Open Access Guide to Audiology and Hearing Aids for Otolaryngologists Cochlear Implants in Developing Countries

The first CIs in the 1960s were singlechannel electrodes; multiple electrodes were introduced in the 1980s in Australia (Figure 1). The basic components of the CI comprise are illustrated in Figure 2: externally worn speech processor (A); a transmitting coil and magnet (B); and surgically implantable receiver/stimulator and electrode (C). Sound is detected by the microphone; a signal is transmitted to the speech processor; the speech processor filters, analyses and digitises the sound into coded signals; coded signals are sent to the transmitter coil via a cable; the transmitter coil sends the code through the skin to the internal implant via radiofrequency signals. The internal implant receiver converts the code to electrical signals; the signals are sent to the electrodes to stimulate the auditory nerve fibres and are recognised by the brain as sounds or hearing. Figure 1: CI device