Department of Psychology, University of Minnesota, Minneapolis, Minnesota 55455, USA.
J Acoust Soc Am. 2020 Dec;148(6):3581. doi: 10.1121/10.0002879.
Recent studies on amplitude modulation (AM) detection for tones in noise reported that AM-detection thresholds improve when the AM stimulus is preceded by a noise precursor. The physiological mechanisms underlying this AM unmasking are unknown. One possibility is that adaptation to the level of the noise precursor facilitates AM encoding by causing a shift in neural rate-level functions to optimize level encoding around the precursor level. The aims of this study were to investigate whether such a dynamic-range adaptation is a plausible mechanism for the AM unmasking and whether frequency modulation (FM), thought to be encoded via AM, also exhibits the unmasking effect. Detection thresholds for AM and FM of tones in noise were measured with and without a fixed-level precursor. Listeners showing the unmasking effect were then tested with the precursor level roved over a wide range to modulate the effect of adaptation to the precursor level on the detection of the subsequent AM. It was found that FM detection benefits from a precursor and the magnitude of FM unmasking correlates with that of AM unmasking. Moreover, consistent with dynamic-range adaptation, the unmasking magnitude weakens as the level difference between the precursor and simultaneous masker of the tone increases.
最近关于噪声中音调的调幅（AM）检测的研究报告称，当 AM 刺激之前有噪声前导时，AM 检测阈值会提高。这种 AM 掩蔽的生理机制尚不清楚。一种可能性是，对噪声前导水平的适应通过导致神经率-级函数向优化前导水平周围的水平编码的转移，从而促进 AM 编码，从而实现 AM 掩蔽。本研究的目的是探讨这种动态范围适应是否是 AM 掩蔽的合理机制，以及是否调制（FM），据认为是通过 AM 编码的，也表现出掩蔽效应。在有和没有固定水平前导的情况下测量了噪声中音调的 AM 和 FM 的检测阈值。然后，对表现出掩蔽效应的听众进行测试，使前导水平在较宽范围内波动，以调制对前导水平的适应对后续 AM 检测的影响。结果发现，FM 检测受益于前导，并且 FM 掩蔽的幅度与 AM 掩蔽的幅度相关。此外，与动态范围适应一致，掩蔽幅度随着前导和音调同时掩蔽器之间的水平差的增加而减弱。
