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The Sound of Metal: Understanding Cochlear Implants


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With awards season recently concluded with the Oscars, one of the films that caught Acentech’s interest was The Sound of Metal. This was a film that had several well-earned Oscar nominations. The main character, Ruben, is a drummer that rapidly loses his hearing. What follows is a heartbreaking exploration of identity, addiction, community, and relationships with deafness and hearing serving as plot motivators.

Background

The Sound of Metal won the Best Sound Category, which was not surprising given the amazing work and attention to detail that went into it. The sound of the movie was an essential storytelling device, bringing the viewer into Ruben’s head to hear through his ears and moving outside of Ruben to hear the world as a typical hearing person would. When Ruben starts to lose his hearing, the high frequencies of sounds he is hearing are turned way down in the soundtrack, similar to how hearing sounds underwater. The sound designers were in fact inspired by the phenomenon of hearing underwater in developing this hearing simulation. Toward the end of the movie, when Ruben is listening through cochlear implants, the sounds are filtered quite differently, to simulate the experience of listening through implants.

The film spends time at a Deaf sober house, as Ruben is dealing with his new deafness while maintaining his sobriety. It is during this time that we see the richness of sign language communication during dinner gatherings, going back and forth between Ruben’s silent perspective and the sounds of the dinner.

Ruben never gives up on the idea of going back to his old life, and jeopardizes his relationship with the Deaf community to do it. He pursues getting cochlear implants, believing that they will make him whole again and will return everything to the way it was before his hearing loss. He sells all of his possessions to pay for the surgery. Once the implants are activated, he is surprised that hearing through the implants (also known as electric hearing) sounds much different than the acoustic hearing he experienced for most of his life. In the simulated sounds of the film, voices sound distorted and it is difficult to pick out one voice when several people are talking.

The movie uses his sudden realization that the implants and the results of his choices don’t magically return his hearing to the way it was as a powerful plot device. However, in real life, he never would have been offered the surgery without extensive education on the benefits and drawbacks of cochlear implants and a discussion that hearing with implants sounds a lot different than acoustic hearing. Also, extensive post-surgery rehab treatments would have been recommended for Ruben to help him get accustomed to the hearing from his implants.

Understanding Cochlear Implants

Cochlear implants are marvels of biomedical engineering that partially restore hearing to people that have lost their hearing and others that were born deaf. Deciding whether to get these implants is a deeply personal choice made by individuals and their families that is controversial to some in the Deaf community. Those that receive implants gain back a lost sense and experience a method of communication that they either never experienced or thought they would never have again. However, as discussed above, hearing with cochlear implants is much different than typical hearing.

In typical acoustic hearing, sound arrives at the ears and is transmitted into the inner ear where the sound is transformed into nerve signals by inner hair cells. When these hair cells no longer function, cochlear implants can be used to stimulate the nerves that are connected to the hair cells. The cochlea is a small snail shell-shaped organ in the inner ear; it is laid out with areas of different frequency sensitivity with the base responding to high frequencies and the apex responding to low frequencies. The cochlear implant is a small wire that is carefully threaded up through the turns of this snail shell shape. This wire has several electrodes along its length to stimulate nerves corresponding to different frequencies. Because the fluid that fills the cochlea is a conductive fluid essentially like salt water, the electrodes not only stimulate the nerves near them but nerves up and down the cochlea due to current spread. The result of this current spreading is reduced frequency selectivity, meaning that fewer pitches can be perceived.

With acoustic hearing, the cochlea is able to reject some noise, which helps the listener to understand speech in noise. In acoustic hearing, with our ears, sound that arrives at different directions is filtered differently by the folds and ridges of our outer ears, and that filtering helps us tell what direction sounds are coming from. In electric hearing sounds arrive at the cochlear implant microphone without this filtering. Also, sounds arrive at the two ears at different times, and cochlear implant wearers are not as able to use this cue to help determine the location of sound sources and to distinguish particular sound sources.

Acoustically Appropriate Spaces for Cochlear Implants

These cochlear implant limitations affect the suitability of spaces for implant wearers. Lower background sound levels and reverberation are more important for cochlear implant wearers to understand speech than those with typical hearing. There are no standards for spaces for adults with cochlear implants like Ruben, but we can be inspired by requirements developed for classrooms for children.

The ANSI S12.60 classroom acoustics standard was written to help all students, including those with hearing impairments, to be able to understand speech in their learning environments. In most classrooms, this standard calls for background noise levels no greater than 35 dBA and reverberation times no greater than 0.6 seconds (in mid frequencies). The standard calls for classrooms to be readily adaptable to reduce the reverberation time down to 0.3 seconds with the addition of more sound absorptive surfaces and states that this shorter reverberation time “is necessary for children with hearing impairment and/or other communicative issues.” Iglehart (2016) found that reducing the classroom reverberation time to 0.3 seconds provided an appreciable benefit for children with cochlear implants. We are able to review existing spaces and spaces in design to determine what sound absorption is necessary to achieve low reverberation times.

Ruben’s journey is not typical for cochlear implant wearers, but it fit the narrative of the story. With counseling before surgery, extensive rehab after surgery, and acoustically appropriate spaces, those who choose to receive cochlear implants can experience the sense of hearing.