Acoustic masking reduces the efficiency of communication, prey detection, and predator avoidance in marine mammals. Most underwater sounds fluctuate in amplitude. The ability of harbor porpoises (Phocoena phocoena) to detect sounds in amplitude-varying masking noise was examined. A psychophysical technique evaluated hearing thresholds of three harbor porpoises for 500–2000 ms tonal sweeps (3.9–4.1 kHz), presented concurrently with sinusoidal amplitude-modulated (SAM) or unmodulated Gaussian noise bands centered at 4 kHz. Masking was assessed in relation to signal duration and masker level, amplitude modulation rate (1, 2, 5, 10, 20, 40, 80, and 90 Hz), modulation depth (50%, 75%, and 100%) and bandwidth (1/3 or 1 octave). Masking release (MR) due to SAM was assessed by comparing thresholds in modulated and unmodulated maskers. Masked thresholds were affected by SAM rate with the lowest thresholds (i.e., largest MR was 14.5 dB) being observed for SAM rates between 1 and 5 Hz at higher masker levels. Increasing the signal duration from 500–2000 ms increased MR by 3.3 dB. Masker bandwidth and depth of modulation had no substantial effect on MR. The results are discussed with respect to MR resulting from envelope variation and the impact of noise in the environment.

中文翻译：

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与正弦调幅掩蔽噪声相关的港湾鼠海豚 (Phocoena phocoena) 中 4 kHz 的掩蔽释放

声学掩蔽降低了海洋哺乳动物的通信、猎物检测和捕食者回避的效率。大多数水下声音的振幅都会波动。港湾鼠海豚( Phocoena phocoena)的能力) 检测振幅变化的掩蔽噪声中的声音进行了检查。一项心理物理学技术评估了三个港湾鼠海豚在 500–2000 毫秒音调扫描 (3.9–4.1 kHz) 的听力阈值，同时呈现正弦调幅 (SAM) 或以 4 kHz 为中心的未调制高斯噪声频带。掩蔽评估与信号持续时间和掩蔽电平、幅度调制率（1、2、5、10、20、40、80 和 90 Hz）、调制深度（50%、75% 和 100%）和带宽有关（1/3 或 1 个八度）。通过比较调制和未调制掩蔽物的阈值来评估由 SAM 引起的掩蔽释放 (MR)。掩蔽阈值受 SAM 速率的影响，最低阈值（即最大 MR 为 14.5 dB）在较高掩蔽电平下观察到 1 到 5 Hz 之间的 SAM 速率。将信号持续时间从 500-2000 ms 增加，MR 增加了 3.3 dB。掩蔽带宽和调制深度对 MR 没有实质性影响。讨论了由包络变化和环境中噪声影响导致的 MR 的结果。