LONDON (BBC Health News) -- A brain test to detect which frequencies babies cannot hear could help design individualized hearing aids for them, a researcher suggests.

Karolina Kluk, a PhD student at Cambridge University, is developing the test to identify "dead regions" in babies' hearing.

Existing tests, which ask patients to say if they can hear a range of tones or bleeps, cannot be used with babies.

Dr. Kluk will assess the accuracy of her brain test by using it on adults.

Her electrophysiological test checks brainwave responses to different frequencies, played against background noise while the patient is asleep.

The aim is for the test to cover all the frequencies contained in human speech. -------------------Fine-tuning

Hair cells in the cochlea detect sound by vibrating in response to sound waves, triggering nerve impulses that travel to the auditory region of the brain.

Deaf adults and children are often unable to hear sounds at certain frequencies -- high, low or both.

These are known as "dead regions" and represent an area of the inner ear or cochlea where the hearing cells have died off or are not working properly.

Hearing aids work by amplifying the overall amount of sound transmitted into the inner ear. But sound directed towards these dead regions is wasted.

Hearing experts say aids could be more effective if it was possible to work out the precise location of a patient's dead regions, and to then fine-tune the hearing aid so that it only amplified sound to the parts of the cochlea which were still functioning normally. -------------------Implant information

Dr. Kluk has been awarded the Pauline Ashley Prize by the charity Deafness Research UK.

She has now gone to the University of Toronto in Canada to work with Professor Terence Picton in order to compare results from standard hearing tests for adults, compared to the electrophysiological test.

Once results in adults have been compared, and the new test confirmed to be accurate, Dr. Kluk will return to Cambridge and carry out similar tests in children.

She told the BBC News website: "It's important to diagnose 'dead regions' in children as early as possible to be able to fit hearing devices properly or to determine which children require cochlear implants. "In the tests we have carried out on two adult patients, the electrophysiological test does seem to be very reliable."

Dr. Kluk said her research should be complete in around a year, but it would be much longer before any equipment could be put on the market.

Dr. Ralph Holme, biomedical research manager at the RNID, the charity for deaf and hard-of-hearing people, welcomed the research.

He added: "Once it is possible to routinely and accurately diagnose 'dead regions', it will then be important to develop better hearing aid signal processing strategies specifically for people with this type of hearing loss. "RNID is already funding this next step, which will ultimately see children and adults experience better hearing."