All night long the trains thundered past his building, garbage trucks groaned, and police sirens wailed. In the mornings he was awoken by the sounds of construction: hammers banging, machines drilling, men shouting. He began to wear himself out every night before he got home, studying into the wee hours of the morning or hanging in bars drinking beer until he was ready to drop with exhaustion.

When Cale Holmes moved from Virginia to New York City for grad school, he started to have trouble sleeping.

In 2014, Benfield led a research study to examine whether natural sounds had any impact on participants’ moods. The researchers first evaluated the volunteers’ moods and then deliberately spoiled their moods by showing them disturbing medical videos of hand surgeries. “As we would expect,” Benfield said, “watching medical videos makes people disgusted, negative, and generally in a bad mood.”

Jake Benfield, soundscape researcher and professor of Environmental Psychology at Penn State University, has been studying nature sounds for over a decade. “There is a lot of research that shows that natural views and our visual perception of the environment is good for us, but there is less research about sound,” Benfield told me.

How had the recording helped him so much? Was it that the sound had created a cocoon against the city noises? Or was there more to it? Several teams of researchers around the world have tried to find answers to these very questions.

Holmes had slipped into sleep effortlessly. “And I felt much better about the day the next morning,” he told me. “I felt my sleep was better. I even felt I had more self-esteem.”

The next thing he knew, warm sunlight was filtering in through the curtains. When he checked his laptop, he saw that the recording had paused at just after four minutes when the laptop had powered off.

But one night, Holmes recalled how calm he used to feel whenever he visited a beach. He went to YouTube and ran a search for ocean sounds. Innumerable recordings of ocean waves popped up, some as long as 12 or 14 hours. He selected a nighttime version and let his room fill with the sound of the crashing of waves. He could also hear the wind howl and the cicadas chirp in the distance.

Was there something about the particular frequency of these sounds that caused such a remarkable effect on people’s physiological states? To find out, Benfield explained, researchers at University of Gavle, Sweden, undertook an experiment. They designed an ambiguous, fuzzy sound, which wasn’t entirely discernible, and hence open to interpretation. The researchers then enlisted participants and told half of them that the sound was that of a waterfall while telling the others that it was from an industrial source.

Several other studies conducted in recent years have shown similar results. At Shahed University in Tehran, Iran, a group of researchers found that listening to natural sounds relieved patients in the ICU of their anxiety, while lowering their heart rate and blood pressure. Researchers in Japan’s Osaka City University Medical School found that patients listening to natural sounds showed an improved acceptability to anesthesia, while Johns Hopkins University in Baltimore reported that distraction therapy using nature sounds reduced the amount of pain people experienced during bronchoscopies.

The third group, however, listened to purely natural sounds—like the sound of the wind rustling through trees or the chirping of birds. Participants in this group reported a complete mood recovery.

The researchers then randomly assigned the volunteers to three groups and made them listen to different soundscapes. One group was made to listen to city sounds and traffic. Members of this group reported that their moods became worse. Another group listened to mixed environments containing nature and city sounds, and this group reported no significant mood changes.

What they discovered was that the first group, the one that had thought that the sound was that of running water, showed remarkable mood recovery. On the other hand, the second group that had assumed the sound was unnatural, reported no mood recovery.

Why was it so important, then, for participants to think that they were listening to the sound of water to feel better?

THE 24/7 SENSE

As life evolved on Earth, living beings developed different sensory organs to guide them toward food, alert them to danger, and find their way around the world. Without these senses, we couldn’t have survived. But sometimes, these very senses can cause our minds to get over-stimulated. When there’s too much noise, for example, it can be really distressing, but we usually can’t just turn off our hearing.

From an evolutionary standpoint, this is beneficial to us. If there’s some danger in our environment, we can act accordingly (or wake up, if we happen to be asleep). Sudden sounds jolt us into action, get our hearts pumping, and the adrenaline and cortisol soaring in our bodies so as to prepare us for fight or flight.

But living in a stream of constant, jarring noises can be highly toxic. One of the biggest problems with urban soundscapes, according to Benfield, is that people think they’ve adjusted to them.

“There’s a lot of research showing that the physiological effects of these things‚ sleep disturbances, higher cortisol levels, affect people’s health and cause psychological problems,” he told me.

Living in a stream of constant, jarring noises can be highly toxic

Several studies have pinned mood disorders, anxiety, depression, and even schizophrenia on urban living. Over 82 percent of North Americans live in urban centers, according to a report published by the United Nations in 2014. The global urban population is escalating at an unprecedented rate, creating packed urban conglomerations. Thirty percent of the global population lived in cities in 1950, but this number is predicted to rise to 67 percent by 2050, growing by more than 100 percent in a century, according to the report.

Throughout the course of human evolution, people developed capacities to thrive in natural settings. On the entire span of our evolutionary timeline, urban living is but a mere speck of dust. Although urban living has brought with it many conveniences like access to safety, public health, and other services, it has also created devastating consequences to our physical and mental wellbeing.

But now, the latest research findings show that natural sound can actually help us recover. A study published in March demonstrated that natural sounds have the ability to relieve psychological and physiological stress. Using fMRI and heart-rate monitoring, researchers Gould van Praag, et al, of the University of Sussex found that listening to natural sounds improved parasympathetic activity, whereas listening to artificial sounds prompted sympathetic arousal.

This means that listening to natural sounds promotes our rest and digest state, hence decreasing stress, while listening to artificial sounds promotes the fight or flight response, thereby increasing stress.

THE BIOPHILIA HYPOTHESIS

To understand why this happens, we have to start at the beginning. Nearly 1.5 million years ago, our ancestors picked ripe fruit right off of trees and made love in the mud beneath the canopies. They hiked in groups until they hit the sound of rivers or streams, and settled down with their babies to partake of the fruit of the fertile riverside. The lives of our ancestors were so intertwined with nature that most ancient myths and folklore revolved around nature.

Perhaps this is why birdsong sounds so sweet to the human ear

In those early stages of evolution, certain environments meant survival for the species, Benfield explained. For example, the sounds of rivers, streams, or running water “meant that you would have a chance to survive, by drinking clean, disease free water.” Not only that, but clean water in the environment meant that fruits, nuts and berries would be present too, along with all kinds of animals and biodiversity.