Department of Mathematical and Life Sciences, Hiroshima University, Department of Sciences, Higashi-Hiroshima, Japan.
Program of Mathematical and Life Sciences, Hiroshima University, Department of Sciences, Higashi-Hiroshima, Japan.
PLoS Comput Biol. 2022 Oct 7;18(10):e1009784. doi: 10.1371/journal.pcbi.1009784. eCollection 2022 Oct.
Bats perceive the three-dimensional environment by emitting ultrasound pulses from their nose or mouth and receiving echoes through both ears. To determine the position of a target object, it is necessary to know the distance and direction of the target. Certain bat species that use a combined signal of long constant frequency and short frequency modulated ultrasounds synchronize their pinnae movement with pulse emission, and this behavior has been regarded as helpful for localizing the elevation angle of a reflective sound source. However, the significance of bats' ear motions remains unclear. In this study, we construct a model of an active listening system including the motion of the ears, and conduct mathematical investigations to clarify the importance of ear motion in direction detection of the reflective sound source. In the simulations, direction detection under rigid ear movements with interaural level differences was mathematically investigated by assuming that bats accomplish direction detection using the amplitude modulation in the echoes caused by ear movements. In particular, the ear motion conditions required for direction detection are theoretically investigated through exhaustive simulations of the pseudo-motion of the ears, rather than simulations of the actual ear motions of bats. The theory suggests that only certain ear motions, namely three-axis rotation, allow for accurate and robust direction detection. Our theoretical analysis also strongly supports the behavior whereby bats move their pinnae in the antiphase mode. In addition, we suggest that simple shaped hearing directionality and well-selected uncomplicated ear motions are sufficient to achieve precise and robust direction detection. Our findings and mathematical approach have the potential to be used in the design of active sensing systems in various engineering fields.
蝙蝠通过从鼻子或嘴巴发出超声波脉冲，并通过两只耳朵接收回波来感知三维环境。为了确定目标物体的位置，需要知道目标的距离和方向。某些使用长恒定频率和短频率调制超声波的组合信号的蝙蝠物种会将其耳郭的运动与脉冲发射同步，这种行为被认为有助于定位反射声源的仰角。然而，蝙蝠耳郭运动的意义仍不清楚。在这项研究中，我们构建了一个包含耳郭运动的主动聆听系统模型，并进行数学研究，以阐明耳郭运动在反射声源方向检测中的重要性。在模拟中，通过假设蝙蝠利用耳郭运动引起的回波中的幅度调制来完成方向检测，数学研究了刚性耳郭运动下的方向检测。特别是，通过对耳郭的伪运动进行详尽的模拟，而不是对蝙蝠实际耳郭运动进行模拟，理论上研究了方向检测所需的耳郭运动条件。该理论表明，只有某些耳郭运动，即三轴旋转，才能实现准确和稳健的方向检测。我们的理论分析还强烈支持蝙蝠以反相模式移动耳郭的行为。此外，我们建议简单的听力方向性和精心选择的不复杂的耳郭运动足以实现精确和稳健的方向检测。我们的研究结果和数学方法有可能用于各种工程领域的主动传感系统的设计。
