Why Current In-the-Ear Hearing Aids Fail

Hearing aids have improved greatly over recent years, but they continue to be a surprisingly frustrating experience for new wearers.

Clearly, today’s hearing aids are tiny, nearly invisible in fact, and they amplify sound and are able to present a higher range of frequencies, but they have not yet completely solved the problem of amplifying the peripheral sounds we just don’t want, or don't need to hear.

For new wearers the crumpling of a paper bag on the other side of a room can sound like a jackhammer.

This is a huge challenge for technology because it is dependent on how the brain perceives sound and how we have learned to filter peripheral sound out of normal hearing. Andrew J. Oxenham is a psychologist and hearing expert at the University of Minnesota and an expert in psychoacoustics.

Oxenham explains: The ear works by analysing sound and breaking it into different frequencies and with many forms of hearing impairment it’s this frequency selectivity that is impaired.

What that means is that the ear doesn’t filter as well as it did before. So instead of having very sharp tuning to filter out different frequencies the filtering becomes much broader and there is no real way of compensating for that.

You can’t sharpen the filters or you can’t pre-process sound so it’s sharp. It’s like a broken TV set. You can process the signal going into the TV as much as you like but you still won’t get a clear picture of the output.

Recent hearing aids have made a lot of progress, like being able to present frequencies of up to 6000 Hz as opposed to limited frequencies up to about 4000 Hz, by using digital signal processing, and a lot more computing power on a lot smaller chip.

Another big leap forward has been made with directional hearing. They can focus the microphones toward the front and filter out a lot of the sound coming from the side and back. And although that is a fairly simple technique, it involves signal processing that wasn’t possible with earlier hearing aids.

Ambient or peripheral sound is horribly distracting for hearing aid wearers. A paper bag being crumpled across a room sounds screechingly loud.

This is common complaint of people who recently start wearing a hearing aid. Their hearing has deteriorated, often without them being completely aware of it, over a period of time.

When they are suddenly fitted with a hearing aid, they hear sounds they’ve got used to not hearing. The sounds are suddenly annoying and distracting. It’s a contrast effect.

It’s more to do with perception i.e the brain’s ability to analyse and prioritise different sounds.

It’s a complex interaction between the ear and the brain. The ear sends signals up to the brain; the brain does an awful lot of processing on top of that; then sends signals back down to the ear. These signals change the way the ear accepts input.

This is partly why hearing aids are not perfect because the hearing aid is not part of that natural feedback loop. There’s no way with current aids that the brain can interface with a hearing aid directly to change its characteristics.

Hearing Loops
To deal with background noise there are things called “hearing loops.”

These are systems that are set up within places like concert halls and churches that interface directly with the hearing aid. It’s like sending a radio signal to the hearing device.

The idea is that this hearing loop picks up the sound directly from the microphone in front of a speaker.

If you are in a conference and the speaker is talking into a microphone. Normally we hear the sound acoustically through the airwaves.

If you are wearing a regular hearing aid the microphone will pick up the sounds on the airwaves but that is together with all the background noise and reverberation in the room.

With a hearing loop it sends the signal directly from the microphone to the ear and bypasses all the acoustics in the building itself. So the ear is getting a much better, clearer and cleaner signal of what’s coming into the microphone.

Two hearing aids better than One?
It’s only recently that people have routinely been fitted with two hearing aids. Often people only got one.

Directional hearing and the way we localise sound: To know where the sound is coming from the brain compares the signals coming into the two ears. So if it’s slightly louder on one side then the brain knows the sound is coming from that side.

More importantly it’s the time of arrival difference between the two ears. If you think about a sound coming from the right. The sound will reach your right ear a little bit before it reaches your left ear.

Although we are talking about millionths of seconds, your brain needs two ears to make a distinction. If you only have one you lose that ability to localise sound and tell which direction it is coming from.

It’s also an important part of filtering out sound and noise. The brain can determine if there is speech right in front and background noise in back of and to the side. The brain can use those differences in localisation to help to make the speech more intelligible.

So the biggest technical challenge is developing hearing aids that can focus on what we really need and want to listen to. This is the current problem.

The Solution
We are hoping through even more sophisticated signal processing schemes that we’ll be able to work on artificial source segregation; i.e. analysing the signal that is coming in and figuring out what is speech and what isn’t, and only presenting to the ear the wanted signal.

Distinguishing between speech and noise
The assumption is that what you really want to listen to is speech, and so there are certain acoustical aspects of speech that we can recognise and there are certain acoustical aspects of noise that are different from speech.

So, we need to establish a suitable algorithm to be able to distinguish between speech and noise that will help you towards filtering the unwanted signal.

A more complete solutiion could mean that brain-computer interface may be part of the hearing aid systems of the future. Where the hearing aid is tapping into brain responses to pick up the specific signal the person wants to pay attention to.

This is an ongoing process with incremental steps and we will continue to see improvements over the next 15 years.

Profound reorganisation in brains of adults who stutter

Hearing Beethoven while reciting Shakespeare can suppress even a King's stutter, as recently illustrated in the movie "The King's Speech."

This dramatic but short-lived effect of hiding the sound of one's own speech indicates that the integration of hearing and motor functions plays some role in the fluency (or dysfluency) of speech.

New research has shown that in adults who have stuttered since childhood, the processes of auditory-motor integration are indeed located in a different part of the brain to those in adults who do not stutter.

The findings are reported in the September 2011 issue of Elsevier's Cortex.

Dr. Nicole Neef and Dr. Martin Sommer from the University of Goettingen, together with Dr. Bettina Pollok from the University of Duesseldorf, studied the performance of a group of adults who stutter, as well as a control group of adults who do not stutter, in a finger tapping exercise.

They used Transcranial Magnetic Stimulation (TMS) to interfere temporarily with brain activity in the dorsolateral premotor cortex while the participants tapped their fingers in time with the clicks of a metronome.

In control subjects, disturbing the left premotor cortex impaired the finger tapping, but disturbing the right premotor cortex had no effect. In stuttering adults, the pattern was reversed: the accuracy of finger tapping was affected by disturbing the right hemisphere, and unaffected when disturbing the left.

Previous research has already linked stuttering with a right-shifted cerebral blood flow in the motor and premotor areas during speech. In this new study, a shift of auditory-motor integration to the right side of the brain occurred even in a task not directly involving speech.

Thus, in the brains of adults who stutter there appears to be a profound reorganisation possibly compensating for subtle white matter disturbances in other parts of the brain -- the left inferior frontal regions. These findings shed light on the extent of the reorganisation of brain functions in persistent developmental stuttering.

Profound reorganization in brains of adults who stutter: Auditory-motor integration located in different part of brain

Fewer Synapses, More Efficient Learning: Molecular Glue Wires the Brain

Yale University researchers have found that a single molecule not only connects brain cells but also changes how we learn. The findings, reported in the December 9 issue of the journal Neuron, may help researchers discover ways to improve memory and could lead to new therapies to correct neurological disorders.

The junctions between brain cells over which nerve pulses pass -- called synapses -- are crucial for regulating learning and memory and how we think. Aberrations in the structure and function of synapses have been linked to mental retardation and autism, while synapses are lost in the aging brains of Alzheimer's patients.

However, the mechanisms that organize synapses in the living brain remain a puzzle. Yale scientists identified one critical piece of this puzzle, a molecule called SynCAM 1 that spans across synaptic junctions.

"We hypothesized that this molecule might promote new synapses in the developing brain, but were surprised that it also impacts the maintenance and function of these structures," said Thomas Biederer, associate professor of molecular biophysics and biochemistry and senior author of the study. "We can now define how this molecule supports the brain's ability to wire itself."

The Yale team focused on SynCAM 1, an adhesion molecule that helps to hold synaptic junctions together. They found that when the SynCAM 1 gene was activated in mice, more synaptic connections formed. Mice without the molecule produced fewer synapses.

When we learn, new synapses can form. However, the strength of synaptic connections also changes during learning, based on the amount of stimuli received -- a quality scientists termed "plasticity." Together with a group in Germany led by Valentin Stein, the team was surprised to find that SynCAM 1 controls an important form of synaptic plasticity.

Unexpectedly, Biederer and colleagues also found that mice with high amounts of SynCAM 1 are unable to learn while mice lacking SynCAM 1 -- and having fewer synapses -- learn better. Apparently an excess of the molecule can be damaging. This builds on recent theories suggesting that having too many connections isn't always better and that the balance of synaptic activity is crucial for proper learning and memory.

"Synapses are dynamic structures. It appears that SynCAM 1 ties synapses together; some of this molecule is needed to promote contact but too much glues down the synapse and inhibits its function. It may act a bit like a sculptor who helps give synapses their shape." Biederer also said that the molecule is almost identical in mice and man, and likely has the same roles in human brains.

Journal Reference:

1. Elissa M. Robbins, Alexander J. Krupp, Karen Perez De Arce, Ananda K. Ghosh, Adam I. Fogel, Antony Boucard, Thomas C. Südhof, Valentin Stein, Thomas Biederer. SynCAM 1 adhesion dynamically regulates synapse number and impacts plasticity and learning. Neuron, 2010; 68 (5): 894-906 DOI: 10.1016/j.neuron.2010.11.003

Brain waves and meditation

Brain waves and meditation

Forget about crystals and candles, and about sitting and breathing in awkward ways. Meditation research explores how the brain works when we refrain from concentration, rumination and intentional thinking. EEG, Electrical brain waves suggest that mental activity during meditation is wakeful and relaxed.

"Given the popularity and effectiveness of meditation as a means of alleviating stress and maintaining good health, there is a pressing need for a rigorous investigation of how it affects brain function," says Professor Jim Lagopoulos of Sydney University, Australia.

Lagopoulos is the principal investigator of a joint study between his university and researchers from the Norwegian University of Science and Technology (NTNU) on changes in electrical brain activity during nondirective meditation.