The present invention relates generally to auditory prostheses and signal generators for auditory prostheses. More particularly, the present invention relates to such signal processors employing a plurality of band pass filters.
Various types of multichannel auditory prosthetic devices exist in the art.
One example of a multichannel auditory prosthesis is described in U.S. Pat. No. 4,400,590, Michelson. Michelson discloses a system that uses the theory that differing places along the cochlea respond as differing frequencies to the brain. Thus, band pass filters break up the incoming auditory signal into a plurality of frequency bands. These signals are than applied directly to electrode locations along the cochlea. In theory those locations which correspond its associated frequency band.
Another example of a multichannel auditory prosthetic device, is described in U.S. Pat. Nos. 4,289,935, Zollner et al and 4,403,118, Zollner et al. The system debcribed in the Zollner et al patents uses a set of band pass filters to generate frequency bands to turn on and off, or to modulate, oscillators (tone generators) whose outputs are then summed and transmitted to a hearing aid.
Both of the Michelson and Zollner et al multichannel auditory prosthetic devices, however, have been less than completely successful in obtaining open set speech comprehension without the use of visual aids;
Young and Sachs, in a 1979 article, "Representation of Steady-State Vowels in the Temporal Aspects of the Discharge Patterns of Auditory Nerve Fibers", 66 Journal of the Acoustic Society of America, pp 1381-1403, noted that spectral information is represented in the timing patterns of auditory nerve discharges. They determined the energy at a given frequency by examining temporal responses only among neurons whose center frequencies were close to that frequency.