It's complicated.

ScienceAlert stories are written, fact-checked, and edited by humans, never generated by AI. Don't miss a story, subscribe here.

Source

On haunted history tours, people often visit eerie theaters and spooky mansions. Such old buildings are often settings for spine-tingling stories. They may also hum with noise too low to hear, from old plumbing or air ducts. That unheard sound, called infrasound, might be one reason these places give people the creeps. A new study hints that even though people can’t hear infrasound, it may influence their mood.

Infrasound is noise with frequencies below 20 hertz — around the lower limit of what humans can hear, says Kale Scatterty. A behavioral neuroscientist, he works at the University of Alberta in Edmonton, Canada. Some natural sources, such as the rumblings of volcanoes and earthquakes, produce infrasound. Traffic, trains, air conditioning systems and other tech also make this low-pitched noise.

Humans and many animals can’t hear infrasound. But past studies have suggested that animals may detect it with their bodies — and that it might even provoke anxiety or fear. Scatterty’s team wondered if people could detect infrasound. Our ears contain otolith organs that help us perceive our movement and position. These organs might pick up on vibrations too low to hear.

Scatterty and his colleagues had 36 people listen to music. Half of them were exposed to infrasound while they listened. The others were not. The scientists then compared the two groups’ responses to the music.

People exposed to infrasound rated music as sadder than those who heard it without infrasound. This was true whether the music itself was calm or unsettling. The infrasound group also said the music was less interesting and reported being more irritable. Cortisol, a stress hormone, was higher in people’s saliva after they experienced infrasound. But people couldn’t seem to tell whether they were in the infrasound group.

The results suggest that infrasound does influence humans’ mood and biology. It seems to happen without people being conscious of it, Scatterty says. The team shared its findings April 27 in Frontiers in Behavioral Neuroscience.

Infrasound might especially affect people and animals near urban environments, Scatterty says. Those places have transit, air conditioning systems and other infrastructure that creates such low-frequency noises. But it’s not clear what the long-term impacts of infrasound exposure might be.

Another open question is whether infrasound provokes fear, he says. In this study, the participants — college students — didn’t report feeling scared or anxious when exposed to infrasound. And the emotional changes the team did measure could have been responses to the study setup. “It could have very well just been that we were priming them to feel something,” Scatterty says. And the students might have felt irritable because they had other places to be.

But a spookier environment might help deepen the investigation. Scatterty and his colleagues have thought about studying infrasound in a haunted house set up for Halloween. “Maybe when you’re in a haunted house, yes, you would react more fearfully because you’re primed to be afraid of something.”

Researchers outfitted two rooms with speakers to play music. Outside of those rooms were two subwoofers — speakers that produce low sounds. In this study, they played infrasound.

The 36 study participants heard either a soothing song that might play at a spa or an eerie tune that would fit in a horror film. Half of the participants heard the music while infrasound played. The team then asked people how the music sounded and how it made them feel.

The researchers compared the answers of those who listened to music with the infrasound off and on (Figures A and B). They also sampled the study participants’ spit to study whether cortisol concentration — a marker of stress — was higher after infrasound exposure (Figure C shows individual measurements as dots and the averages as bars). After answering these questions, participants said whether they thought they had been exposed to infrasound (Figure D).

Data Dive:

1. Look at Figure A. What was the average rating of the calming song as sad when infrasound was off? What about when infrasound was on?
2. Look at Figure B. How irritated were people when infrasound was off versus when it was on?
3. Look at Figure C. What was the average cortisol concentration in spit before people were exposed to infrasound? What was it after?
4. Look at Figure D. What percent of participants correctly guessed whether they’d been exposed to infrasound? What percent were incorrect? How does this compare with what you’d expect if each person guessed by flipping a coin?
5. Cortisol is a marker of stress. What is another event that might be linked to an increase in cortisol levels?

Midden (noun, “MID-den”)

A midden is a garbage pile or dump site left by ancient people. This word also describes a pile of items gathered by an animal.

Old trash heaps can contain artifacts of ancient life. Fossilized scraps from a kitchen dump site can tell us how our ancestors cooked their food. Other sites may contain broken tools, pottery fragments or other clues about people of the past.

Imagine you live in an ancient village along a coastline. You and your people catch food from the sea, especially clams and mussels. You sit at the same site each day to crack open shells and extract the meat. You toss empty shells into the same pile. A thousand years later, an archeologist discovers this shell midden.

From this trash heap, the archeologist might learn more than just what was on your menu. They also might estimate how many people lived in your village and whether you used tools to open shells.

Dump sites containing many shells also create a unique environment that helps preserve fragile materials. Calcium minerals leached from old shells create a low-acid environment. This helps keep bone, fish scales and other biological materials from dissolving. A fragile bone tool, discarded in such a heap, stands a better chance of staying intact.

The word midden also refers to a pile of items collected by an animal. Many rodents create such piles. Squirrels gather and store food in middens. Rats hoard trinkets — such as pieces of trash, beads or seeds — in piles. Many rats even seal their hoards by peeing on them. Rat pee hardens into a shell-like substance called amberat.

Crystallized rat pee repels water and helps preserve the rat’s collection. Throughout human history, rats have lived alongside us. That means that rats may store artifacts from humans in their middens. So, archeologists may study fossilized rat middens for clues about ancient human societies.

In a sentence

Fossilized rat middens can offer a glimpse into the ancient life — not just of rodents, but also of the humans they lived beside.

Check out the full list of Scientists Say.

A cave in Africa seems to host the oldest known traces of humans using fire. Burnt remnants of animal bones hint that groups of Homo erectus used fires here as long as 1.8 million years ago.

The site is known as Wonderwerk Cave. It’s in the Northern Cape province of South Africa. The oldest previously known traces of our early relatives using fire also came from there. Those dated to about 1 million years ago.

The new evidence comes from an earlier, deeper level of sediment in that cave. These traces of fire could be anywhere from 1.07 to 1.79 million years old. But “I’m very comfortable saying it was between 1.7 and 1.8 million years ago,” says Michael Chazan. This archaeologist works at the University of Toronto in Canada. He leads excavations at Wonderwerk Cave.

Chazan was part of a team that shared the new findings June 1 in PLoS One.

The researchers don’t think H. erectus lit the fires. The earliest evidence of people using iron pyrite to make sparks dates to about 400,000 years ago. So people in the Wonderwerk Cave probably carried in flames from wildfires, Chazan says. “This is not human ignition of fire. It’s collecting a fire on the landscape.”

These were likely not cooking fires, but ones used to give light and warmth.

Chazan’s team detected burnt bones at the fire sites with a blue-light technique that forensics experts use to solve crimes. It’s called “luminescence.” Until now, no one had used it in archaeology. The bones came from owl pellets. (Owls cough up such balls of fur and bone after eating.) When examined under blue light, the burned bones glowed more brightly than unburned ones.

Archaeologists already knew that Wonderwerk Cave was probably home to groups of H. erectus at this time. Barn owls also likely sheltered in the cave while these ancient humans lived there, Chazan says. People kept fires going on the pellet-strewn floor. This could explain the finding of burned bones. 

Ancient people didn’t seem to always have fires in Wonderwerk Cave. “There’s a clear signal [of fire],” Chazan says. “But it’s not of year-round access to fire.” Wildfires likely happened only in hot seasons. That may not have been often enough for H. erectus to make any lasting lifestyle changes based on access to flames.