Cochlear Implant Monophasic Pulse Polarity for Charge Balance
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Solution Overview
Problem
Existing cochlear implant speech coding strategies fail to effectively transmit both signal envelopes and fine time structures, particularly in noisy and reverberant conditions, limiting speech understanding and localization.
Innovation Solution
A novel monophasic stimulation pulse strategy with alternating polarity is employed, where each electrode contact receives a sequence of monophasic pulses with polarity changes based on accumulated charge imbalance, ensuring charge balance over time, and incorporating interpulse intervals for neural response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional biphasic stimulation pulses are used to ensure charge balance, then safety is maintained, but speech understanding and localization in noisy conditions deteriorate due to inability to transmit fine time structure
Solution Approach 1:
The stimulation pulse is segmented into multiple phases: a first monophasic pulse with first polarity, followed by a second monophasic pulse with opposite polarity. This segmentation allows the system to transmit fine time structure information through the timing and polarity variations while maintaining charge balance across the two phases, thus resolving the contradiction between safety and information transmission.
Solution Approach 2:
The patent employs periodic alternation of pulse polarities in a systematic pattern. By periodically switching between positive and negative polarity pulses according to specific rules based on charge imbalance, the system maintains long-term charge balance while encoding fine time structure information in the temporal pattern of polarity changes, thereby improving speech understanding in noise without compromising safety.
2Loss of information
If monophasic pulses with alternating polarity are used to transmit fine time structure, then speech understanding in noise improves, but charge imbalance accumulates causing safety concerns
Solution Approach 1:
The system incorporates a feedback mechanism that monitors the accumulated charge imbalance after each pulse and uses this information to determine the polarity of subsequent pulses. When charge imbalance exceeds a threshold, the system adjusts the polarity sequence to restore balance, ensuring safety is maintained while preserving fine time structure transmission capabilities.
Solution Approach 2:
The patent dynamically changes the polarity parameter of stimulation pulses based on real-time charge imbalance conditions. By adjusting the polarity sequence according to accumulated charge, the system maintains charge balance safety while allowing monophasic pulses to effectively transmit fine time structure information during periods when charge balance permits.
3Reliability
If longer interpulse intervals are used to allow neural response, then neural stimulation effectiveness improves, but transmission rate of speech information deteriorates
Solution Approach 1:
The patent implements dynamic adjustment of interpulse intervals based on the specific neural response requirements of different electrode contacts and stimulation conditions. By optimizing the timing between pulses dynamically, the system ensures sufficient neural response time while maximizing the information transmission rate, thus resolving the contradiction between reliability and productivity.
Data Source
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AI summary
Arrangements are described for generating electrode stimulation signals to electrode contacts in an implanted cochlear implant electrode array. Electrode stimulation signals are a sequence of monophasic stimulation pulses varying in polarity between positive polarity and negative polarity with successive pulses separated in time by an interpulse interval sufficient for neural response. Accumulated charge imbalance and charge imbalance polarity are calculated for each electrode contact after each stimulation pulse. For each electrode contact a stimulation pulse has the same polarity as an immediately preceding stimulation pulse for that electrode contact only when the charge imbalance polarity has opposite polarity from the immediately preceding stimulation pulse for that electrode contact, and the accumulated charge imbalance exceeds a defined charge imbalance threshold value. Otherwise, each stimulation pulse has the opposite polarity as the immediately preceding stimulation pulse for that electrode contact.