Cochlear Implant Signal Processing for Melody Perception
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Solution Overview
Problem
Cochlear implants are limited in their ability to extract and deliver useful information from high-frequency portions of acoustic inputs, leading to poor performance in noisy environments and music perception due to the loss of temporal fine structure cues.
Innovation Solution
The implementation of a coherent demodulation technique that shifts sub-band signals to their base band, generating a low-frequency, real coherent envelope signal that encodes both temporal envelope and fine structure cues, compatible with existing cochlear implant technology, using single sideband demodulation and coherent envelope separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If conventional envelope extraction techniques (Hilbert transform, FFT magnitude) are used in cochlear implants, then the implant can deliver slowly varying envelope cues, but useful information from high-frequency portions of acoustic inputs is lost
Solution Approach 1:
The patent segments the acoustic signal into multiple frequency sub-bands using bandpass filters. Each sub-band is then processed independently to extract both envelope and temporal fine structure information. This segmentation allows the system to handle high-frequency information separately without overwhelming the overall processing complexity.
Solution Approach 2:
The patent changes the processing parameters by extracting temporal fine structure cues (phase information) in addition to envelope cues from each sub-band. The temporal fine structure is derived by analyzing the zero-crossing rates and phase variations of the bandpass-filtered signals, transforming how high-frequency information is utilized in cochlear implants.
2Reliability
If only envelope cues are delivered to cochlear implant electrodes, then the implant operation is simplified, but speech recognition in noisy environments and music perception deteriorate
Solution Approach 1:
The patent merges envelope cues and temporal fine structure cues into a unified stimulation strategy. Both types of information are extracted from the same bandpass-filtered sub-bands and combined to control the cochlear implant electrodes, providing complementary information that improves speech recognition in noise and music perception while maintaining operational feasibility.
Solution Approach 2:
The patent introduces temporal fine structure analysis as an intermediary processing step between bandpass filtering and electrode stimulation. This intermediary extraction of phase and zero-crossing information mediates between the raw acoustic signal and the final stimulation pattern, adding valuable high-frequency information without directly complicating the electrode drive circuitry.
3Measurement precision
If high-frequency temporal fine structure cues are extracted and delivered, then speech and music perception improves, but the processing complexity and computational requirements increase
Solution Approach 1:
The patent performs preliminary bandpass filtering of the acoustic signal into multiple frequency sub-bands before extracting temporal fine structure cues. This preliminary segmentation simplifies subsequent processing by confining high-frequency analysis to specific frequency ranges, reducing the overall computational burden while maintaining extraction accuracy.
Solution Approach 2:
The patent applies partial processing to different frequency regions by focusing temporal fine structure extraction primarily on high-frequency sub-bands where envelope cues are insufficient. Not all sub-bands require equally complex processing, allowing the system to achieve improved perception with moderate overall complexity by applying enhanced processing only where most beneficial.
Data Source
AI summary
The restoration of melody perception is a key remaining challenge in cochlear implants. A novel sound coding strategy is proposed that converts an input audio signal into time-varying electrically stimulating pulse trains. A sound is first split into several frequency sub-bands with a fixed filter bank or a dynamic filter bank tracking harmonics in sounds. Each sub-band signal is coherently downward shifted to a low-frequency base band. These resulting coherent envelope signals have Hermitian symmetric frequency spectrums and are thus real-valued. A peak detector or high-rate sampler of half-wave rectified coherent envelope signals in each sub-band further converts the coherent envelopes into rate-varying, interleaved pulse trains. Acoustic simulations of cochlear implants using this new technique with normal hearing listeners, showed significant improvement in melody recognition over the most common conventional stimulation approach used in cochlear implants.