Researchers say infrasound -- low-frequency vibrations from things like pipes, HVAC systems, and traffic that humans can't consciously hear -- may help explain why some old buildings feel unsettling or "haunted." Rodney Schmaltz, senior author and professor at MacEwan, says: "Consider visiting a supposedly haunted building. Your mood shifts, you feel agitated, but you can't see or hear anything unusual. In an old building, there is a good chance that infrasound is present, particularly in basements where aging pipes and ventilation systems produce low-frequency vibrations. If you were told the building was haunted, you might attribute that agitation to something supernatural. In reality, you may simply have been exposed to infrasound." ScienceBlog.com reports: Infrasound sits below roughly 20 Hz, the lower limit of what the human ear can ordinarily detect. It's generated by storms, by volcanic activity, by tectonic rumblings deep in the Earth's crust, and (this is the part that matters) by the mundane mechanical heartbeat of cities: ageing pipes, HVAC systems, traffic, industrial machinery. "Infrasound is pervasive in everyday environments, appearing near ventilation systems, traffic, and industrial machinery," says Schmaltz. Most of the time, we walk through it without a second thought. The question the team wanted to answer was whether walking through it was actually doing something to us, whether the frequency was registered somewhere below consciousness, somewhere we couldn't readily name. The experimental setup was deliberately ordinary. Thirty-six undergraduate students filed one at a time into isolated testing rooms and sat alone with a piece of music, either a calming instrumental or a horror-themed ambient track designed to provoke discomfort. Hidden subwoofers, including a 12-inch unit positioned in an adjacent hallway and a 16-inch speaker oriented toward the ceiling in a neighboring room, pumped infrasound at approximately 18 Hz into half those spaces. The participants had no idea. That last point turned out to be rather important. When the team ran the numbers, they found that participants couldn't reliably identify whether infrasound had been present. Their guesses were, statistically speaking, no better than chance. And according to Schmaltz, participants' beliefs about whether the infrasound was on had no detectable effect on their cortisol or mood. The physiological response didn't care what the participants thought was happening. It just happened anyway. What happened, specifically, was this: those exposed to infrasound reported higher irritability, lower interest in the music, and a tendency to rate the music as sadder, irrespective of whether it was the calming or the horror track. Cortisol levels, measured before and about 20 minutes after exposure, were also elevated. Kale Scatterty, the PhD student who led the work, notes that irritability and cortisol do tend to move together under ordinary stress, but adds that "infrasound exposure had effects on both outcomes that went beyond that natural relationship." That distinction matters more than it might seem. Previous theories about infrasound and paranormal experience have often leaned on anxiety as the explanatory mechanism, the idea that low-frequency sound triggers a kind of free-floating dread that the mind then reaches for supernatural explanations to account for. The new data don't really support that picture. Measures of anxiety didn't budge significantly. What went up was irritability and disinterest, a kind of sour, low-grade aversion rather than fear. That's perhaps a more honest description of how a lot of ghost stories actually feel in the telling: not screaming terror, but wrong atmosphere, a sense of unease that never quite crystallizes into something you can point at. The study has been published this week in Frontiers in Behavioral Neuroscience.Read more of this story at Slashdot.