March 2017 Blake S Wilson IEEE Pulse
Even as recently as the mid-1980s, many experts in otology and auditory science thought that restoration of useful hearing with crude and pervasive electrical stimulation of the cochlea was a fool’s dream. What the “experts” missed at the time is the brain’s awesome power to process a highly impoverished and otherwise unnatural input and make sense of it. In retrospect, the main task in developing a useful hearing prosthesis for deaf or nearly deaf people was to provide enough information in the right form for the brain to take over and do most of the job. That is not to say that any input would do, as different strategies for stimulation at the periphery produce different results and the initial results were no better than what the experts had predicted. However, once a threshold of quantity and quality of information presented at the periphery was exceeded, the brain could indeed take over and do the rest. Designers needed somehow to exceed the threshold, and that is the story of the modern cochlear implant (CI).
Today, the CI is widely acknowledged as one of the great advances in medicine and something that even the most ardent proponents of CIs could not have foreseen at the beginning. The decades-long path to today included four steps:
- the pioneering step to implant the first patients and develop devices that were safe and could be used for many years in patients’ daily lives
- the development of devices that provide multiple sites of stimulation in the cochlea to take advantage of the tonotopic (frequency) organisation of the cochlea and the auditory pathways in the brain
- the development of processing strategies that utilised these multiple sites far better than before and thereby enabled high levels of speech recognition for the great majority of CI users
- stimulation in addition to that provided by a CI on one side, either with a second CI on the opposite side or with acoustic stimulation for people who have useful residual hearing in one or both ears, usually hearing at low frequencies only.
William F. House contributed the most in achieving the first of these steps and got us started on this great journey. He persisted in the face of the criticisms, and, without that determination, the development of the CI certainly would have been delayed, if initiated at all.
House was a physician and was assisted by Jack Urban, an electrical engineer, in designing and implementing the earliest devices starting in the mid-1960s. House was working at the House Ear Institute in Los Angeles (founded in 1946 by House’s older half-brother Howard), and Urban was president of an aerospace research company in Burbank. This partnership between a physician and an engineer presaged larger teams that included one or more physicians (usually more) and sometimes a goodly number of engineers, plus auditory and speech scientists, audiologists and oftentimes additional professionals. Many teams worldwide participated in those subsequent efforts. The modern CI most certainly could not have been developed without the engineers or the physicians. Such partnerships are, of course, what biomedical engineering is all about.
The approximate times for completion of the steps are shown below, along with the cumulative number of implant recipients between 1957 and December 2012. The dots in the graph show published data points, and an exponential fit to the data has a correlation higher than 0.99. If that exponential growth continues as expected, a million people will have received a CI or bilateral CIs by early 2020; according to unpublished industry records, the number of recipients had already reached a half million in early 2016.
Further improvements in performance were made with adjunctive stimulation (step 4) for people who had enough residual hearing to benefit from combined electric and acoustic stimulation (EAS) and those receiving a second implant. Both combined EAS and bilateral CIs produced statistically significant increases in speech-reception scores, especially for difficult test items or speech presented in competition with noise or other talkers. In addition, bilateral CIs could reinstate at least some sound-localisation abilities, and combined EAS produced large gains in music reception and appreciation. The sound-localisation abilities are no doubt due to representations of the interaural level differences the brain uses to infer the positions of sounds in the horizontal plane, and the better music reception may be due to representations with the acoustic stimulus of the first several harmonics of periodic sounds, as those harmonics are vital for robust perception of fundamental frequencies and thus melodic contours.
Over the past several years, the development of the modern CI has been recognised by many prestigious awards and honours, including the 2013 Lasker–DeBakey Clinical Medical Research Award and the 2015 Fritz J. and Dolores H. Russ Prize, which is the world’s top award in bioengineering and one of three prizes conferred by the U.S.’s National Academy of Engineering popularly known as the “Nobel Prizes for Engineering.” Similarly, the Lasker awards are second only to the Nobel Prize in Physiology or Medicine for recognising advances in medicine and medical science; in fact, more than a third of Lasker laureates go on to win a Nobel Prize at a later time. The engineering and medical prizes for the CI reflect the partnerships that made the CI possible and indicate the importance of the CI to both fields.
The CI is by far the most effective and most utilised neural prosthesis to date. And thus, not surprisingly, it has become the principal model for the development (or further development) of other types of neural prostheses and a foremost exemplar of the power of engineering to improve human health. With respect to the latter point, the design of the CI is included in most every biomedical engineering program worldwide. In addition, it is a core component of the curricula for budding audiologists, auditory scientists, speech scientists, and otologists. But the path to success hasn’t been easy. Joshua Boger, one of the developers of ivacaftor (a drug for the treatment of cystic fibrosis), offers the following cogent and insightful observation about medical breakthroughs, which certainly captures the experience with CIs as well: “The development of ivacaftor was a high-wire act from beginning to end.… If you are looking for dramatic changes in medicine, you are not looking to be comfortable in research; every breakthrough project I know about has passionate detractors”
Some lessons biomedical engineers can learn from the development of the CI are that the experts are not always correct and that perseverance and teamwork are important. Thanks to the second point, most of today’s CI users can communicate fluently via the telephone, even with previously unfamiliar people at the other end and even with unpredictable and changing topics. That wonderful outcome could not have been reasonably imagined at the outset or, indeed, up to the early 1990s when new processing strategies were introduced into clinical practice and the number of implant recipients began to skyrocket. Although room remains for improvement, the present-day devices “allow children to be mainstreamed into regular schools, adults to have a wide range of job opportunities, and for all recipients to connect in new and important ways with their families, friends, and society at large”. The resulting human and economic benefits have been immense—benefits that were made possible by grit, brilliance, key discoveries, exquisite engineering, and multidisciplinary teams.