Mosquito devices may be used to disperse Australian delinquents—but how do they work?

June 5, 2013 by Catherine Mcmahon, The Conversation
Age-related hearing loss starts a lot earlier than you might think, and is exploited in anti-vandalism measures. Credit: locomomo

You may have read last week that, in a bid to curb graffiti, Sydney's State Rail may trial Mosquito devices – technology that emits a high-pitched noise that's audible only to people aged in their early twenties and younger – to drive away would-be vandals. A kind of teenager repellent, if you will.

Depending on your age, you can hear it, or not hear it, here:

What’s your hearing age?

The same technology has been used widely across Europe since 2006, and especially embraced in the UK, despite calls for it to be banned as it's claimed to violate the ' legislation prohibiting torture.

Ethical aspects aside: how does the Mosquito, and other such devices, target such a specific subset of the population?

As we get older, permanent is affected by as well as the normal (known as presbycusis).

Most commonly, hearing loss occurs in the higher frequencies first, gradually extending to the as the magnitude of hearing loss increases. And it is the in the hearing organ, known as the cochlea (which looks a little bit like a snail shell), which are the most vulnerable to a variety of insults, including

Ear anatomy 101

A sound transmitted through air causes vibration of the that is transmitted to the cochlea via three small bones, known collectively as the ossicles.

This sets up a travelling wave along a membrane in the cochlea, known as the basilar membrane, which progresses from the base of the towards the apex. The properties of the membrane gradually change from the base which is stiffer and narrower (and has less mass) to the apex where it is less stiff and wider (with more mass).

These changes in the membrane's properties cause the membrane to be tuned like a piano (known as tonotopic tuning), where high frequencies are located near the base and low frequencies near the apex.

Credit: Wikimedia

A single row of inner hair cells and three rows of outer hair cells sit on top of this membrane.

These are known as "hair cells" because of the tiny hair-like projections that are located on the top of the cells known as stereocilia. The cells move up and down with the vibration of the basilar membrane and the stereocilia are displaced side-to-side.

Inner hair cells, known as sensory cells, are responsible for the conversion of the basilar membrane vibration into an electrical impulse. Outer hair cells are known as motor cells and "twitch" in time with the vibration of the basilar membrane.

This amplifies the vibration at very discrete areas along the basilar membrane that are related to the frequency of sound presented and provides us with very good frequency discrimination.

We hear when the sound is converted from this mechanical vibration into an electrical impulse which travels up to the auditory part of the brain via the auditory nerve.

Say goodbye to high frequencies

It is the outer hair cells (and, in fact, the stereocilia) which are most physiologically vulnerable to damage. A complete loss of outer hair cells gives a hearing loss of approximately 60 decibels (a moderate hearing loss).

So individuals with a loss of outer hair cells are still able to hear, but usually require amplification from hearing aids to perceive softer sounds in speech.

A cross section of the cochlea. Credit: Wikimedia

The damage or loss of outer hair cells and/or their stereocilia extends from the base, where high frequencies are located, to the apex, where low frequencies are located, creating a typical sloping hearing loss from high-frequency to low.

This decline starts in the late teen years, so it is for this reason that the Mosquito alarm, designed to emit a very high-pitched noise of 17.4kHz, is so annoying to people in their early twenties and younger.

Explore further: Researcher describes cochlear amplification using novel optical technique

Related Stories

Researcher describes cochlear amplification using novel optical technique

December 12, 2012
It has long been known that the inner ear actively amplifies sounds it receives, and that this amplification can be attributed to forces generated by outer hair cells in the cochlea.  How the ear actually accomplishes this, ...

Sensory hair cells regenerated, hearing restored in mammal ear

January 9, 2013
Hearing loss is a significant public health problem affecting close to 50 million people in the United States alone. Sensorineural hearing loss is the most common form and is caused by the loss of sensory hair cells in the ...

Now hear this: Researchers identify forerunners of inner-ear cells that enable hearing

February 26, 2013
Researchers at the Stanford University School of Medicine have identified a group of progenitor cells in the inner ear that can become the sensory hair cells and adjacent supporting cells that enable hearing. Studying these ...

Recommended for you

Best of Last Year—The top Medical Xpress articles of 2017

December 20, 2017
It was a good year for medical research as a team at the German center for Neurodegenerative Diseases, Magdeburg, found that dancing can reverse the signs of aging in the brain. Any exercise helps, the team found, but dancing ...

Pickled in 'cognac', Chopin's heart gives up its secrets

November 26, 2017
The heart of Frederic Chopin, among the world's most cherished musical virtuosos, may finally have given up the cause of his untimely death.

Sugar industry withheld evidence of sucrose's health effects nearly 50 years ago

November 21, 2017
A U.S. sugar industry trade group appears to have pulled the plug on a study that was producing animal evidence linking sucrose to disease nearly 50 years ago, researchers argue in a paper publishing on November 21 in the ...

Female researchers pay more attention to sex and gender in medicine

November 7, 2017
When women participate in a medical research paper, that research is more likely to take into account the differences between the way men and women react to diseases and treatments, according to a new study by Stanford researchers.

Drug therapy from lethal bacteria could reduce kidney transplant rejection

August 3, 2017
An experimental treatment derived from a potentially deadly microorganism may provide lifesaving help for kidney transplant patients, according to an international study led by investigators at Cedars-Sinai.

Exploring the potential of human echolocation

June 25, 2017
People who are visually impaired will often use a cane to feel out their surroundings. With training and practice, people can learn to use the pitch, loudness and timbre of echoes from the cane or other sounds to navigate ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.