment (modulation masking), the task was to detect a SAM signal (modulation frequency of 8 Hz) in the presence of a 100%-modulated SAM masker. Masker modulation frequency ranged from 2-64 Hz. In the final experiment, speech understanding was measured as a function of signal-to-noise ratio in both an unmodulated background noise and in a SAM background noise that had a modulation frequency of 8 Hz and a modulation depth of 100%. Except for a very modest correlation between age and modulation detection sensitivity at low modulation frequencies, there were no significant effects of age once the effect of hearing loss was taken into account. The results of the experiments suggest, however, that subjects with even a mild sensorineural hearing loss may have difficulty with a modulation masking task, and may not understand speech as well as normal-hearing subjects do in a modulated noise background.     

Measurement of the temporal-modulation transfer function for a single listener with cochlear hearing loss and left-hemisphere damage

The modulation depth required for the detection of sinusoidal amplitude-modulation applied to a white noise carrier was measured as a function of modulation frequency, giving temporal modulation transfer functions (TMTFs). Five adult listeners with normal hearing (mean age 52 years), five elderly listeners with moderate cochlear hearing loss (mean age 66 years) and a single elderly listener (aged 73 years) with moderate cochlear hearing loss and left-hemisphere damage were tested in the right ear at 50 dB SL. The five elderly listeners were matched in audiogram with the brain-damaged listener. Modulation detection was systematically poorer than normal in the five elderly listeners with cochlear hearing loss. However, their TMTFs were lowpass in shape, as for the five normal-hearing adult listeners. Modulation detection was much poorer in the elderly listener with cochlear hearing loss and left-hemisphere damage compared to the five normal-hearing adults and the five elderly listeners with cochlear hearing loss. Moreover, modulation detection was poorer at 4, 64 and 128 Hz than at 8, 16 and 32 Hz in the brain-damaged listener, giving his TMTF a bandpass appearance. These results are in agreement with the hypothesis that the main factors limiting the ability to detect changes in the temporal-envelope of sounds are located at a central (retro-cochlear) level of the auditory system rather than at a peripheral (cochlear) level. They also suggest that the TMTF approach may prove useful in distinguishing peripheral and central hearing losses.     

Sensorineural Hearing Loss and Neural Correlates of Temporal Acuity in the Inferior Colliculus of the C57bl/6 Mouse

Perception of complex sounds depends on the encoding of the dynamic and static structures within the ongoing stimulus by the auditory system. Aging has been associated with deficits in both areas, thus, the difficulty that the elderly have in speech comprehension could due to hearing loss, or to a loss of temporal sensitivity, or some combination of both. We investigated the effects of sensorineural hearing loss (SNHL) on neural correlates of temporal resolution by recording the responses of inferior colliculus neurons to a gap detection paradigm. We used C57BL/6 (C57) strain of laboratory mouse, which carries the Ahl deafness gene that initiates a progressive high frequency SNHL beginning at about 2 months of age and rapidly progresses to total deafness by 18 months. We compared gap encoding from inferior collicular neurons from young, normal-hearing C57 mice and middle-aged, hearing-impaired, C57 mice, quantifying minimal gap threshold, and recovery functions. The proportion of unit types, spontaneous rates and degree of monotonicity were comparable between young and middle-aged C57 mice. As expected, single unit thresholds were elevated by 30–40 dB in middle-aged C57 mice. However, no significant differences in mean minimal gap thresholds or in the slopes of the gap recovery functions were found between the two age groups. Thus, the results suggest that moderate high frequency SNHL does not affect temporal processing as measured by the gap detection paradigm.     

Frequency and temporal resolution in elderly listeners with good and poor word recognition.

There is a subgroup of elderly listeners with hearing loss who can be characterized by exceptionally poor speech understanding. This study examined the hypothesis that the poor speech-understanding performance of some elderly listeners is associated with disproportionate deficits in temporal resolution and frequency resolution, especially for complex signals. Temporal resolution, as measured by gap detection, and frequency resolution, as measured by the critical ratio, were examined in older listeners with normal hearing, older listeners with hearing loss and good speech-recognition performance, and older listeners with hearing loss and poor speech-recognition performance. Listener performance was evaluated for simple and complex stimuli and for tasks of added complexity. In addition, syllable recognition was assessed in quiet and noise. The principal findings were that older listeners with hearing loss and poor word-recognition performance did not perform differently from older listeners with hearing loss and good word recognition on the temporal resolution measures nor on the spectral resolution measures for relatively simple stimuli. However, frequency resolution was compromised for listeners with poor word-recognition abilities when targets were presented in the context of complex signals. Group differences observed for syllable recognition in quiet were eliminated in the noise condition. Taken together, the findings support the hypothesis that unusual deficits in word-recognition performance among elderly listeners were associated with poor spectral resolution for complex signals.     

Perceptual characterization of children with auditory neuropathy

OBJECTIVE: To characterize the perceptual abilities of a group of children with auditory neuropathy (AN)-type hearing loss, correlating results on a range of psychophysical tasks with open-set speech perception performance. DESIGN: Frequency resolution, temporal resolution and frequency discrimination ability was assessed in a group of 14 children with AN. Data also were obtained from a cohort of matched subjects with sensorineural hearing loss, and from a group of normally hearing children. RESULTS: Frequency resolution (notched noise masking) results for the AN subjects were equivalent to those of the normal-hearing subjects reflecting the "normal" outer hair cell function that characterizes the AN condition. Temporal resolution (TMTF) findings were, however, abnormal in many AN subjects and the degree of temporal disruption was correlated with speech discrimination (CNC) score. Frequency discrimination ability (for both fixed and frequency modulated stimuli) was also affected in those children with poor temporal resolution. CONCLUSIONS: The findings of this study indicate that the perceptual profiles of children with AN are quite different from those with sensorineural hearing loss. Where subjects in the latter group presented with impaired frequency resolution and normal temporal processing, the AN subjects typically showed normal frequency resolution and varying degrees of temporal disruption. The severity of this temporal abnormality, which appeared to affect both temporal resolution/amplitude modulation detection and the temporal aspects of frequency discrimination (such as phase locking), was strongly correlated to speech perception performance.     

Measures of signal processing in persons with sensorineural hearing loss below 6 kHz

Estimates of threshold, wide- and narrow-band noise masking, frequency and amplitude modulation detection, gap detection, and rate discrimination were obtained from 10 subjects with near-normal hearing at frequencies above 6 kHz, but severe-to-profound hearing losses at lower frequencies. The same measures were obtained from 10 young control subjects with normal hearing sensitivity for all frequencies up to 16 kHz. The hearing-impaired subjects were able to process sounds in the region of near-normal hearing sensitivity as well as the unimpaired control subjects. Performance in the low-frequency, impaired region depended on the lowest frequency of near-normal hearing sensitivity.     

Temporal modulation transfer functions measured from auditory-nerve responses following sensorineural hearing loss

The ability of auditory-nerve (AN) fibers to encode modulation frequencies, as characterized by temporal modulation transfer functions (TMTFs), generally shows a low-pass shape with a cut-off frequency that increases with fiber characteristic frequency (CF). Because AN-fiber bandwidth increases with CF, this result has been interpreted to suggest that peripheral filtering has a significant effect on limiting the encoding of higher modulation frequencies. Sensorineural hearing loss (SNHL), which is typically associated with broadened tuning, is thus predicted to increase the range of modulation frequencies encoded; however, perceptual studies have generally not supported this prediction. The present study sought to determine whether the range of modulation frequencies encoded by AN fibers is affected by SNHL, and whether the effects of SNHL on envelope coding are similar at all modulation frequencies within the TMTF passband. Modulation response gain for sinusoidally amplitude modulated (SAM) tones was measured as a function of modulation frequency, with the carrier frequency placed at fiber CF. TMTFs were compared between normal-hearing chinchillas and chinchillas with a noise-induced hearing loss for which AN fibers had significantly broadened tuning. Synchrony and phase responses for individual SAM tone components were quantified to explore a variety of factors that can influence modulation coding. Modulation gain was found to be higher than normal in noise-exposed fibers across the entire range of modulation frequencies encoded by AN fibers. The range of modulation frequencies encoded by noise-exposed AN fibers was not affected by SNHL, as quantified by TMTF 3- and 10-dB cut-off frequencies. These results suggest that physiological factors other than peripheral filtering may have a significant role in determining the range of modulation frequencies encoded in AN fibers. Furthermore, these neural data may help to explain the lack of a consistent association between perceptual measures of temporal resolution and degraded frequency selectivity.