![\"Scatterty](\"https:\/\/cdn.sci.news\/images\/enlarge13\/image_14724e-Infrasound.jpg\")
<\/a><\/p>\nScatterty et al. used a combination of self-report and biological measures to demonstrate that infrasound can have irritant, and aversive properties on humans. Similarly, infrasound appears to influence increases in negative affective evaluation.<\/p>\n
Infrasound can be defined acoustically as soundwaves with an upper frequency limit below 20\u202fHz.<\/p>\n
It can occur naturally, generated, for example, by tectonic or volcanic activity, convective storms, and air-water interactions such as during upstream water discharges.<\/p>\n
Infrasound is also, however, prevalent in urban areas near ventilation systems, air conditioning, low-rumbling pipes, traffic and building power, heating, mechanical systems.<\/p>\n
Exploratory field recordings also detected low-frequency acoustic energy in the infrasound range from similar urban sources as well as during musical performances.<\/p>\n
\u201cInfrasound is pervasive in everyday environments, appearing near ventilation systems, traffic, and industrial machinery,\u201d said MacEwan University\u2019s Professor Rodney Schmaltz.<\/p>\n
\u201cMany people are exposed to it without knowing it. Our findings suggest that even a brief exposure may shift mood and raise cortisol, which highlights the importance of understanding how infrasound affects people in real-world settings.\u201d<\/p>\n
For their study, the authors recruited 36 participants and invited them to sit alone in a room while either calming or unsettling music was played.<\/p>\n
For half the participants, hidden subwoofers played infrasound at 18 Hz. After listening, they were asked to report their feelings, their emotional rating of the music, and whether they thought the infrasound was present. They also gave saliva samples before and after listening.<\/p>\n
The researchers found that participants\u2019 salivary cortisol levels were higher if they had been listening to infrasound.<\/p>\n
These participants also reported feeling more irritable and less interested, and thinking the music was sadder. But they couldn\u2019t tell they were listening to infrasound.<\/p>\n
\u201cThis study suggests that the body can respond to infrasound even when we can\u2019t consciously hear it,\u201d Professor Schmaltz.<\/p>\n
\u201cParticipants could not reliably identify whether infrasound was present, and their beliefs about whether it was on had no detectable effect on their cortisol or mood.\u201d<\/p>\n
\u201cIncreased irritability and higher cortisol are naturally related, because when people feel more irritated or stressed, cortisol tends to rise as part of the body\u2019s normal stress response,\u201d said Kale Scatterty, a Ph.D. student at the University of Alberta.<\/p>\n
\u201cBut infrasound exposure had effects on both outcomes that went beyond that natural relationship.\u201d<\/p>\n
These results indicate that humans can sense but not identify infrasound, though the mechanism remains unclear.<\/p>\n
They also suggest we may need to investigate whether prolonged infrasound exposure could impact health through consistently elevated cortisol levels and wellbeing issues related to lowered mood and increased irritability.<\/p>\n
\u201cIncreased cortisol levels help the body respond to immediate stressors by inducing a state of vigilance,\u201d said MacEwan University\u2019s Professor Trevor Hamilton.<\/p>\n
\u201cThis is an evolutionarily-adapted response that helps us in many situations. However, prolonged cortisol release is not a good thing. It can lead to a variety of physiological conditions and alter mental health.\u201d<\/p>\n