Of all afflictions, one of the most infuriating is tinnitus. Just about everyone gets a bit of tinnitus occasionally, and it can be a problem for 10-15 per cent of the adult population. For some, it's intrusive enough to interfere with daily life, leading to depression.
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Tinnitus can be experienced in a few ways, including whooshing, clicking, buzzing, hissing or roaring sounds.
The strange thing is, these sounds are usually generated entirely within our heads rather than from an external source. However, there is a form called "objective tinnitus" which can be detected by a microphone. This is caused by the blood vessels, muscles or the bones in your ear.
Subjective tinnitus is more common. Its cause tells us something about how nature has evolved the remarkably sophisticated system that is our hearing.
On one hand, good ears can detect sounds as a quiet as a single decibel, which may indicate prey - or a predator - nearby.
On the other hand, it must cope with extremely loud sounds such as heavy machinery or earbuds turned up too far. A shotgun can produce 165 dB and, since the decibel scale is logarithmic, that is an enormous difference in amplitude. It is a huge challenge for a system to work over such a range.
Fortunately, your hearing has a few tricks. One of these is how the brain processes information. Cells in the dorsal cochlear nucleus act as a kind of variable amplifier.
In noisy situations it "turns the volume down" and, in quiet ones, boosts it.
When things get really quiet, hearing sensitivity is at its greatest and tinnitus becomes like the brain listening to its own noise.
Tinnitus is usually triggered by a drop in perceived volume, which may indicate hearing loss. Or it can occur after exposure to excessive noise such as machinery or live music. This is a warning because it can indicate permanent damage to your hearing.
Curiously, tinnitus is often experienced as pure tones.
To get an idea of what's happening, search online for "synchronised metronome". In one video, you'll see 32 metronomes on a table, suspended by strings on each corner. The metronomes begin clack-clacking in a chaotic dance. But then order emerges as each metronome gradually falls into step with the others. It is something like this synchronisation that produces a pure tone.
The strangest cases are people who hear phantom music. This might be trumpet sounds, original "compositions" or, in the most florid cases, lengthier sections of known music.
In a future column we will tackle whether there is a cure. If you need help, contact your local branch of Better Hearing Australia.
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