Acton, Australia— In a paper published in the Journal of Hearing Science, Dr Andrew Bell of the Research School of Biology at Australian National University (ANU) urges reconsideration of the long-discarded “pressure theory,” a 150-year-old theory on how the ear protects itself from damage caused by loud sounds.
Bell said in an ANU press release that his revised pressure theory has the potential to lead to better measures for protecting people from damagingly loud sound levels, such as MP3 players.
As hearing health professionals know, the middle ear consists of three tiny bones and two miniature muscles which tense up to protect the ear from loud sounds. Bell said that these bones and muscles work together as a tiny pump, raising the pressure of the fluid in the inner ear, like pushing a cork into a bottle of water.
According to Bell, the increased pressure softens the impact of loud noises on the delicate cells that process sound. More specifically, Bell summarized his theory in his abstract, "…the hypothesis [is] made that static pressure in the cochlear fluids is sensed by the outer hair cells, which are in continuous hydraulic connection with the stapes. It is this factor which reduces the gain of the cochlear amplifier and provides rapid and effective overload protection."
Bell believes that utilizing this revised pressure theory may help researchers to understand why some people have "tough" ears that seem impervious to noise-induced hearing loss while others are very susceptible.
“If we can find a way to make the middle ear muscles ‘pump’ more effectively, like they seem to do in tough ears, we could provide better protection against noise,” Bell commented.
Bell cites some contradictions in some modern hearing studies and believes that his revised pressure theory can help explain these inconsistencies.
He said, “All the evidence over the last century can be fitted neatly into pressure theory once you see that the sensing cells in the inner ear are tiny pressure gauges that react instantly to pressure changes.”
Bell’s abstract and full paper, "How do middle ear muscles protect the cochlea? Reconsideration of the intralabyrinthine pressure theory" can be downloaded free here.