ANTIMASKING EFFECTS OF THE OLIVOCOCHLEAR REFLEX .2. ENHANCEMENT OF AUDITORY-NERVE RESPONSE TO MASKED TONES
ANTIMASKING EFFECTS OF THE OLIVOCOCHLEAR REFLEX .2. ENHANCEMENT OF AUDITORY-NERVE RESPONSE TO MASKED TONES
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DOI：
10.1152/jn.1993.70.6.2533
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发表时间：
1993-12-01
影响因子：
2.5
通讯作者：
LIBERMAN, MC
中科院分区：
文献类型：
--
作者：
KAWASE, T;DELGUTTE, B;LIBERMAN, MC
1.通过比较单个听神经纤维(ANF)对连续掩蔽噪声中的短纯音刺激的反应，研究了麻醉猫和去大脑猫橄榄耳蜗区(OC)传出反馈的抗掩蔽效应。响应被测量为短音强度、短音频率和掩蔽器强度的函数，并被分析，以便能够定量地估计短音在噪声背景下的可检测性。增加对侧OC激发剂既增加了对掩蔽短纯音爆发的最大放电频率，又降低了对同侧掩蔽的最大放电频率。对短声突发率的增加可以解释为由于对掩蔽者的稳定反应的降低而导致的适应性的降低。其结果是屏蔽音突发的速率-水平函数变陡，并且随之而来的是小增量音突发强度的估计可区分性的增加。3.对于光纤特征频率(CF)处的单音突发，OC对掩蔽单音突发的检测阈值的影响取决于掩蔽级别，低掩蔽级别的阈值增加幅度较小，而较高掩蔽级别的阈值下降幅度较大。对于低于CF的音调脉冲串，OC效应在存在时总是降低检测阈值。4.CFS在6~12 kHz之间，掩蔽层水平在掩蔽层阈值的20分贝以内时，抗掩蔽效应最大。这些趋势似乎适用于所有自发频率(SRS)的纤维。.5.当阈值灵敏度接近-10dBSPL时，激活纤维中的OC可引起对非掩蔽音突发反应的增强和随之而来的“自发频率”的降低。当动物发出的噪音产生被OC活动抑制的持续反应(在没有特意应用的声音的情况下)时，这种“安静中的增强”似乎就会出现。这一发现引发了人们对猫“真实”自发频率范围的质疑。6.实验结果突出了在安静和噪声条件下的OC反馈效应之间的两个重要区别。在安静的情况下，这种影响主要是抑制的，并且仅限于接近光纤的CF的频率和其动态范围内的强度的刺激。在连续背景噪声中，OC反射能增强对瞬变刺激的反应。这样的影响在整个光纤的响应区都能看到。由于真正的安静只有在人工实验室条件下才能想象到，在自然声音环境中，OC反射的主要作用是增强对瞬时刺激的反应，因为它抑制了对稳定背景的反应。
1. The antimasking effects of olivocochlear (OC) efferent feedback were studied in anesthetized or decerebrate cats by comparing responses of single auditory-nerve fibers (ANFs) to tone bursts in continuous masking noise seen with and without addition of a moderate-level contralateral noise known to activate the OC reflex. Responses were measured as a function of tone-burst intensity, tone-burst frequency, and masker intensity and were analyzed so as to allow quantitative estimates of the detectability of the tone bursts against the noise background.2. Addition of the contralateral OC elicitor both increased the maximum discharge rates to the masked tone bursts and decreased the rates to the ipsilateral masker. The rate increases to the tone bursts could be explained on the basis of a decrease in adaptation caused by decreasing the steady response to the masker. The result is a steepening of the rate-versus-level function for masked tone bursts and a concomitant increase in the estimated discriminability of small increments of tone-burst intensity. 3. For tone bursts at the fiber's characteristic frequency (CF), the OC effects on detection threshold for the masked tone bursts depended on masker level, with small increases in threshold for low masker levels and somewhat larger decreases in threshold for higher masker levels. For tone bursts below CF, OC effects, when present, always decreased the detection threshold. 4. The largest antimasking effects were seen for fibers with CFs between 6 and 12 kHz and for masker levels within 20 dB of the fiber's threshold to the masker. These trends appeared to hold for fibers of all spontaneous rates (SRs). .5. Enhancement of the response to unmasked tone bursts and concomitant decrease in the ''spontaneous rate'' was elicited by OC activation in fibers if threshold sensitivity approached - 10 dB SPL. This ''enhancement-in-quiet'' appears to arise when an animal-generated noise produces a continuous response (in the absence of purposely applied sound) that is suppressed by OC activity. This finding raises questions as to the range of ''true'' spontaneous rates in the cat. 6. The results highlight two important distinctions between the effects of OC feedback in quiet versus those in noise. In quiet, the effects are predominately suppressive and are restricted to stimuli at frequencies near a fiber's CF and at intensities within its dynamic range. In continuous background noise, the OC reflex can enhance the responses to transient stimuli. Such effects are seen throughout the fiber's response area. Because true quiet is only conceivable under artificial laboratory conditions, the predominant effect of the OC reflex in a natural sound environment is to enhance the response to transient stimuli as it suppresses the responses to steady backgrounds.