In a recent study, researchers found that infrasound can still affect humans even though we cannot consciously hear it. This research may help explain how the environment affects cortisol levels.
Infrasound is defined as low-frequency sound waves below 20 hertz. These vibrations can occur in storms, traffic and industrial equipment. Some species rely on infrasound as a form of communication.
The study suggests that infrasound can increase our cortisol levels and shift our moods, potentially explaining why some people feel unsettled in places such as cities or abandoned buildings.
“Many people are exposed to it without knowing it,” Rodney Schmaltz, a professor at MacEwan University, told Science News.
Every participant was exposed to one musical stimulus. They were either in the infrasound group or the one where it was not present.
Those in the infrasound group were exposed to subwoofers for approximately four minutes and 40 seconds during a five-minute music clip, allowing time for the subwoofer to be turned on and off at the beginning and end.
After listening, they completed a 20 item Positive and Negative Affect Schedule, using a 5-point scale ranging from “very slightly” to “extremely” to rate their feelings.
They were also asked to rate the music and if they thought they were exposed to the subwoofers.
PANAS and self-reported measures showed that participants exposed to the infrasound didn’t enjoy the music and described it as sad.
They also reported feelings of guilt and irritability.
Regardless of the infrasound, the reports showed that calming music increased positive effects while unsettling music increased negative ones.
“This study suggests that the body can respond to infrasound even when we can’t consciously hear it,” Schmaltz said. “Participants 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.”
Saliva samples were taken before and after testing to measure cortisol levels. Researchers found that cortisol levels increased in participants exposed to infrasound. They reported feeling less interested and more irritable after listening.
Although the results did reveal an impact, the sample size was small and did not account for how infrasound interacts with other frequencies in an environment. Since the study focused on infrasound alone, it is not clear if it can increase cortisol levels in combination with other frequencies humans are exposed to every day.
The study also focused on participants who showed no signs of a condition that would impact their hearing, nor did it account for how well each person can hear. To further understand how infrasound plays a role in cortisol levels, a larger and more diverse range of individuals could be included.
