Cochlear Implant Signal Processing for Harmonic Resolution
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Solution Overview
Problem
Existing cochlear implant systems fail to effectively integrate tonotopic and periodic pitch cues, leading to complex and unpredictable pitch perceptions due to broad frequency band processing and lack of simultaneous stimulation of both cues, resulting in unwanted changes in pitch perception.
Innovation Solution
The method involves processing acoustic signals into band pass signals, defining macro bands, and decimating stimulation events to select the maximum energy band pass signal within each macro band, while preserving temporal and spectral structures using a pulse selection inhibition function and a weighting matrix that accounts for patient-specific pitch perception characteristics, to generate simultaneous electrode stimulation signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If broad frequency bands are used to cover the acoustic frequency range, then the device complexity is reduced, but the measurement precision of pitch information deteriorates
Solution Approach 1:
The patent divides the frequency spectrum into multiple overlapping macro bands, each containing multiple band pass filters. This segmentation allows the system to use many narrow band pass filters (improving harmonic resolution) while organizing them into a manageable macro band structure (controlling device complexity). The overlapping macro bands ensure smooth transitions and continuous coverage across the frequency range.
2Productivity
If multiple harmonics are processed by each band pass filter, then the productivity of signal processing is improved, but the measurement precision of pitch information deteriorates
Solution Approach 1:
The patent applies local quality by making each band pass filter narrow-band so that it processes only one dominant harmonic at a time. This local specialization ensures high pitch coding accuracy for each filter. The overall system maintains productivity by organizing these specialized filters into overlapping macro bands that collectively cover the entire frequency range, allowing parallel processing of multiple harmonics across different filters.
3Measurement precision
If tonotopic and periodic pitch cues are integrated simultaneously, then the measurement precision of pitch perception is improved, but the device complexity increases
Solution Approach 1:
The patent merges tonotopic and periodic pitch cues by simultaneously extracting both types of information from the same set of band pass filters. Tonotopic pitch is derived from the frequency location of active filters, while periodic pitch is derived from the temporal envelope modulation. Both cues are integrated in the stimulation coding to provide enhanced pitch perception accuracy without requiring separate processing paths, thus controlling device complexity.
4Device complexity
If the number of band pass signals equals the number of stimulation electrodes, then the device complexity is reduced, but the measurement precision of spectral representation deteriorates
Solution Approach 1:
The patent introduces an additional organizational dimension by grouping band pass signals into overlapping macro bands. This allows the system to have more band pass signals than electrodes (improving spectral resolution) while managing complexity through the macro band structure. The macro bands provide a hierarchical organization that simplifies the mapping process from numerous band pass signals to a manageable number of electrodes.
Data Source
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AI summary
Generating electrode stimulation signals for an implanted electrode array is described. An acoustic audio signal is processed to generate band pass signals which represent associated bands of audio frequencies. Macro bands are defined, each of which characterizes multiple band pass signals. The macro bands are processed in a sequence of sampling intervals. For each sampling interval, the processing includes: i. extracting timing and energy information from each band pass signal to form requested stimulation events, ii. decimating the requested stimulation events to select a maximum energy band pass signal within each macro band, and iii. decimating each selected band pass signal based on a pulse selection inhibition function and preserving temporal and spectral structures of the band pass signals so as to generate stimulation event signals. The stimulation event signals are weighted with a weighting matrix reflecting patient-specific pitch perception characteristics to produce output electrode stimulation signals to the implanted electrode array.