A sound that one person hears and the person beside them does not is often treated — by the person experiencing it, and by whoever they tell — as the strangest part of the account, and therefore as the part that demands an exotic explanation. It is the opposite. High-frequency hearing declines with age, steadily and in everyone, and the highest frequencies go first. A tone can sit precisely where one person hears it easily and another, ten years older, hears nothing at all. This is ordinary biology with a name, and it has been built into a commercial product deployed on public streets for two decades. None of this establishes what any particular person has heard. It establishes something narrower and more useful: that this specific feature of an account — that others did not hear it — carries far less weight as evidence than it seems to, and should not be the thing that convinces anyone, in either direction.
- Presbycusis: in 162 adults aged 21 to 70, thresholds at 16 kHz averaged about 25 dB HL at ages 21–30 and 50–55 dB HL from 31 to 60. In the 61–70 group, fewer than one in five responded at 16 kHz and none at 18 kHz.
- The Mosquito, sold since 2005, emits roughly 17.4 kHz for exactly this reason — to be unbearable to younger people and unnoticed by older ones. Deployed on streets in the UK, Canada, Australia, Belgium, France and Ireland.
- The Council of Europe’s Parliamentary Assembly called on governments to ban it in 2010; the UN Committee on the Rights of the Child called on the UK to ban it in 2016. The Home Office declined. No national statutory ban has been enacted anywhere.
- The vendor’s own framing overstates the effect: hearing loss at these frequencies is a continuous slope, not a cutoff at 25.
Open questions
- Is the sound at a frequency a younger person would hear and an older one would not — and were the people who heard nothing older?
- Has anyone tried a recorder capable of the frequency, rather than a second pair of ears?
- If the sound carries words rather than a tone, does presbycusis explain it at all?
References
The third question above is the important one, and this concept does not answer it. Age-related hearing loss explains a tone that some people miss. It does not explain speech.
This concept narrows what one feature of an account can be taken to show. It makes no finding about what anyone has experienced.
Topics: Proposed solutions · Technology · Law enforcement & government · Health & physical effects