Soft tissue conduction is the third mode of auditory stimulation

Abstract

The article by Hosoi et al. “Cartilage conduction as the third pathway for sound transmission” [ [1] Hosoi H. Nishimura T. Shimokura R. Kitahara T. Cartilage conduction as the third pathway for sound transmission. Auris Nasus Larynx. 2019; 46: 151-159 Abstract Full Text Full Text PDF PubMed Scopus (14) Google Scholar ] states that cartilage conduction is the third pathway, in addition to air conduction (AC) and bone conduction (BC), for sound transmission to the ear. That conclusion is based on their analysis that cartilage conduction is distinct from AC and BC. However, the classification of sound transmission pathways leading to auditory sensation should be based on the nature of the physical medium through which the sound induced vibrations are conducted to the hair cells of the inner ear, and excite them. Thus in air conduction, the vibrations induced in air are conducted to the tympanic membrane, middle ear ossicles, inner ear fluids, leading to their vibration and to a traveling wave along the basilar membrane. In bone conduction, the vibrations induced in skin overlying skull bone (usually at the mastoid or the forehead) are conducted to the temporal bone, leading to the four recognized mechanisms of BC (the occlusion effect-“Sound pressure in the external ear canal caused by BC stimuli is elevated – when the opening of the external ear canal is occluded” due to vibrations of the canal wall inducing air pressure in the occluded cavity, ossicle inertia, inner ear fluid inertia, inner ear distortion-compression) [ [2] Stenfelt S. Goode R.L. Bone-conducted sound: physiological and clinical aspects. Otol Neurotol. 2005; 26: 1245-1261 Crossref PubMed Scopus (294) Google Scholar ]. According to their analysis of cartilage conduction, the vibrations of the cartilage of the aural cartilage, cavum concha and the cartilaginous part of the external ear canal induce vibrations of the air in the canal which drives the tympanic membrane, ossicles and inner ear fluid [ [3] Nishimura T. Hosoi H. Saito O. Miyamae R. Shimokura R. Yamanaka T. et al. Cartilage conduction is characterized by vibrations of the cartilaginous portion of the ear canal. PLoS ONE. 2015; 10e0120135https://doi.org/10.1371/journal.pone.0120135 Crossref PubMed Scopus (31) Google Scholar , [4] Nishimura T. Hosoi H. Saito O. Miyamae R. Shimokura R. Matsui T. et al. Is cartilage conduction classified into air or bone conduction?. Laryngoscope. 2014; 124: 1214-1219 Crossref PubMed Scopus (28) Google Scholar . They refer to this as the cartilage-air pathway. In this sense, the cartilage conduction- cartilage-air pathway seems not so much different from the occlusion effect component in BC.