Cochlear Implant-----Nucleus Multi Electrode Implant

[iVenky]

Hello everyone. I know about CIS algorithm involved in Cochlear implantation. I read about Nucleus Multi Electrode Implant (which involves F0/F2 technique) but I couldn't quite understand it. If you could understand it could you please help me? Here's the excerpt----

"The F0/F2 strategy was the first strategy developed for the Nucleus device in the early 1980s. In this strategy, the fundamental frequency (F0) and the second formant (F2) are extracted from the speech signal using zero crossing detectors. One zero-crossing detector is used to estimate F0 from the output of a 270 Hz low-pass filter, and another zero-crossing detector is used to estimate F2 from the output of a 1000-4000 Hz bandpass filter. The amplitude of F2 is estimated with an envelope detector by rectifying and low-pass filtering (at 35 Hz) the bandpassed signal. The F0/F2 processor conveys F2 frequency information by stimulating the appropriate electrode in the 22-electrode array. Voicing Information is conveyed with F0 by stimulated the selected electrode at a rate of F0 pulses/ sec. The amplitude of the pulses is set in proportion to the amplitude of F2. During unvoiced segments (eg: consonant /s/) the selected electrode is stimulated at quasi-random intervals with an average rate of 100 pulses/sec. "




Thank you in advance.

 

[jpanhalt]

These links may help. The first reference is probably closest to your question about Fo and F2. The others are for background. The last (simulator) was for just general interest.

Detailed, see primarily section 1.1 and figure 1:
**broken link removed**

Diagram of how the cochlea distingushes sound:
Cochlear Implant

Much more high level discussion:
**broken link removed**

Cochlear implant simulator:
Cochlear Implant Simulation and Hearing Loss Simulation

John

 

[iVenky]

These links may help. The first reference is probably closest to your question about Fo and F2. The others are for background. The last (simulator) was for just general interest.

Detailed, see primarily section 1.1 and figure 1:
**broken link removed**

Diagram of how the cochlea distingushes sound:
Cochlear Implant

Much more high level discussion:
**broken link removed**

Cochlear implant simulator:
Cochlear Implant Simulation and Hearing Loss Simulation

John

F0/F2 involves two frequencies right? One is the fundamental and other one is the second formant. Then it should be mean that there should be only 2 electrodes right? But we still have many electrodes. That's the reason why I got confused.



Thanks in advance.

 

[jpanhalt]

That is where the second reference comes into play. Multiple electrodes are needed to cover multiple bands. See the hyperlink to "Place Theory." Remember that nerve fibers cannot conduct very high frequencies. Therefore, in the cochlea, it is the location of the stimulated fiber that determines the perceived frequency.

John

 

[iVenky]

That is where the second reference comes into play. Multiple electrodes are needed to cover multiple bands. See the hyperlink to "Place Theory." Remember that nerve fibers cannot conduct very high frequencies. Therefore, in the cochlea, it is the location of the stimulated fiber that determines the perceived frequency.

John

This procedure is for CIS algorithm where we use multiple bands and hence many center frequencies and hence we use multiple electrodes. But in F0/F2 we have only two frequencies- one is the fundamental and the other one is the formant frequency. Hence we have only two frequencies which means that we should be using only two electrodes. But we still have multiple electrodes. That's the reason why I got confused.


Thanks in advance.