Do you also often hear a hum in your ears that others don't? Scientists have found an explanation

Imagine this: you often hear a low-frequency hum, pulsation, or rumbling, the median frequency of which is about 50 hertz. In the English-speaking press, this phenomenon is often simply called "The Hum", and it occurs in 2-4% of people in different parts of the world. 86% of such people report that this sound causes them severe stress and interferes with their lives.

For a long time, two main theories existed in the scientific world regarding what was happening: either these people simply have phenomenal low-frequency hearing and can genuinely hear distant industrial noise, or their inner ear itself generates this sound as a side effect of physiological processes.

To settle this question, a group of scientists led by Boniface Baumann and Markus Drexler (from research centers in Germany and Norway) conducted a detailed study, the results of which were published by the authoritative journal PLOS One.

For the experiment, they selected 28 people who consistently suffer from the hum and compared their metrics with a control group of people with normal hearing. The scientists used ultra-precise equipment for detailed measurement of hearing thresholds in the low-frequency range.

The first hypothesis about "super-hearing", one might say, failed. Scientists performed high-resolution audiometry and found that most people who hear the hum have absolutely normal hearing. Their low-frequency perception thresholds were practically no different from those of the control group.

Among the subjects, two individuals with abnormally high sensitivity were found (their hearing was 20-30 decibels sharper than normal), but for the vast majority, the presence of a real external sound source was not confirmed.

The second hypothesis sounded even more exotic and is called spontaneous otoacoustic emission. This is a real physiological phenomenon where the outer hair cells of the inner ear themselves begin to emit sound waves.

The researchers inserted highly sensitive dual microphones into the ears of the subjects to listen for sounds within their ears, but here too, they were met with disappointment. No low-frequency noise emanating from the patients' ears could be registered. Moreover, it turned out that it is generally impossible to detect such emissions in the human ear at frequencies below 900 hertz.

So what is it then, if not mysticism and not real noise? The authors of the study concluded that in most cases, the mysterious hum is a low-frequency subjective tinnitus — a sensation of ringing in the ears that occurs in a large portion of people and has no external source.

The occurrence of subjective tinnitus is the result of an internal malfunction in the auditory system and is associated with complex interactions at all its levels, from the inner ear and auditory nerve to the auditory cortex of the brain. In such cases, people usually hear a high-pitched squeal, but in reality, this internal sound can take many different forms, including sounding at very low frequencies as a hum or vibration.

And since it is naturally very difficult for humans to determine the sources of low frequencies even with real noises, this auditory system malfunction is automatically masked by the brain. This is why the sound appears to come from outside, rather than from within.

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