What Is Residual Hearing?

A term that often comes up when discussing hearing and hearing loss is residual hearing. But what is residual hearing? And why is it important?

If someone has sensorineural hearing loss, they can’t hear sounds of certain frequencies below certain volumes. The extent of hearing loss is different for everybody, and having “hearing loss” doesn’t necessarily mean someone can’t hear any sounds. Some people with hearing loss have some remaining hearing, also known as residual hearing.

How Does Residual Hearing Occur?

Hearing is a process in which approximately 20,000 tiny hair cells in the cochlea convert the mechanical vibrations of sound waves into electrical nerve pulses that the brain understands as sound. Sensorineural hearing loss, one of the most common types of hearing loss, occurs when these hair cells are missing or damaged. However, because there are so many of these hair cells, it’s possible that even in cases of profound hearing loss, some hair cells will still be there and working properly.

This is called residual hearing. Intact hair cells can still respond to certain sound frequencies and send sound signals to the brain via the nerve cells. The most common type of residual hearing is low-frequency residual hearing—the ability to hear low sounds even when someone has lost their ability to hear high-frequency sounds. This type of residual hearing is often experienced by older adults. Maybe you or someone you know is unable to hear sounds like birds chirping but can hear sounds like car engines or men’s voices.

Why Is Residual Hearing Important?

Residual hearing is important for everybody with hearing loss because it represents hearing potential.

Individuals who haven’t received a cochlear implant rely on residual hearing to hear. If they have low-frequency residual hearing, they will hear low-frequency sounds best. Hearing aids take advantage of residual hearing by amplifying the sound waves sent to the cochlea so that the remaining hair cells can hear the sounds more easily.

Residual hearing is also important for individuals with a cochlear implant. It is important to preserve their residual hearing so they can still benefit from their remaining natural hearing even after their cochlear implant’s electrode array has been inserted.

This might seem surprising since cochlear implants are designed to replicate the sense of hearing even for individuals with absolutely no residual hearing. But existing residual hearing supports the sounds stimulated by the cochlear implant so recipients can have their best possible hearing.

If someone has enough residual hearing, they may be a candidate for electric acoustic stimulation, or EAS for short. EAS hearing implants are designed for individuals with low-frequency residual hearing. They provide electric stimulation for high-frequency sounds and acoustic amplification for the low-frequency sounds.

How Is Residual Hearing Preserved?

There are two main aspects of residual hearing preservation, also referred to as structure preservation. The first has to do with the design of electrode arrays, and the second is about the surgeon’s technique. The surgical technique is essential, but here we’ll focus on the electrode arrays.

Our electrode arrays are designed to be soft and flexible to preserve the delicate hair cells within the cochlea. Our electrode arrays’ design features unique wave-shaped wires to make them flexible so they can be gently inserted into the cochlea. This helps preserve the hair cells and therefore any residual hearing.

If you’d like to learn more about what an electrode array designed for structure preservation looks like, check out our blog post about the soft and flexible design of MED-EL electrode arrays.