Cochlear Implant Channel-Specific Loudness Mapping
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Solution Overview
Problem
Existing cochlear implant systems do not accurately account for psychoacoustic properties of normal hearing, such as equal-loudness contours, leading to reduced dynamic range and suboptimal loudness perception in users, as they rely on pre-emphasis filters that attenuate low frequencies and fail to consider sound level dependencies.
Innovation Solution
Implementing channel-specific loudness mapping using independent logarithmic functions and frequency-dependent threshold levels based on ISO normal hearing contours, allowing for optimal loudness growth and balanced stimulation across electrodes, thereby maximizing the usable dynamic range and mimicking natural loudness perception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a pre-emphasis filter is used to reflect ISO loudness contours, then loudness perception is improved, but dynamic range is reduced due to signal attenuation
Solution Approach 1:
The patent applies parameter changes by using channel-specific loudness mapping functions with different mapping parameters (c1, c2, c3, c4) for different frequency bands instead of a single fixed mapping parameter. This allows the system to adjust the compression characteristics dynamically across different channels to maintain both loudness perception and dynamic range.
Solution Approach 2:
The patent segments the frequency spectrum into multiple bands (low, mid-low, mid-high, high frequencies) and applies different loudness mapping functions to each band. This segmentation allows independent optimization of loudness perception for each frequency range while preserving overall dynamic range through channel-specific processing.
2Device complexity
If a single identical loudness mapping function is applied to all channels, then device complexity is reduced, but manufacturing precision of loudness perception is worsened
Solution Approach 1:
The patent applies local quality by making each frequency band channel have its own specific loudness mapping function with unique parameters (c1, c2, c3, c4 for each band). This allows each channel to be optimized for its specific frequency characteristics and loudness perception requirements, improving overall mapping accuracy while maintaining manageable complexity through modular implementation.
3Illumination intensity
If pre-emphasis filter attenuates low frequency signals, then loudness contour matching is improved, but signal accuracy is reduced
Solution Approach 1:
The patent replaces the traditional pre-emphasis filter approach with a digital signal processing system that uses channel-specific loudness mapping functions. Instead of mechanically attenuating low frequencies before processing, the system digitally adjusts the mapping parameters for each frequency band to achieve both loudness contour matching and signal accuracy preservation.
Data Source
AI summary
A method is described for generating electrode stimulation signals for an implanted electrode array. An acoustic audio signal is processed to generate band pass signals each representing an associated band of audio frequencies. Stimulation information is extracted from the band pass signals to generate stimulation event signals defining electrode stimulation signals. The stimulation event signals are mapped according to independent channel-specific loudness functions to produce a set of electrode stimulation signals within channel-specific minimum and maximum threshold levels. The electrode stimulation signals are developed into a set of output electrode pulses to the electrodes in the implanted electrode array.