Single Channel versus Multi-Channel Cochlear Implants
Many people think of ''channels'' in cochlear implant systems as the number of ''electrode contacts.'' While the two terms are sometimes used interchangeably, this practice does not accurately define either term. In cochlear implant systems, the term channel refers to the number of stimulation sites within the inner ear, or cochlea, and is defined by a range of frequencies, or pitches. All sounds, ranging from low pitch (bass) to high pitch (treble) sounds are separated into the number of available channels.
In a single channel system, all sound information is delivered to only one channel. Thus, all information is transmitted to a single area of stimulation within the cochlea, regardless of the pitch of the incoming signal.
Multi-channel cochlear implant systems divide the incoming signal into various frequency bands that are then transmitted to various sites of stimulation spanning the inner ear. In this way, low pitch sounds are sent to one part of the cochlea and high pitch sounds to another. The goal in multi-channel systems is to more closely mimic the human ear, in which sounds are organized by frequency, like the keys of a piano. Because the system can transmit much more detailed information about the incoming signal, the processing of sound is more complex, and the device fitting is somewhat more involved.
The general belief is that multiple channels provide a more detailed representation of sound and, therefore, better speech understanding than just one channel is capable of transmitting. There is still some debate on how many channels are needed, and there is clearly no ''magic number.'' Independent researchers tend to agree that speech understanding is not greatly improved with more than 6-10 channels. Speech understanding with multi-channel implant systems tends to decline when fewer than four channels are used.