12From hearing aid to implant
The chapter has traced, deficit by deficit, why amplification eventually falls short of the damaged cochlea — and every thread leads to the same resolution. A hearing aid is an acoustic device: it makes sound louder and sends it through the ear's own machinery, the very machinery that recruitment, blurred resolution and dead regions have broken. A cochlear implant is an electrical device: it converts sound into current and stimulates the auditory nerve directly, skipping the broken cochlea entirely. Free of recruitment, able to drive a wider and steadier range straight to the nerve, it delivers a cleaner signal that the brain can learn to hear. That single structural difference — working around the cochlea rather than through it — is why, past the crossover, the implant succeeds where the aid cannot. This closing module draws the threads together and opens the door to candidacy.
FThrough the cochlea, or around it
The deepest difference between the two devices is structural. A hearing aid amplifies sound and delivers it through the cochlea — so it is hostage to whatever has damaged the cochlea. A cochlear implant converts sound to electrical pulses and stimulates the nerve directly, going around the broken organ. The aid depends on the failing machinery; the implant replaces it.
TWhat changes when you bypass it
Bypassing the cochlea undoes, at a stroke, the deficits the chapter described. Because the implant drives the nerve directly, there is no recruitment (the neural response grows linearly), the usable range is wider, and the place and timing of stimulation are imposed by the processor rather than left to broken filters and dead regions. On activation, recipients hear softer sounds over a wider frequency range than a hearing aid ever gave them — typically reaching aided levels around 25–35 dB through 8 kHz — and, across studies, good speech recognition even at soft input levels.[2004]
CNo longer a last resort
For this reason the cochlear implant is no longer a last resort. With safer surgery, better processing, and proven outcomes, candidacy criteria have relaxed and the implant has become the treatment of choice for severe-to-profound sensorineural hearing loss. Its benefits run from sound awareness to open-set speech, the telephone, music, and speech in noise, with gains in education, employment and quality of life. Like the hearing aid, it does not perfectly reproduce natural hearing — but with training most recipients describe their implant as clearer, sharper and more comfortable than the aids it replaced.
TInto candidacy
This chapter answered why a hearing aid stops being enough. The next answers who should therefore be implanted, and how that is decided: the audiological and medical candidacy and evaluation of Chapter 11. The question this chapter hands forward is the one a candidacy clinic exists to settle — has amplification truly done all it can, and does this patient sit past the crossover?
What is the key difference that lets the implant succeed?
What is the fundamental difference that lets the implant succeed where the aid fails?
Which statement best reflects the modern status of the cochlear implant for severe-to-profound SNHL?