Scientists in Canada exposed volunteers to low frequencies of sound that are normally invisible to the human ear, also known as infrasound. The researchers found that compared to control subjects, those exposed to infrasound felt more irritable and experienced higher cortisol levels, an indicator of stress. Researchers say the study results suggest that hidden sources of infrasound may be the cause of the heebie-jeebies associated with allegedly haunted places.
“It’s important to be clear that infrasound does not cause people to believe they have seen a ghost. What it can do is provide vague discomfort, which some people may consider a ghost or being haunted,” senior study author Rodney Schmaltz, professor of psychology at MacEwan University, told Gizmodo.
Ghost voice?
A YouGov survey released last October (around Halloween, of course) 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 a presence or unknown energy.”
Many of the stories behind the most famous ghost sightings are complete nonsense. And the paranormal experiences of some people may reveal how sensitive our minds are to the idea that an old house or dark basement may harbor restless spirits. That said, there are some places in the world where it’s always easier to feel the horror. And rather than dismiss all ghostly talk as a figment of people’s imagination, some scientists have tried to look for answers that are still based in reality as we know it, including infrasound.
Infrasound is defined as sound that has a frequency of 20 Hz or less. We cannot generally perceive infrasound, although high intensity infrasound can still be felt physically as pressure or vibration. People will sometimes report feeling a sense of unease around infrasound, and this has led some researchers to study whether this could explain some ghostly occurrences, although with somewhat mixed results.
Schmaltz and his team have previously investigated the potential effects of infrasound in notable horror locations. But this time, they recruited 36 participants for a more controlled laboratory experiment. All volunteers were asked to sit in a room and listen to either relaxing or scary music. Half of the volunteers were also given a dose of infrasound (18 Hz) provided by secret subwoofers. Before and after the session, their cortisol levels were measured from a saliva sample and they were surveyed about their mood. After the experiment, they were asked whether they thought infrasound was played in their room.
Overall, infrasound listeners felt on average more irritability and more apathy during and after the music session than non-infrasound listeners, while cortisol levels in their saliva increased substantially. He described any type of music played during the experiment as sad.
“One thing 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 effect we saw was not driven by people intentionally 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 acknowledge that the study’s sample size is small, although the findings are subject to different sensitivity analyzes (these are used to measure how robust a study’s results are likely to be).
Additionally, other studies have supported the idea that infrasound can increase our sense of dread. For example, in 2002, a famous experiment by psychologist Richard Wiseman and others exposed hundreds of concertgoers in London to silent notes of infrasound inserted into certain songs. Next, people were 22% more likely to report an “unusual experience” such as a pit in the stomach during infrasound songs.
The researchers consider their work one of the first steps in really finding out how infrasound can affect the human body, even outside of so-called haunted houses.
Low frequency sound is common in everyday settings. Ventilation systems, furnaces, heavy traffic, large appliances and industrial equipment can all produce it,” Schmaltz said. “If minor exposure to infrasound can shift our mood in a negative direction and increase cortisol without people noticing, then this 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 and more complex studies that will better uncover the physiological effects of infrasound. This may involve playing a wide range of low-frequency sounds for a long time, for example, similar to real-world sources. And they’re already working on another study looking at whether famously haunted locations have higher levels of background infrasound than similar non-haunted buildings.
In the meantime, perhaps some people will be consoled by the possibility that their previous experience with the supernatural was neither paranormal nor entirely in their minds.
“None of this replaces other explanations for reported ghostly phenomena. Expectation and misconception play important roles in why someone might report a ghostly experience. That said, infrasound may be another ingredient in the mix,” Schmaltz said. “For those already inclined to interpret this as evidence of the presence of a strange spirit, this may be enough to lead one unexplained moment to a ghostly explanation.”
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