https://www.scientificamerican.com/article/light-beam-lets-the-deaf-gerbil-hear/

Some half a million people worldwide with severe hearing loss use an electronic implant in the ears to be able to let them understand speech. Cochlear implants, as they are known, are one of the most successful technologies to have come out of neuroscience, but only provide partial correction for any hearing deficit. They are not a bionic device that lets people enjoy a Mozart symphony or make out a friend’s gossip in the din of an outing at a local club. “If they go to a restaurant, it’s very hard for them to understand speech,” says auditory neuroscientist Tobias Moser of the University of Goettingen in Germany. “They also suffer from not appreciating melodies.”

Cochlear implants have a maximum of 22 channels to perceive the frequency of an utterance. New research led by Moser has the potential to overcome these limitations by using light to precisely stimulate auditory neurons in the inner ear. Moser hopes the approach may one day improve the current generation of cochlear implants and make speech in noisy environments comprehensible for deaf people.