I was recently reviewing recent advances in cochlear implant (CI) research papers. One of the most comprehensive review papers in the last decade is The Cochlear Implant: historical aspects and future prospects (Jun 2012)¹. In section III. Ongoing research and the future we can read:
Over the past several decades, developments in the field of microelectronics and advances in signal processing techniques not only helped make CIs a reality, but led to increased efficiency and effectiveness of these CI devices in patients.
In this section, the authors describe 3 lines of ongoing and future research:
- Hearing preservation
- Optical stimulation of auditory neurons
- Protection, generation and replacement of neural structures in the cochlea
In the last section, IV conclusive remarks, we can read:
As microchip technology advances at an exponential rate, the size of both internal and external devices is expected to be miniaturized. In addition, advances in directional microphone technology will improve the design of future devices. Combined, the improvements in technology (including laser technology) and utilization of robotic electrode insertion to reduce the electrode insertion trauma and improve surgical accuracy, will achieve the goal of having a completely implantable device with a significant improvement in battery life (Bell et al., 2012). Better speech processing strategies will continue to improve the quality of sound perceived and improve the perception of music by cochlear implant recipients. Furthermore, bilateral implantation using a single internal device and a single processor (Eshraghi et al., 2012) will allow a true binaural stereophonic hearing with excellent sound perception in noise.
From this paper we can — very loosely — trace further published papers in order to see how those trends and lines of research have evolved.
The following are the most recent ones I’ve found.
On the horizon: cochlear implant technology (Oct 2015)²
After a brief historical survey, this review paper describes in more detail the evolving areas of innovation in CI technology as:
- Remote CI programming
- Totally implanted devices
- Improved neural health and survival through targeted drug therapy and delivery
- Intraneural electrode placement
- Electroacoustical stimulation and hybrid Cis
It closes with the following conclusion:
Cochlear implantation and CIs have a long history filled with innovations that have resulted in the high performing devices currently available. There are several promising technologies reviewed above which hold the promise to drive performance even higher.
Cochlear Implantation: an overview (Apr 2019)³
This review paper is the most recent I’ve been able to find. In its closing section, Future Directions, states the following:
From the initial discoveries of auditory stimulation by Alessandro Volta in 1790, to reliably achieving open-set speech recognition with multichannel CI electrodes today, the field of cochlear implantation has advanced at an outstanding rate and the technology is truly nothing short of miraculous. And yet the future may witness continued improvements, from alternative stimulation strategies (e.g., radiofrequency, optical), to robotic electrode insertions with steerable arrays, minimally-invasive mastoidotomy techniques, and drug-eluting electrode arrays to deliver steroids for the prevention of intracochlear scarring or neurotrophic factors to promote neural ingrowth for improved electrode to neuron coupling. In addition to technological progress, improvements in health care delivery and awareness campaigns are needed to bring the benefits of cochlear implantation to more people, both in developed and developing countries. Despite the well-established safety and efficacy of CI surgery, and the fact that it is covered by most public and private health insurance carriers in the U.S., less than 6% of people in the U.S., who could benefit from a CI have one.(35) By raising awareness of the benefits of CI, educating health-care providers on the expanded indications, developing specific referral pathways, established tele-audiology services, and emphasizing the cost-effectiveness of the intervention, improved utilization, and access to this technology can be realized.
Other review papers, for instance Sound Strategies for Hearing Restoration (May 2014)⁴ delve into genome editing and hair cell regeneration through stem cell strategies.
Another citing paper, Electronic Approaches to the Restoration of Sight (Aug 2016)⁵ has an interesting paragraph on the Outlook of sight restoration:
Significant opportunities for improving the implant performance might come from more advanced image processing. Virtual and augmented reality devices are becoming commonplace, and computers are getting better at understanding the features of the visual world. Simplification of the visual scene prior its display on an implant may help better match its resolution and contrast sensitivity limits, and make visual percepts easier to understand. Several groups have already demonstrated promising results by segregating the visual content of a scene by distance, and displaying only the closer objects (176), or by encoding depth instead of luminance information to facilitate navigation (177).
It struck me out that none of the papers reviewing hearing restoration / CI research did mention an engineering or sound-processing approach. The number one challenge currently for CI recipients is understanding speech on a noisy environment.
Cochlear implants are technological marvels. Nevertheless, they work because our brain is a wonderful piece of biological evolution. Brain plasticity makes it possible to “rewire” our memories -our language representation- to the new cochlear electrical stimulation patterns. How can a brain mold itself to still produce musical pleasure after completely cancelling electro-mechanical transduction -involving over 15000 hair cells on a fully functional cochlea- to replace it with the direct electrical stimulation of as few as 24 electrodes ? This is stunning.
Human cochlear hair cells have certain extraordinary properties. One of these properties is the ability to be modulated by the brain. Indeed, this is how we “focus” in noisy environment or balance right and left hearing.
Cancelling electro-mechanical transduction will end this subtle control over sound input (and the preservation of hearing research line mentioned in a few papers above tries to avoid this). For a CI recipient, it is now the role of the sound processor; the external device processing sound and generating arrays of signals sent to the internal device which in turn generates the electrical pulsations. The sound processor runs complex algorithms deciding whose electrodes to pulse and at which frequencies. These algorithms are the outcome of decades of research and development. They were, and still are, developed with human speech understanding as its main priority.
Over the years, new algorithms are developed for different listening situations. Music, noisy environments, and so on. However, the ability to “focus” in noisy environments is unparalleled by current sound processors. Noise and mixed speech in public spaces remain adverse situations for CI recipients.
At this point, one can ask if there are currently technological advances in sound processing which could improve speech discrimination in a noisy environment and if they could be applied to CI technology in the not-so-far future.