Research Article Experimental Analysis of the Mechanism of Hearing under Water Shai Chordekar, 1 Liat Kishon-Rabin, 1 Leonid Kriksunov, 2,3 Cahtia Adelman, 3,4 and Haim Sohmer 5 1 Department of Communication Disorders, Sackler Faculty of Medicine, Tel Aviv University, e Chaim Sheba Medical Center, 52621 Tel Hashomer, Israel 2 Ozen Kashevet Hearing Clinic, 6 Ben Maimon Street, 92261 Jerusalem, Israel 3 Department of Communication Disorders, Hadassah Academic College, 37 Haneviim Street, P.O. Box 1114, 91010 Jerusalem, Israel 4 Speech & Hearing Center, Hebrew University School of Medicine, Hadassah Medical Center, Kiryat Hadassah, P.O. Box 12000, 91120 Jerusalem, Israel 5 Department of Medical Neurobiology (Physiology), Institute for Medical Research Israel-Canada, Hebrew University, Hadassah Medical School, P.O. Box 12272, 91120 Jerusalem, Israel Correspondence should be addressed to Haim Sohmer; haims@ekmd.huji.ac.il Received 26 August 2015; Revised 11 November 2015; Accepted 24 November 2015 Academic Editor: Jareen K. Meinzen-Derr Copyright © 2015 Shai Chordekar et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. e mechanism of human hearing under water is debated. Some suggest it is by air conduction (AC), others by bone conduction (BC), and others by a combination of AC and BC. A clinical bone vibrator applied to soſt tissue sites on the head, neck, and thorax also elicits hearing by a mechanism called soſt tissue conduction (STC) or nonosseous BC. e present study was designed to test whether underwater hearing at low intensities is by AC or by osseous BC based on bone vibrations or by nonosseous BC (STC). resholds of normal hearing participants to bone vibrator stimulation with their forehead in air were recorded and again when forehead and bone vibrator were under water. A vibrometer detected vibrations of a dry human skull in all similar conditions (in air and under water) but not when water was the intermediary between the sound source and the skull forehead. erefore, the intensities required to induce vibrations of the dry skull in water were significantly higher than the underwater hearing thresholds of the participants, under conditions when hearing by AC and osseous BC is not likely. e results support the hypothesis that hearing under water at low sound intensities may be attributed to nonosseous BC (STC). 1. Introduction Even though the mammalian ear is adapted mainly for hear- ing in an air environment, that is, by air conduction (AC), involving the tympanic membrane and the middle ear ossicu- lar chain, mammals including humans also hear under water [1–5]. However, the mechanism responsible for the hearing of sound in water is still not clear. Some studies support the tym- panic theory which suggests that when under water, sound waves are conducted to the inner ear via the middle ear as in AC hearing [3]. at is, a passive traveling wave is induced, leading to activation of the outer hair cells [6]. Other studies provided evidence supporting an osseous bone conduction (BC) mechanism for underwater hearing, in which the sound field in the water surrounding the head induces skull bone vibrations that are necessary for eliciting BC hearing [1, 2, 5]. ese bone vibrations lead to ossicular chain inertia, cochlear compression-distortion, cochlear fluid inertia, and radiation to the external canal, if occluded (occlusion effect) [7]. Some researchers have suggested a dual path theory of underwater hearing which assumes that both mechanisms, AC and BC, are involved in underwater hearing [2, 3]. Recently, further analysis of the mechanisms of BC has led to the suggestion that during low intensity BC stimulation hearing can result from transmission of sound waves to the inner ear via soſt tissue and fluid pathways, for example, by Hindawi Publishing Corporation BioMed Research International Volume 2015, Article ID 526708, 7 pages http://dx.doi.org/10.1155/2015/526708