Cochlear implant
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Hello. I want to know a lot about CIS algorithm that is used in cochlear implantation. If you could provide me any link related to that I would be happy. I would also like to know the code/ algorithm for Cochlear implantation tool in the Matlab.
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Daniel Shub
2012-1-8
Venky, it is much easier to contrbute if you make comments to the corresponding answer, edit your question where approriate and aske new questions when needed. You should also consider voting for answers that you think are helpful. This lets people know if they are on the right path.
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Wayne King
2012-1-7
Hi, You can read a nice introduction to the continuous interleaved sampling approach here
The DSP System Toolbox has a Simulink-based demo of a CIS algorithm in dspcochlear.mdl
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Wayne King
2012-1-7
I should say that the demo is missing the nonlinear compression that is typical in cochlear implants. The nonlinear compression is necessary because the tolerable dynamic range of electrical stimulation for patients (the difference between threshold and uncomfortable) is usually pretty small.
Daniel Shub
2012-1-8
Not sure where this should go. There are many different strategies for cochlear implant processing. I believe the two that are currently in use on new devices are CIS and SPEAK, with SPEAK begin used by Nucleus.
The F0/F2 is not CIS. At any one moment there are only two frequencies/features be provided to the user. These however rapidly change. If I recall correctly, F0 was encoded by the pulse rate and F2 by the electrode #. I think there may have been a loudness component coded by the amplitude of the pulses. One of the advantages of this approach is that only 1 electrode is active at any time.
For CIS all the electrodes, or a pre determined subset of them, are active. Each presents a pulse in sequence. The rate of the pulses and the pulse shape are fixed. The amplitude of the pulse train is modulated to provided information. Basically, the sound is split into a number of bands ~8-16 and the envelope is extracted. The bandpass filters and envelope extraction properties are usually proprietary. Researchers tend to use either halfwave rectification and low pass filtering or the Hilbert transform to get the envelope. Normal hearing models of CIS processing have been developed. There is a paper by Shannon (Science 1995) and another by Smith (Nature 2002) which present some interesting idea.
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Daniel Shub
2012-1-8
You are confusing F0/F2 with CIS. In CIS there are generally the same number of filters as there are electrodes. There are no zero-crossing detectors in CIS. The pulse rate in CIS is fixed. The output of each bandpass filter is feed to an evelope detector. The output of the envelope detector is used to modulate the pulse train.
i Venky
2012-1-8
2 个评论
Wayne King
2012-1-8
Hi, .mdl is a Simulink model file. It is part of the DSP System Toolbox. If you search "Cochlear Implant Speech Processor" you will find it.
i Venky
2012-1-8
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Wayne King
2012-1-8
Hi, all cochlear implant techniques for speech proceed from a desire to answer the question: what is the minimally sufficient information for speech understanding? The F0/F2 technique extracts the fundamental frequency envelope (amplitude modulation) and the second formant envelope (amplitude modulation) as important for speech understanding.
i Venky
2012-1-8
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Wayne King
2012-1-8
Hi, that is correct, but that strategy alone is not used in any modern implant. If you look at the end of the article you will read about the MPEAK and SPEAK strategies. It's much more common now to use a filterbank with something like 8 to 16 bandpass filters. Of course, how many electrodes you can stimulate depends on the patient.
Wayne King
2012-1-8
You want to bandpass filter of course, but then the zero crossing detector finds the dominant oscillation by noting that there are two zero crossings for every period of a sinusoid. So if you know the number of zero crossings in a given time interval you can estimate the frequency.
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i Venky
2012-1-8
2 个评论
Wayne King
2012-1-8
That's right. You assume there is only one dominant mode of oscillation in that band.
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