What Noise Does to the Ears
The British-German hearing researcher Geoffrey Manley has spent many decades studying the hearing of reptiles, birds and mammals, including humans. He spent 15 years as a visiting researcher at the Cluster of Excellence Hearing4all. Recently, Manley published his new book, “Ears wide open”. It is available on various platforms, for example here (https://atmospherepress.com/books/ears-wide-open-the-why-and-how-to-protect-your-ears-by-geoffrey-a-manley/), as a paperback or e-book. An interview about hearing, noise, and what we can do to protect our ears.
What are the advantages of the ears compared to other sensory systems such as the eyes and the nose?
Of course, it is difficult to compare the various sensory organs and things like sound, odours, and light directly with each other. The great advantage of hearing is that it does not rely on light, and the position of the body also plays hardly any role in this kind of sensory perception. Animals and humans can hear sounds from completely different directions, regardless of the time of day and without having to orient themselves towards the source. Another advantage is that producing sound when speaking requires far less energy than visual communication – for example, when I wave to someone with an arm movement rather than calling out. Verbal communication therefore saves energy that we can use for other things. Through my book, I aim to kindle an interest in hearing as a miracle of nature, but also to clearly demonstrate that our auditory system is easily damaged and requires greater protection.
What is human hearing like?
When we look at the evolutionary history of primates, to which we humans also belong, we see that over time, body size has increased whilst the ability to produce and hear high frequencies has decreased. Smaller monkeys often have a hearing range extending up to frequencies of 40 or 50 kilohertz. Chimpanzees, gorillas and humans tend to reach only 16 to 20 kilohertz. Our inner ear is structured in such a way that it offers more space for processing low frequencies than for high frequencies. Low frequencies can go around obstacles more easily than high-frequency sounds, and they also have a greater range. It is therefore an evolutionary advantage to be able to hear low frequencies.
Human ears can also produce sounds known as otoacoustic emissions. How can we make use of this?
In the late 1980s, experiments revealed that the human ear can produce sounds immediately after being exposed to short click sounds. A few years later, it was discovered that these otoacoustic emissions, which originate in the ear, can not only be artificially induced but that the ear can also produce them spontaneously. This knowledge can be put to good use, for example by playing sounds to different parts of the inner ear and checking whether that induces otoacoustic emissions. If it does, this indicates that the inner ear is functioning properly. Spontaneous emissions also offer the opportunity to investigate the mechanisms of sensory cell function objectively and non-invasively in great detail.
One of the book’s main focuses concerns health problems relating to hearing. What role does noise play in the development of hearing loss, particularly when compared with other factors such as age?
Researchers found in early studies that residents of remote villages in Sudan and on Easter Island in the Pacific have significantly better hearing in old age than their peers in Western countries. In particular, hearing loss at high frequencies is much less pronounced in elderly people there as they age than it is among elderly people in Europe and the USA. Older study participants in the US were only able to hear certain high-frequency sounds when they were played at a volume 60 decibels higher than for younger participants. This means that, compared to younger people, these older Americans require approximately a thousand times the sound pressure to hear a high-pitched sound, whilst for the inhabitants of Easter Island, ten times the sound pressure is sufficient. This demonstrates that, whilst age does have an impact on our hearing ability, other factors such as noise play a greater role.
In your book, you refer to noise as “one of the most harmful and pervasive evils of modern society”. You say it damages our hearing, is a source of psychological stress and can even cause high blood pressure. What can we do in our daily lives to combat this “evil”?
Noise can damage our hearing in two ways. On the one hand, noise – that is, high sound pressure – directly damages our hearing; on the other hand, it also causes stress, which can be a contributing factor to high blood pressure. And high blood pressure, in turn, can damage the sensitive inner ear. But we can do something about it! The best thing is not to expose yourself to loud noises in the first place – in other words, to avoid them, for example by turning down the music. You should also always wear hearing protection whenever you’re working with loud machines, such as vacuum cleaners or lawnmowers. I’d set the threshold for this at 75 decibels. Every machine, or its user manual, has a label with information on its noise level. Any protection is better than none: at a loud concert, if you’ve forgotten your hearing protection, it can help to stuff pieces of dampened tissues into your ears. I would also like to see more political regulation of noise sources – such as at public music performances – to protect the hearing health of the listeners. For example, the authorities should mandate that, where technically feasible, devices be quieter. International competitions to see who can produce the quietest devices would also be welcome.
If children suffer from hearing impairments, this can have a negative impact on their brain development. What measures are available to help children affected by this?
Cochlear implants (CI) are very effective when the auditory nerve is still functioning, as many genetic disorders affect the sensory hair cells of the inner ear, not the nerves. However, particularly in the case of complex genetic disorders involving several genes, treatment is unfortunately very difficult. If “only” one gene is affected, treatment has recently become significantly easier. This is because the first therapies are now available that involve replacing a single gene linked to the hearing function. In the case of the genetic defect “otoferlin deafness”, signals cannot be transmitted to the auditory nerve because the protein otoferlin, which is necessary for this process, does not function properly in the sensory cells. This new gene therapy involves doctors surgically introducing a healthy gene into the inner ear. To do this, using a thin catheter, they create an access point to the inner ear so that a harmless virus can act as a “taxi” to deliver the intact gene there. Initial trials have been successful in children, meaning that most of the treated children can now hear! The therapy has therefore already been approved in the USA. Such gene therapies are particularly effective when started early in life, since as a person ages, the nerve fibres die off first, followed by the sensory cells – and these cells cannot yet be replaced.
You write that children should be taught to be quiet as early as possible in their life. But isn’t it in children’s nature also to be loud sometimes?
That’s a good question. After all, a great deal is in the nature of children – and of people in general, such as aggression – and we try to channel this in a positive direction through nurture and education. It’s clear to me that, particularly in schools and nurseries, the noise levels are often too high. If children and teachers are exposed to these levels for too long, it can be harmful to their hearing and general health. As a society, we should see it as our responsibility to teach children from an early age to be a little quieter. Of course, children should be allowed to shout or be loud now and then, but a constantly high noise level isn’t good for anyone. It would be good if we all got used to a quieter environment from an early age. We put up with far too much din in our lives!
One of the most common hearing problems is tinnitus. What causes it, and what are current treatment approaches?
Tinnitus is often associated with hearing loss. Research has shown that, in cases of hearing loss, the nerve cells in the ear that transmit sounds at medium volume levels are the first to fail. These medium levels are particularly important for understanding spoken language. When these cells die off, the brain also changes how it processes sensory inputs, as information has been lost. It is thought that when certain nerve pathways to the brain are cut off, the brain amplifies other pathways in a way that serves no “purpose”. Tinnitus is therefore likely a phantom sensation, apparently based on this abnormal brain activity. To this day, effective treatments remain scarce. One approach involves CIs, as these create new input pathways, but CIs are only appropriate in severe cases.
You also warn against stigmatising deafness. In particular, some people who have been deaf since birth would not see their deafness as a disability, but as a “cultural trait”. How can society treat these people with respect?
We should support them as best we can. Many of them have, of course, set up groups where they can communicate very well with one another, for example through sign language. It is remarkable how many people with congenital deafness cope very well with their disability. And that is why I see absolutely no reason to put any pressure on these people to use a hearing aid or a CI. Instead, we should do our bit to ensure that they can lead a happy, self-determined life.
Interview: Henning Kulbarsch
About the person: Geoffrey Manley is a neurobiologist and physiologist. He studied at Cambridge (UK) and Princeton (USA). From 1970 to 1978, he worked at McGill University in Montreal, before serving as Professor of Zoology at the Technical University of Munich from 1980 to 2011. Following his retirement, he was a visiting researcher at the Carl von Ossietzky University of Oldenburg from 2010 to 2025 as part of the Cluster of Excellence Hearing4all. His main areas of research include the evolution of the vertebrate ear, together with that of the human ear, as well as non-invasive methods for investigating cochlear function, particularly the biophysics of otoacoustic emissions in animals and humans. Manley has published over 200 papers and other publications.
