Delgutte B
Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge 02139.
J Acoust Soc Am. 1990 Feb;87(2):791-809. doi: 10.1121/1.398891.
Masking might be due either to the spread of the excitation produced by the masker to the place of the tone signal along the cochlea or to the suppression of the response to the signal by the masker. In order to identify the contributions of these two mechanisms to tone-on-tone masking, masked thresholds of auditory-nerve fibers were measured in anesthetized cats using the same stimulus paradigms and detection criteria as in psychophysics. Suppressive masking was identified by comparing thresholds for simultaneous masking with those for a nonsimultaneous masking technique resembling pulsation thresholds. These nonsimultaneous thresholds do not include the contribution of suppression to masking because suppression only occurs for stimuli that overlap in time. For each masker and signal frequency, the fibers with the lowest (or "best") masked thresholds had characteristic frequencies (CF) slightly on the opposite side of the masker frequency with respect to the signal frequency, consistent with the psychophysical phenomenon of off-frequency listening. Patterns of best masked thresholds against signal frequency resembled psychophysical masking patterns in that they showed a maximum for signal frequencies close to the masker, and a skew toward high frequencies. Masking was found to be both excitatory and suppressive, with the relative contribution of the two mechanisms depending on the frequency separation between signal and masker. Suppressive masking was large for signal frequencies well above the masker. For these conditions, simultaneous thresholds grew more rapidly with masker level than did nonsimultaneous thresholds, suggesting that the upward spread of masking is largely due to the growth of suppression rather than to that of excitation.
掩蔽可能是由于掩蔽声产生的兴奋沿着耳蜗扩散到音调信号所在位置，或者是由于掩蔽声抑制了对信号的反应。为了确定这两种机制对纯音掩蔽的贡献，在麻醉的猫身上，使用与心理物理学相同的刺激范式和检测标准，测量了听神经纤维的掩蔽阈值。通过将同时掩蔽的阈值与一种类似于脉动阈值的非同时掩蔽技术的阈值进行比较，来识别抑制性掩蔽。这些非同时阈值不包括抑制对掩蔽的贡献，因为抑制只发生在时间上重叠的刺激中。对于每个掩蔽声和信号频率，具有最低（或“最佳”）掩蔽阈值的纤维的特征频率（CF）相对于信号频率，在掩蔽声频率的稍另一侧，这与离频聆听的心理物理现象一致。最佳掩蔽阈值相对于信号频率的模式类似于心理物理掩蔽模式，即它们在接近掩蔽声的信号频率处显示出最大值，并向高频倾斜。发现掩蔽既有兴奋性的也有抑制性的，这两种机制的相对贡献取决于信号和掩蔽声之间的频率间隔。对于远高于掩蔽声的信号频率，抑制性掩蔽很大。在这些条件下，同时掩蔽阈值随掩蔽声强度的增长比非同时掩蔽阈值更快，这表明掩蔽的向上扩展主要是由于抑制的增长而不是兴奋的增长。
