Hearing loss can be devastating: you lose friends, become ever trapped inside your head and alienated from society. Yet, only one in five Americans choose to use a hearing aid. Some ignore their problem, others can’t afford treatment or installing a hearing aid, but really a lot of people choose not to wear a hearing aid because it can be just too unbearable. This might change for the better in the future, though. For instance, scientists at University of California are developing a next-generation hearing aid inspired by songbirds that emulates the human ear as realistically as possible.
Was that a chip or a chirp?
All hearing aids have the same basic parts: a microphone, the tonehook or earhook, the volume control, the on/off switch and the battery door. The microphone picks up sounds and sends them to an amplifier that makes them louder. The hearing aid will make some pitches of sound louder than others, depending on the shape of the hearing loss. But Hearing aids aren’t effective for everyone. Hair cells in the inner ear must pick up the vibrations that the hearing aid sends and convert those vibrations into nerve signals. So, you need to have at least some hair cells in the inner ear for it to work. Moreover, most devices aren’t that well tuned, so must of your environment gets equally amplified – this can drive anyone crazy.
“In a crowded place, it can be very difficult to follow a conversation even if you don’t have hearing deficits,” says UC Berkeley neuroscientist Frederic Theunissen. “That situation can be terrible for a person wearing a hearing aid, which amplifies everything.”
Image your sitting in a crowded bar, at a table with your friends. Despite the racket and rattle around, you have no problem having a conversation with your friends because the human brain and ear work together beautifully to hone in on a particular signal – the rest is just background noise that isn’t processed consciously. With a hearing aid, this sort of differentiation is very difficult. So, the ultimate goal is to build a hearing aid that transmits signals and processes audio much in the way the brain would.
Humans aren’t the only ones capable of differentiating between audio signals. Among other animals that are very apt at this is the songbird. For the past two years, Theunissen and colleagues have analyzed the brain imagery of songbirds to understand how these can distinguish between the chirp of a mate from dozens if not hundreds of strangers. The team eventually identified the exact neurons involved in this process which tune into a signal and remain tuned indifferent of how noisy the environment is. Theunissen calls this an “auditory spotlight”. Imagine you’re looking for your car keys on the dinner table. You have this particular shape, texture and colour that you’re searching for among plates, breadcrumbs and cats. In a similar way to the eye, the ear searchers and finds particular pitches and frequencies – say the voice of your friends at the bar.
“Our brain does all this work, suppressing echoes and background noise, conducting auditory scene analysis,” Theunissen says.
The “auditory spotlight” process has been reproduced in an algorithm, and now the UC team is working with a company to test whether the company can improve performance if installed on conventional hearing aids. This next generation of hearing aids will detect the features of the signal and separate it from any background noise. Unlike a traditional hearing aid, it will have a variable gain so that signal sounds get a boost without distortion, while background sounds are attenuated without being completely muffled out.
“This hearing aid should not eliminate all of the noise or distort the signal,” Theunissen says. “That wouldn’t sound real, and the real sound is the most pleasant and the one that we want to hear.”