Page - 58 - in Cyborg Mind - What Brain–Computer and Mind–Cyberspace Interfaces Mean for Cyberneuroethics

58 • Cyborg Mind Invasive Input Neuronal Interface Systems Neuronal Implants for Deafness A number of different technologies have been, and are continuing to be, developed over the years to address the diminished, or complete lack of, hear- ing function in certain individuals. These have revolutionised the options offered to person who want to regain a better (or even just some) form of hearing. These include: (1) cochlear implants that bypass the dysfunctional signal recognition system in the ear; and (2) auditory brain stem implants that completely sidestep the whole hearing system. Cochlear Implants Cochlear implants have revolutionised the lives of many individuals who were either born with no ability to hear or became deaf after birth. In a healthy hearing system, pressure waves in the air (defined as sound) enter the outer ear and make the tightly stretched fragile membrane, the ear drum, vibrate. A set of three very small bones in what is called the middle ear on the inner side of the eardrum pick up this vibration and mechanically amplify the signal. The last bone in the sequence makes contact with a spiral structure that resembles the outside of a snail shell. Known as the cochlear, this is filled with fluid and lined with millions of hair-like projections. The vibrating bones cause pressure waves to travel through the liquid, thereby deflecting the hairs. In turn, this deflection sets off an electrical impulse that travels along the auditory nerve to an area of the brain known as the auditory cortex. A cochlear implant is used when hearing loss is caused by anything that prevents a signal entering the auditory nerve, but when this nerve remains intact and functional, such as when severe damage exists to the outer or middle ear, or when the hair cells in the cochlear have been lost. The system works by clipping a set of about twenty very small pin-like electrodes around the auditory nerve so that the pins come into contact with the auditory nerve bundle and make close connections with the nerve fibres. A short cable is then connected between the electrodes and a sound microprocessor, containing microphones, which is normally positioned on the outside of the skull behind the user’s ear so that it picks up sound in a similar way to a healthy human ear. In this way, the sound gathered by the microphone is turned into coded signals by the external processor (which selectively filters sound to prioritise audible speech), which is then transmit- ted to the implanted unit that converts them into a set of signals sent to the twenty different electrodes. Accordingly, a cochlear implant works very differently from a conven- tional hearing aid. Instead of simply boosting the sound and blasting it This open access edition has been made available under a CC-BY-NC-ND 4.0 license thanks to the support of Knowledge Unlatched. Not for resale.