If you’ve ever felt harassed by something seemingly out of this world, you’re far from alone. However, current research could offer a mundane, if still deeply 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 levels of cortisol, a marker of stress, the researchers found. The study results suggest that hidden sources of infrasound may be the cause of the chills that are often associated with supposedly haunted places, the researchers say.
“It is important to be clear that infrasound does not make people believe they have seen a ghost. What it might do is provide unexplained discomfort, which some people may then attribute to a ghost or ghost,” the study’s lead author, Rodney Schmaltz, a professor of psychology at MacEwan University, told Gizmodo.
The sound of apparitions?
A YouGov poll released Last October (right around Halloween, of course) he found that 60% of Americans believe they have experienced at least one paranormal event in their lives. The most common type of supernatural event, at 35%, was “feeling an unknown presence or energy.”
Many of the stories behind the most famous ghost sightings are full bunk. And some people’s paranormal experiences may illustrate how suggestible our minds are to the mere idea that an old house or a dark basement might contain restless spirits. That said, there seem to be some places in the world where it’s always easy to get the chills. And rather than dismiss all ghosts as a figment of people’s imagination, some scientists have tried to look for answers still based on reality as we know it, including infrasound.
Infrasound is defined as a sound whose frequency is equal to or less than 20 hertz. We cannot normally perceive infrasound, although higher intensity infrasound can still be physically felt as pressure or vibrations. People sometimes report feeling an uneasy feeling about infrasound, and that has led some researchers to study if it could explain some ghosts, although with some mixed results.
Schmaltz and his team have previously investigated the potential effects of infrasound in scary places notable. But this time they recruited 36 participants for a more controlled laboratory experiment. All volunteers were asked to sit in a room while listening to relaxing or spooky music. Half of the volunteers also received infrasound (18 hertz) provided by clandestine subwoofers. Before and after the session, their cortisol levels were measured with a saliva sample and they were surveyed about their mood. After the experiment, they were asked if they felt that infrasound had been played in their room.
Overall, infrasound listeners reported feeling more irritated and more disengaged on average during and after the music session than non-infrasound listeners, while their salivary cortisol levels increased to a greater extent. They also tended to describe any type of music that was played during the experiment as sadder.
“One detail worth noting is that none of this depended on whether people thought the infrasound was activated. When we asked participants at the end of the session if they believed they had been exposed, their answers were no better than guesses, 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, although the findings held up under different sensitivity analyzes (these are used to evaluate how robust the results of a study may be).
At the same time, other studies have supported the idea that infrasound can increase our creepy feeling. In 2002, for example, a famous experiment by psychologist Richard Wiseman and others exposed hundreds of concert-goers in London with silent infrasound notes intertwined with certain songs. Afterwards, people were 22% more likely to report “unusual experiences” like a pit in their stomach during songs that had infrasounds.
The researchers consider their work to be one of the first steps in truly discovering how infrasound can affect the human body, even outside of supposedly haunted houses.
Low frequency sound is common in everyday environments. Ventilation systems, boilers, heavy traffic, large appliances and industrial equipment can generate it,” Schmaltz said. “If modest exposure to infrasound can change our mood in a negative direction and raise cortisol without people realizing it, that has potential relevance to any environment where these sources are present for long periods of time.”
The researchers hope that they or others can conduct larger, more complex studies that better reveal the bodily effects of infrasound. This could involve playing a wide range of low-frequency sounds for longer periods of time, for example, more like real world sources. And they’re already working on another study looking at whether famous haunted locations 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 that their past encounters with the supernatural were not paranormal or entirely in their heads.
“None of this replaces other explanations for the reported apparitions. Expectations and misperceptions play a key role in why a person might report a disturbing experience. That said, infrasound may be another ingredient in the mix,” Schmaltz said. “For people already inclined to interpret a strange feeling as evidence of a presence, it might be enough to tip an ambiguous moment toward a ghostly explanation.”
