Shupak Avi, Sharoni Zohara, Yanir Yoav, Keynan Yoav, Alfie Yechezkel, Halpern Pinchas
Israel Naval Medical Institute, Haifa, Israel.
Otol Neurotol. 2005 Jan;26(1):127-30. doi: 10.1097/00129492-200501000-00023.
Underwater hearing acuity and sound localization are improved by the presence of an air interface around the pinnae and inside the external ear canals.
Hearing threshold and the ability to localize sound sources are reduced underwater. The resonance frequency of the external ear is lowered when the external ear canal is filled with water, and the impedance-matching ability of the middle ear is significantly reduced due to elevation of the ambient pressure, the water-mass load on the tympanic membrane, and the addition of a fluid-air interface during submersion. Sound lateralization on land is largely explained by the mechanisms of interaural intensity differences and interaural temporal or phase differences. During submersion, these differences are largely lost due to the increase in underwater sound velocity and cancellation of the head's acoustic shadow effect because of the similarity between the impedance of the skull and the surrounding water.
Ten scuba divers wearing a regular opaque face mask or an opaque ProEar 2000 (Safe Dive, Ltd., Hofit, Israel) mask that enables the presence of air at ambient pressure in and around the ear made a dive to a depth of 3 m in the open sea. Four underwater speakers arranged on the horizontal plane at 90-degree intervals and at a distance of 5 m from the diver were used for testing pure-tone hearing thresholds (PTHT), the reception threshold for the recorded sound of a rubber-boat engine, and sound localization. For sound localization, the sound of the rubber boat's engine was randomly delivered by one speaker at a time at 40 dB HL above the recorded sound of a rubber-boat engine, and the diver was asked to point to the sound source. The azimuth was measured by the diver's companion using a navigation board.
Underwater PTHT with both masks were significantly higher for frequencies of 250 to 6000 Hz when compared with the thresholds on land (p <0.0001). No differences were found in the PTHT or the reception threshold for the recorded sound of a rubber-boat engine for dry or wet ear conditions. There was no difference in the sound localization error between the regular mask and the ProEar 2000 mask.
The presence of air around the pinna and inside the external ear canal did not improve underwater hearing sensitivity or sound localization. These results support the argument that bone conduction plays the main role in underwater hearing.
耳廓周围和外耳道内存在空气界面可改善水下听力敏锐度和声音定位。
水下听力阈值和定位声源的能力会降低。当外耳道充满水时，外耳的共振频率会降低，并且由于环境压力升高、鼓膜上的水体负载以及潜水时增加的液 - 气界面，中耳的阻抗匹配能力会显著降低。陆地上的声音侧向化很大程度上由双耳强度差异和双耳时间或相位差异机制来解释。在潜水时，由于水下声速增加以及头骨与周围水的阻抗相似导致头部声影效应消除，这些差异在很大程度上会消失。
10名潜水员戴着普通不透明面罩或能使耳朵内外在环境压力下存在空气的不透明ProEar 2000（以色列霍菲特Safe Dive有限公司）面罩，在公海潜水至3米深度。四个水下扬声器水平间隔90度、距离潜水员5米布置，用于测试纯音听力阈值（PTHT）、橡皮艇发动机录制声音的接收阈值以及声音定位。对于声音定位，橡皮艇发动机的声音由一个扬声器每次随机以比橡皮艇发动机录制声音高40 dB HL的强度发出，要求潜水员指向声源。方位由潜水员的同伴使用导航板测量。
与陆地上的阈值相比，两种面罩下250至6000 Hz频率的水下PTHT均显著更高（p <0.0001）。在干耳或湿耳条件下，PTHT或橡皮艇发动机录制声音的接收阈值未发现差异。普通面罩和ProEar 2000面罩之间的声音定位误差没有差异。
耳廓周围和外耳道内存在空气并不能改善水下听力敏感度或声音定位。这些结果支持骨传导在水下听力中起主要作用的观点。
