Humans Hear the Unheard: New Study Explains Infrasound Perception

A research team led by Torsten Marquardt of University College London and Carlos Jurado of the Norwegian University of Science and Technology published new findings in *Scientific Reports* that clarify how humans detect infrasound—sound below about 16 Hz, traditionally considered outside the audible range. The study shows that, when low-frequency waves strike the ear, outer hair cells generate electric fields strong enough to trigger nerve signals, allowing the brain to register the stimulus even though it does not produce a conventional tonal perception.

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The mammalian inner ear contains two hair-cell types. Inner hair cells normally convey tonal information to the auditory nerve. At very low frequencies, the signal from these cells becomes too weak. The researchers found that outer (support) hair cells, which usually modulate hearing sensitivity, can directly convert sub-20 Hz vibrations into electric impulses. These impulses travel to surrounding nerves, bypassing the standard pathway and producing a sensation that feels more like vibration or pressure than a clear tone.

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Because the outer-hair-cell pathway may differ among people, sensitivity to infrasound is highly individual. The phenomenon helps explain why some individuals report unease in “spooky” buildings or react strongly to low-frequency noise from HVAC systems, generators, or traffic, while others remain unaware. Prior work linked infrasound exposure to elevated cortisol levels and irritability, suggesting a physiological response beyond conscious hearing.

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The authors conclude that the discovery resolves a long-standing puzzle about the gradual decline of hearing sensitivity into the infrasonic range and provides a natural explanation for the distinct, often unsettling quality of low-frequency noise. They note that the findings could inform building design, occupational health standards, and future research on how subtle acoustic cues influence human emotion and physiology.

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• “These support cells, which normally receive signals from the brain to regulate hearing sensitivity, generate electric fields that are strong enough to trigger nerve signals that are sent to the brain, so that infrasound is perceived.” — Torsten Marquardt, study author, University College London

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• “Humans can actually perceive infrasound if the sound level is high enough,” — Carlos Jurado, Norwegian University of Science and Technology

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• “Other hair cells, which normally contribute to the hearing process, can still pick them up,” — Carlos Jurado, NTNU

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• “This may explain why infrasound is experienced differently than normal sound. Small increases in sound pressure quickly make the sound much louder. We can now easily explain this phenomenon as a natural consequence of our new findings,” — Carlos Jurado, NTNU

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