Instituto de Neurociencias de Castilla y León, Universidad de Salamanca 37007 Salamanca, Spain; Instituto de Investigación Biomédica de Salamanca, Universidad de Salamanca 37007 Salamanca, Spain.
Departamento de Psicología Experimental, Procesos Cognitivos y Logopedia, Universidad Complutense de Madrid, 28223 Pozuelo de Alarcón, Madrid, Spain.
Hear Res. 2024 Nov;453:109111. doi: 10.1016/j.heares.2024.109111. Epub 2024 Sep 8.
Cochlear tuning and hence auditory frequency selectivity are thought to change in noisy environments by activation of the medial olivocochlear reflex (MOCR). In humans, auditory frequency selectivity is often assessed using psychoacoustical tuning curves (PTCs), a plot of the level required for pure-tone maskers to just mask a fixed-level pure-tone probe as a function of masker frequency. Sometimes, however, the stimuli used to measure a PTC are long enough that they can activate the MOCR by themselves and thus affect the PTC. Here, PTCs for probe frequencies of 500 Hz and 4 kHz were measured in forward masking using short maskers (30 ms) and probes (10 ms) to minimize the activation of the MOCR by the maskers or the probes. PTCs were also measured in the presence of long (300 ms) ipsilateral, contralateral, and bilateral broadband noise precursors to investigate the effect of the ipsilateral, contralateral, and bilateral MOCR on PTC tuning. Four listeners with normal hearing participated in the experiments. At 500 Hz, ipsilateral and bilateral precursors sharpened the PTCs by decreasing the thresholds for maskers with frequencies at or near the probe frequency with minimal effects on thresholds for maskers remote in frequency from the probe. At 4 kHz, by contrast, ipsilateral and bilateral precursors barely affected thresholds for maskers near the probe frequency but broadened PTCs by reducing thresholds for maskers far from the probe. Contralateral precursors barely affected PTCs. An existing computational model was used to interpret the results. The model suggested that despite the apparent differences, the pattern of results is consistent with the ipsilateral and bilateral MOCR inhibiting the cochlear gain similarly at the two probe frequencies and more strongly than the contralateral MOCR.
耳蜗调谐，因此听觉频率选择性被认为在嘈杂环境中通过内侧橄榄耳蜗反射（MOCR）的激活而改变。在人类中，听觉频率选择性通常使用心理声学调谐曲线（PTC）来评估，这是一个纯音掩蔽器所需的水平与掩蔽器频率的函数的图，以刚好掩蔽固定水平的纯音探针。然而，有时用于测量 PTC 的刺激足够长，以至于它们可以自行激活 MOCR，从而影响 PTC。在这里，使用短掩蔽器（30ms）和探针（10ms）在前向掩蔽中测量了 500Hz 和 4kHz 的探针频率的 PTC，以最大程度地减少掩蔽器或探针对 MOCR 的激活。还测量了长（300ms）同侧、对侧和双侧宽带噪声前导对 PTC 调谐的影响。四名听力正常的听众参加了实验。在 500Hz 时，同侧和双侧前导使 PTC 变锐，降低了频率与探针频率相同或接近的掩蔽器的阈值，而对频率远离探针的掩蔽器的阈值影响最小。相比之下，在 4kHz 时，同侧和双侧前导几乎没有影响探针频率附近的掩蔽器的阈值，但通过降低远离探针的掩蔽器的阈值来拓宽 PTC。对侧前导几乎没有影响 PTC。使用现有的计算模型来解释结果。该模型表明，尽管存在明显差异，但结果模式与同侧和双侧 MOCR 在两个探针频率下以相似的方式抑制耳蜗增益并且比对侧 MOCR 更强的模式一致。
