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Simulations of cochlear implant hearing using filtered harmonic complexes: implications for concurrent sound
John M Deeks1, Robert P Carlyon
1MRC Cognition and Brain Sciences Unit, 15 Chaucer Road, Cambridge CB2 2EF, United Kingdom.
The Journal of the Acoustical Society of America
|April 23, 2004
Summary
Simulations of cochlear implant hearing explored temporal codes for speech segregation. Results suggest that varying pulse rates between target and masker sounds is unlikely to aid in separating concurrent speech signals.
Area of Science:
- Auditory Neuroscience
- Speech Perception
- Cochlear Implant Technology
Background:
- Speech segregation, the ability to separate concurrent sounds, is a challenge for cochlear implant (CI) users.
- Temporal codes, particularly the rate of neural firing, are crucial for auditory processing in CI simulations.
Purpose of the Study:
- To investigate the efficacy of temporal codes, specifically pulse rate, in improving speech segregation within CI simulations.
- To determine if manipulating pulse rates between target and masker signals enhances speech understanding.
Main Methods:
- Two experiments utilized simulations of CI hearing, filtering sentences into six bands.
- Modulation of filtered harmonic complexes was performed using sentence envelopes at pulse rates of 80 or 140 pulses per second (pps).
- Experiment 2 involved presenting target sentences against time-reversed masker sentences with a -9 dB scaling and temporal offset.
Main Results:
- Single-sentence identification improved at the higher pulse rate (140 pps) in Experiment 1.
- In Experiment 2, improved masker-target separation occurred only when the masker's pulse rate differed from the target's (140 pps).
- Channel separation (odd/even) worsened overall performance but showed similar pulse rate effects.
Conclusions:
- Differences in pulse rate between concurrent sounds are unlikely to be a significant factor for improving speech segregation in cochlear implant users.
- Findings suggest limitations in leveraging temporal pulse rate differences for enhanced auditory scene analysis in simulated CI listening conditions.