A ‘deaf generation’ exposed to constant noise may be losing the ability to hear as nature intended, a sound expert has claimed.

As a result they could be missing out on effects from natural sounds that contribute to good health and well-being, research suggests.

Kurt Fristrup, who has monitored sound levels in 90 US national parks including Yosemite, Grand Teton and the Grand Canyon, stressed that hearing is a “universal learning sense” active even when we are sleeping or anaesthetised.

Speaking at the American Association for the Advancement of Science (AAAS) annual meeting in San Jose, California, he said: “It’s not surprising since we’re seeing more rapid growth in noise and in population in our cities, and the built environment is providing lots of cues that we find annoying or aren’t relevant to us, that people are putting on earphones or even noise-cancelling earphones, to just try and create a quieter or more congenial environment.

“Of course what they’re missing, what’s being lost, is the ability to hear threats that are real. It’s the cry wolf phenomenon. There will be the occasional cue that really matters − for runners I worry about this − but more importantly, even in our cities there are birds; there are things to appreciate in the environment as well.

“That’s being lost, and what I really worry about is when that generation of visitors comes to national parks they just may not be able to reach out with their ears and experience everything there is.”

He explained that he was used to being aware of the sounds of aircraft that often went unnoticed by his friends.

“I often ask them at the end of the day, did they notice the aircraft noise, and they say, well, I may have heard one or two aircraft,” he said. “Of course I’m counting them, like 17 jets and three G8 aircraft and one helicopter, and most people are astonished when I tell them that.”

Exposure to natural sounds speeded up recovery from stress

Fristrup suspected that our sensitivity to sound stems from our early ancestors, whose survival depended on listening out for predators.

“Our ancestors were probably quite anxious little apes,” he said. “They weren’t the fastest or best armed thing around and there were a lot of predators. I suspect there are certain auditory conditions... when a predator enters the scene all the other organisms are going to change their behaviour.

“And I suspect there’s something about these (natural) soundscapes that reminds our ancestral brains of a place that is safe.

“Even for people who are interested in nature and who go out and spend a lot of time there, this gift that we’re born with, to reach out and hear things that are hundreds of metres away, is in danger of being lost. It’s a generational amnesia problem.”

Fristrup’s work in the national parks has shed light on how well people are able to home in on the sounds around them.

“As you raise background noise it has the same effect on sound that fog has on vision,” he said.

He pointed out that natural parks could be surprisingly noisy. At any given location, the average park had a source of noise 25 per cent of the time, and 100,000 air tours were flown across the Grand Canyon each year.

Recent research has shown that natural sounds, such as tumbling water, bird song or wind rustling through trees, has a direct beneficial effect on our bodies and mental state.

Derrick Taff, from Pennsylvania State University, is conducting an investigation of this phenomenon, so far with 40 volunteers.

In one study, participants were stressed by being asked to make a speech, after which some of them listened to natural sounds − a waterfall, singing birds and wind. Before and after the test their heart rate, emotional state and stress hormone levels were measured.

Compared with listening to no sound, exposure to natural sounds speeded up their recovery from stress.

Another stress test involved asking students to remember random numbers while being distracted. Afterwards they recalled the numbers more quickly when played natural sounds.

“We found that the loudest natural sound condition led to the fastest recovery rate,” Taff told the meeting.

He added: “My biggest advice would be to go to your protected areas and experience what you might be missing.”