Music & Sound Quality With MED-EL Cochlear Implants, Part 1

In the quest to understand the profound appeal of music and its capacity to evoke deep emotions, researchers faced a complex challenge: translating music into electrical signals for cochlear implant recipients. While these devices excelled at speech comprehension, the enjoyment of music remained elusive, until MED-EL's pioneering approach introduced the Fine Structure Processing (FSP) coding strategy in 2008, revolutionizing music perception and sound quality for implant users.

Music produces a kind of pleasure which human nature cannot do without.

Confucius

What makes music so compelling? How can music make us feel deeper emotions than words?

The answers to these questions lead us to even more questions, such as, “Why is music more difficult to code into electrical pulses than speech?” People with cochlear implants can perform well on speech understanding tests in the sound booth despite poor sound quality, but when it comes to music, sound quality is critical to both understanding and enjoyment.

Decades of cochlear implant research and design improvements steadily improved recipients’ speech understanding scores in quiet and noise. However, the ability to properly code music was a challenging target in cochlear implant development.

Prior to 2008, music perception studies revealed that while recipients did listen to music through their cochlear implants and there were (and still are) individual differences in music preference, poor music listening experiences were a widespread problem.[1]

In general, people reported enjoying music less after implantation than prior to their hearing loss.[2]

Cochlear Implant Recipient Descriptions[3]	Natural Hearing Listeners Descriptions
Unpleasant, something to avoid	Rich
Difficult to follow	Resonant
Scattered	Emotional
Noisy	Delightful
Dull	Stirring
Distorted	Soothing
Harsh	Memorable
Shrill	Pleasant as a background
All the instruments and lyrics blurred together	Desire or excitement to hear a favorite song

MED-EL’s founders initially developed the cochlear implant to improve communication ability, but as they met that goal, they quickly realized good speech understanding was only part of the picture.[4] That’s why they turned their attention to restoring music enjoyment to people with hearing loss.

MED-EL’s Keys to Success

MED-EL’s signal processing researchers wanted to develop a sound coding strategy that could encompass both the envelope and the fine structure.

Early Research
Early work on stimulating the cochlea’s different areas showed that low pitches were represented in the cochlea’s deepest part, known as the apex, and that fine structure cues are related to pulse timing, which are only recognized by that same apical low frequency region.[5][6]
Long Electrode Arrays
MED-EL’s researchers knew they had an advantage. The MED-EL electrode array was the only electrode long enough to potentially reach deep enough into the cochlea and target this low frequency region of the apex.[7][8][9][10]
Free-Fitting Electrode Arrays
Furthermore, MED-EL could accomplish this deep insertion using MED-EL’s flexible free-fitting electrode arrays and without causing additional trauma to the cochlea’s delicate tissues.[11][12][13][14][15][16][17]

MED-EL’s developers had the necessary ingredients, all they needed was the algorithm to make the ingredients work better together, and so they accepted the challenge to bring back music enjoyment to people who listen with cochlear implants.

A Solution to the Music Coding Problem

A significant problem in cochlear implant development existed: cochlear implant recipients were able to score very well on speech understanding tests, in both quiet and noise, even though the sound quality they experienced through their implant was poor, robotic, or cartoon-character-like, and they struggled to enjoy listening to music.

MED-EL is the only cochlear implant manufacturer that has released a new coding strategy since 2008. A coding strategy tells the implant’s audio processor how to analyze the sound coming into the microphone and how to stimulate the implanted electrodes based on that sound. MED-EL introduced the Fine Structure Processing (FSP) coding strategy* in 2008, and further refined the coding strategies (FS4 and FS4-P) introduced in 2014.

Fine structure coding improved speech understanding in both quiet and noise,[18][19][20][21][22][23][24] but the most interesting findings were 1) an improved ability to recognize pitch and 2) the ability to hear and appreciate music.[25][26] Recipients of MED-EL’s fine structure coding strategies said that:

They experienced noticeable changes in their ability to listen to music in just a few weeks with this new coding strategy.
Music sounded pleasant.
Their listening habits changed, where most recipients reported that they enjoyed listening to music more frequently.[27]
Their overall hearing impressions improved, including melody recognition, their ability to distinguish between instruments and singing voices, listening to familiar and unfamiliar music, their ability to identify single instruments in music, and the overall naturalness of sound quality.
They noticed more readily perceivable bass frequency cues and that enhanced music sound quality.

Other studies found that MED-EL implant recipients who used fine structure coding rated sound quality more like the ratings of normal hearing listeners than they did with the previous coding strategy (which did not include fine structure information).[28][29]

These improved results were linked to MED-EL’s philosophy of complete cochlear coverage, which emphasizes using as much of the cochlea as possible by inserting electrodes more deeply so that they can stimulate the cochlea’s apex. Deeply inserted long electrodes better reflected the pitch-based arrangement of the naturally hearing cochlea, and therefore, offered listeners a wider frequency range.[30][31][32]

Today, more natural sound quality has become a reality for MED-EL recipients.

Read the whole story here or read Part 2 now.

Want more information?

Contact your local MED-EL representative or click below!

*Fine structure coding is not indicated for young children in the USA who are in the prelingual period and therefore unable to communicate a preference.

References

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