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PNAS:蝙蝠可能调整它们的回声定位呼叫从而与环境噪声竞争

一项研究揭示出了进行回声定位的蝙蝠如何改变它们的呼叫的振幅和频率,从而在混乱环境的嘈杂声中通讯。

鸟类、人类和其他哺乳动物本能地提高声音从而与背景噪声竞争——这种现象被称为Lombard效应——但是伴随着动物的这种效应的具体听觉变化仍然不清楚。

Steffen Hage及其同事研究了一种声调很高的哺乳动物——能够进行回声定位的菊头蝠,从而确定在人类中间观察到的增加发音的振幅、频率和词的时长的行为是否类似于蝙蝠的声音变化。这组作者研究了3只蝙蝠,在变化的经过过滤的噪声频率下回放这种蝙蝠的天然的、无Lombard效应的呼叫的时候,它们做出响应而发出的8.3万多次回声定位呼叫的频率和振幅。这组作者测试了背景噪声对各种因素的作用,包括聆听通讯呼叫和低频背景噪声——诸如雨滴落在植被上的声音——的能力。这些蝙蝠对几乎所有背景噪声频率做出响应而增加呼叫频率,但是呼叫的振幅只在背景噪声以通常与回声定位有关的频率上播放的时候才会增加。这组作者指出,蝙蝠通过监测它们自己的声音的回波从而不断调节它们的回声定位脉冲,而且这种针对背景噪声的快速声音调节表明它背后的负责Lombard效应的神经网络可能在没有直接听觉反馈的情况下发挥功能。

这些发现提示了在听觉和语音-运动神经系统之间存在一种直接联系。

了解更多:

Ambient noise induces independent shifts in call frequency and amplitude within the Lombard effect in echolocating bats

PNAS, February 19 | doi:10.1073/pnas.1211533110

The Lombard effect, an involuntary rise in call amplitude in response to masking ambient noise, represents one of the most efficient mechanisms to optimize signal-to-noise ratio. The Lombard effect occurs in birds and mammals, including humans, and is often associated with several other vocal changes, such as call frequency and duration. Most studies, however, have focused on noise-dependent changes in call amplitude. It is therefore still largely unknown how the adaptive changes in call amplitude relate to associated vocal changes such as frequency shifts, how the underlying mechanisms are linked, and if auditory feedback from the changing vocal output is needed. Here, we examined the Lombard effect and the associated changes in call frequency in a highly vocal mammal, echolocating horseshoe bats. We analyzed how bandpass-filtered noise (BFN; bandwidth 20 kHz) affected their echolocation behavior when BFN was centered on different frequencies within their hearing range. Call amplitudes increased only when BFN was centered on the dominant frequency component of the bats’ calls. In contrast, call frequencies increased for all but one BFN center frequency tested. Both amplitude and frequency rises were extremely fast and occurred in the first call uttered after noise onset, suggesting that no auditory feedback was required. The different effects that varying the BFN center frequency had on amplitude and frequency rises indicate different neural circuits and/or mechanisms underlying these changes.

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