How cochlear implants have expanded our understanding of speech perception

The design of cochlear implants has developed rapidly in recent years, and there are now numerous adults and children with sensorineural deafness who receive highly intelligible speech signals through these devices. Research into speech perception and implant design has identified several principles that seem to be essential to achieve adequate performance with an implant. These include: (1) control of electric stimulation levels to encode acoustic intensities appropriately, within a comfortable range of loudness; (2) stimulation with brief pulses delivered non-simultaneously to the electrodes, to avoid unwanted interactions; (3) use of stimulation rates high enough to represent temporal features of signals accurately; and (4) provision of at least seven active electrodes to enable adequate representation of spectral features. There are advantages in providing more electrodes, probably up to at least the 22 intracochlear electrodes presently available in the prosthesis manufactured by Cochlear Limited. Research is continuing to improve the design of the sound processors used with cochlear implants. This is expected to enable better speech intelligibility in noisy listening conditions, and better perception of nonspeech sounds, including music