Researchers suggested in the Frontiers in Behavioral Neuroscience journal that infrasound, low-frequency sound waves below the range of human hearing, may help explain why certain places feel unusually eerie or unsettling.
"Consider visiting a supposedly haunted building. Your mood shifts, you feel agitated, but you can't see or hear anything unusual," study co-author Rodney Schmaltz, a psychologist at Canada's MacEwan University, said in a statement. "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."
To explore how unconscious sound influences emotions, researchers asked 36 volunteers to sit alone in a room while listening to either calming or unsettling music. During half of the sessions, hidden subwoofers emitted a low-frequency 18 Hz infrasound tone. Afterward, participants completed surveys describing their emotional responses and whether they noticed anything unusual, and they provided saliva samples to measure cortisol levels.
The results showed that cortisol levels were higher when infrasound was present, regardless of whether participants were aware of it. Participants who were exposed to infrasound reported greater irritability and showed higher levels of cortisol. Volunteers also reported feeling more irritable and rated the music as sadder overall. Notably, there was no evidence that participants could reliably detect the infrasound itself.
"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," explained 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."
Because cortisol is closely tied to stress and mood, the findings suggest that even subtle, unconscious stimuli can influence how people feel. However, the researchers caution that their conclusions are preliminary, given the small sample size and focus on a single frequency.
Interestingly, the study adds to growing evidence that environmental factors, such as infrasound generated by old pipes, boilers, or ventilation systems, may shape our emotional responses. In other words, that uneasy feeling in a particular space may not be ghosts, but instead be linked to sound waves we can't consciously hear.
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