Cochlear Implant Harmonic Tracking for Precise Stimulation Timing
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Solution Overview
Problem
Current cochlear implant systems face challenges in accurately estimating instantaneous frequencies, especially in the presence of multiple harmonics and noise, leading to poor speech intelligibility and pitch perception due to the broad frequency bands and limited filter bank resolution.
Innovation Solution
The implementation of an active contour model to estimate dominant frequencies from a spectrogram generated by short-time Fourier transformation, allowing for channel-specific sampling sequences and improved stimulation timing signals for electrode contacts in the cochlear implant array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional filter bank methods are used for frequency estimation in cochlear implants, then the system complexity remains low, but the measurement precision of instantaneous frequencies deteriorates due to broad frequency bands and limited resolution
Solution Approach 1:
The patent segments the spectrogram into multiple horizontal strips representing different time frames, and applies active contour models to each strip independently to detect harmonic frequencies. This segmentation approach enables precise frequency estimation across different time periods while managing computational complexity through localized processing.
Solution Approach 2:
The patent transforms the frequency estimation problem from traditional time-domain or simple frequency-domain analysis to a two-dimensional spectrogram domain, where active contour models can track harmonic trajectories across both time and frequency dimensions simultaneously, improving measurement precision.
2Measurement precision
If broad frequency bands are used in cochlear implant electrode channels, then the device complexity is reduced, but the measurement precision of instantaneous frequencies worsens due to inability to resolve individual harmonics
Solution Approach 1:
By moving to the spectrogram domain (adding the time dimension to frequency analysis), the patent can resolve individual harmonics even within broad frequency bands by tracking their temporal evolution, achieving high frequency resolution without requiring complex filter banks.
Solution Approach 2:
The patent performs preliminary spectrogram computation and harmonic tracking before electrode stimulation, extracting precise instantaneous frequency information in advance. This preliminary frequency estimation allows the use of simpler electrode channel designs while maintaining high measurement precision.
3Loss of information
If simple envelope-based stimulation is used, then the device complexity remains low, but the loss of information increases due to inability to preserve fine structure and pitch information
Solution Approach 1:
The patent uses the time-frequency representation of the spectrogram to preserve fine structure information that is lost in traditional envelope-only processing. By tracking harmonic trajectories in the spectrogram domain, the system maintains pitch and fine structure information while using envelope-based stimulation.
Solution Approach 2:
The active contour model acts as an intermediary that extracts precise instantaneous frequency and fine structure information from the spectrogram, which then guides the envelope-based stimulation timing. This intermediary processing preserves critical information without requiring complex direct stimulation schemes.
Data Source
AI summary
A signal processing arrangement generates electrical stimulation signals to electrode contacts in an implanted cochlear implant array. An input sound signal is processed to generate band pass signals that each represent an associated band of audio frequencies. A spectrogram representative of frequency spectrum present in the input sound signal is generated. A characteristic envelope signal is produced for each band pass signal based on its amplitude. An active contour model is applied to estimate dominant frequencies present in the spectrogram, and the estimate is used to generate stimulation timing signals for the input sound signal. The electrode stimulation signals are produced for each electrode contact based on the envelope signals and the stimulation timing signals.