A Fine Structure Stimulation Strategy and Related Concepts

The auditory system provides a natural frequency-to-place mapping which is designated as tonotopic organisation of the cochlea. In the normal-hearing system, the acoustic signal causes a fluid pressure wave which propagates into the cochlea. At particular positions within the cochlea, most of the energy of the wave is absorbed causing mechanical oscillations of the basilar membrane. The oscillations are transduced into electrical signals (action potentials) in neurons by the action of the inner hair cells. Waves caused by low input frequencies travel further into the cochlea than those caused by high frequencies. Thus, each position of the basilar membrane can be associated with a particular frequency of the input signal (Greenwood, 1990). This natural form of frequency-to-place mapping, together with the fact that the positioning and fixation of an intrascalar electrode array is comparatively simple, is likely one of the most important factors for the success of cochlear implants as compared to other sensory neural prostheses.