Age-related hearing loss affects around 40% of older people. It causes many people to have great difficulty understanding speech and therefore contributes to social exclusion, isolation, depression, and possibly even the development of dementia. Hearing aids and cochlear implants help, but they are not a substitute for normal hearing and most sufferers continue to have significant problems. There is no treatment for the underlying disease. My research team has developed a microscope that allows us to directly observe the sensory cells of the inner ear when the ear is hit by sound - we can 'see how we hear'. No other group has the technical capabilities for such experiments and we can thus generate unique data. With the microscope, we have discovered a new mechanism of great importance for hearing. Sensory cells contain stereocilia, whose mechanically sensitive ion channels translate sound waves into electrical signals. We have found that the function of stereocilia is regulated by the electrical voltage of the surrounding fluid. If the voltage is reduced, the stereocilia become so soft that they no longer function. Low electrical voltage is the most common cause of age-related hearing loss, so our results have direct relevance to understanding this condition. This project studies how stereocilia function is regulated at the molecular level. This knowledge is being used to develop new treatments for age-related hearing loss.