National Marine Mammal Foundation, 2240 Shelter Island Drive #200, San Diego, California 92106, USA.
Peraton, 4045 Hancock Street, Suite 210, San Diego, California 92110, USA.
J Acoust Soc Am. 2020 Jan;147(1):388. doi: 10.1121/10.0000557.
Bottlenose dolphins (Tursiops truncatus) depend on sounds at frequencies lower than 30 kHz for social communication, but little information on the directional dependence of hearing thresholds for these frequencies exists. This study measured underwater behavioral hearing thresholds for 2, 10, 20, and 30 kHz sounds projected from eight different positions around dolphins in both the horizontal and vertical planes. The results showed that the sound source direction relative to the dolphin affected hearing threshold, and that directional characteristics of the receiving beam pattern were frequency dependent. Hearing thresholds obtained from two adult dolphins demonstrated a positive relationship between directivity of hearing and stimulus frequency, with asymmetric receiving beam patterns in both the horizontal and vertical planes. Projecting sound from directly behind the dolphin resulted in frequency-dependent increases in hearing threshold up to 18.5 dB compared to when sound was projected in front. When the projector was situated above the dolphin thresholds were approximately 8 dB higher as compared to below. This study demonstrates that directional hearing exists for lower frequencies than previously expected.
宽吻海豚（Tursiops truncatus）依赖于低于 30 kHz 的频率进行社交交流，但对于这些频率的听力阈值的方向性依赖的信息很少。本研究在水平和垂直平面上从海豚周围的八个不同位置测量了水下行为听力阈值，用于 2、10、20 和 30 kHz 的声音。结果表明，声源相对于海豚的方向会影响听力阈值，并且接收波束模式的方向性特征是频率相关的。从两只成年海豚获得的听力阈值表明，听力的方向性与刺激频率之间存在正相关关系，在水平和垂直平面上均具有不对称的接收波束模式。与从前部投射声音相比，直接在海豚后面投射声音会导致频率依赖性的听力阈值增加高达 18.5 dB。当投影仪位于海豚上方时，与下方相比，阈值大约高 8 dB。本研究表明，方向性听力存在于比以前预期更低的频率范围内。
