Although supernatural explanations may seem more exciting, there may be another (real) reason for that shiver down our spine when we enter places that seem scary. It’s called infrasound.
A new study this Monday in Frontiers in Behavioral Neuroscience reveals how the infrassom has a very real impact on human levels of stress and irritability when we are “haunted”.
“In an old building, there is a good chance that infrasound will be present, particularly in basements where aging plumbing and ventilation systems produce low-frequency vibrations. If the building were said to be haunted, you could attribute the shaking to something supernatural. In reality, it may simply have been exposed to infrasound,” explains the research leader. Rodney Schmaltzpsychologist at MacEwan University (Canada), à .
Any sounds below of the threshold from which humans can consciously perceive them – about 20 hertz or less – are infrasound. These sounds have a remarkable ability to cross obstacles without dissipating, which is why their influence is broad.
They can be generated by old plumbing and machinery – hence the connection to haunted buildings – but also from natural sources such as stormsearthquakes, volcanoes and auroras. Some animals even incorporate infrasound into their communication and navigation.
Its ubiquity demands that scientists take infrasound seriously. We’re exposed to it quite frequently, so if certain frequencies do indeed put our bodies into a state of heightened alert, it’s worth investigating any potential long-term consequences.
It was in this sense that the new study recruited 36 university students for an experiment designed to test the effects of infrasound on human stress levels.
As Science Alert details, these participants sat alone in a room, listening to calming or distracting music. For half of these participants, hidden subwoofers also reproduced infrasound at 18 hertz, without their knowledge.
After the session, participants completed a questionnaire about how they felt the music affected them. They also provided saliva samples before and after the session, which researchers used to test levels of cortisol, a biomarker of stress in the human body.
Participants exposed to infrasound reported feeling more irritable, uncomfortable and perceived the music as sadder – even when they had heard the calming music. They were also unable to detect whether subsonic vibrations were present or not.
“The findings suggest that even a brief exposition can change your mood and increase cortisolwhich highlights the importance of understanding how infrasound affects people in real-world contexts”, points out Schmaltz.
As a stress hormone, cortisol is meant to alert us for potential dangers so we can react.
Previous experiments had already suggested that infrasound could have this chilling effect, but what the new study adds is the relationship with cortisol, which increased significantly in the presence of infrasound.
“Increased irritability and higher cortisol levels are naturally related, because when people feel more irritable or stressed, the Cortisol tends to rise as part of the body’s normal response to stress”, said, in turn, the behavioral neuroscientist Kale Scattertyalso cited by Science Alert.
There are theories that some animals react to infrasound from natural events such as earthquakes and tsunamis before a real disaster occurs.
Perhaps there is a similar reason why humans have such negative reactions to infrasound. It could be something we are biologically programmed to avoid for our own safety – scientists theorize.
