If you’ve ever felt stalked by something seemingly not-of-this-world, you’re far from alone. Research out today, however, might offer a mundane, if still profoundly creepy, explanation for some of these encounters with the supernatural.
Scientists in Canada exposed volunteers to low frequencies of sound normally imperceptible to the human ear, also known as infrasound. Compared to control subjects, people exposed to infrasound reported feeling more irritable and experienced higher cortisol levels, a marker of stress, the researchers found. The study’s results suggest that hidden sources of infrasound can be a cause of the heebie-jeebies often linked to reportedly haunted places, the researchers say.
“It is important to be clear that infrasound does not cause people to believe they have seen a ghost. What it might do is provide unexplainable discomfort, which some people may then attribute to a ghost or haunting,” senior study author Rodney Schmaltz, a professor of psychology at MacEwan University, told Gizmodo.
The sound of hauntings?
A YouGov poll released last October (right around Halloween, of course) found that 60% of Americans believe they’ve experienced at least one paranormal event in their lives. The most common kind of otherworldly event, at 35%, was “feeling a presence or unknown energy.”
Many of the backstories behind the most famous ghost sightings are complete bunk. And some people’s paranormal experiences might only illustrate how suggestible our minds are to the mere idea that an old house or dark basement could contain restless spirits. That said, there do seem to be some places in the world where it’s consistently easy to feel the creeps. And rather than dismiss all hauntings as a figment of people’s imagination, some scientists have tried to look for answers still grounded in reality as we know it, including infrasound.
Infrasound is defined as sound that’s at or below 20 hertz in frequency. We normally can’t perceive infrasound, though higher-intensity infrasound can still be felt physically as pressure or vibrations. People will sometimes report feeling a sense of unease around infrasound, and that’s led some researchers to study whether it might explain some hauntings, though with some mixed results.
Schmaltz and his team have previously investigated the potential effects of infrasound in notable scary locations. But this time, they recruited 36 participants for a more controlled lab experiment. All of the volunteers were told to sit in a room while listening to either relaxing or creepy music. Half of the volunteers were also dosed with infrasound (18 hertz) provided by clandestine subwoofers. Before and after the session, they had their cortisol levels measured with a saliva sample and were surveyed about their mood. After the experiment, they were asked if they felt infrasound had been played in their room.
All in all, the infrasound listeners reported feeling more irritated and more disinterested on average during and after the music session than the non-infrasound listeners, while their salivary cortisol levels rose to a greater extent. They also tended to describe either kind of music that was playing during the experiment as sadder.
“One detail worth noting is that none of this depended on whether people thought the infrasound was on. When we asked participants at the end of the session whether they believed they had been exposed, their answers were no better than guessing, and their beliefs did not predict their mood or cortisol responses,” Schmaltz said. “So the effects we saw were not driven by people consciously noticing the stimulus and reacting to it.”
The team’s findings were published Monday in the journal Frontiers in Behavioral Neuroscience.
What happens next?
The researchers admit that the study’s sample size is small, though the findings did hold up under different sensitivity analyses (these are used to gauge how robust a study’s results are likely to be).
At the same time, other studies have supported the idea that infrasound can ramp up our creepy sense. In 2002, for instance, a famous experiment by psychologist Richard Wiseman and others exposed hundreds of concertgoers in London to silent notes of infrasound laced into certain songs. Afterward, people were 22% more likely to report “unusual experiences” like a pit in the stomach during the songs that had infrasound.
The researchers consider their work to be one of the first steps in truly figuring out how infrasound can affect the human body, even outside of purportedly haunted houses.
Low-frequency sound is common in everyday settings. Ventilation systems, furnaces, heavy traffic, large appliances, and industrial equipment can all generate it,” Schmaltz said. “If modest exposure to infrasound can move our mood in a negative direction and elevate cortisol without people noticing, that has potential relevance for any environment where these sources are present for long stretches of time.”
The researchers hope that they or others can conduct larger and more complex studies that better tease out the bodily effects of infrasound. This might involve playing a wide range of low-frequency sounds for longer periods of time, for instance, more akin to real-world sources. And they’re already working on another study looking at whether famous haunted places tend to have higher levels of background infrasound than similar non-haunted buildings.
In the meantime, perhaps some people will take solace in the possibility their past run-ins with the supernatural were neither paranormal nor entirely in their heads.
“None of this replaces other explanations for reported hauntings. Expectation and misperception play a key role in why a person might report a haunting experience. That said, infrasound may be one more ingredient in the mix,” said Schmaltz. “For people who are already inclined to interpret a strange feeling as evidence of a presence, it could be enough to tip an ambiguous moment toward a ghostly explanation.”
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