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Frequency transposition around dead regions simulated with a noiseband vocoder
Deniz Başkent1, Robert V Shannon
1Department of Biomedical Engineering, University of Southern California, Los Angeles, California 90089, USA. deniz_baskent@starkey.com
The Journal of the Acoustical Society of America
|March 9, 2006
Summary
Simulating cochlear dead regions in hearing loss, this study found that while frequency transposition offers more acoustic information, speech perception did not significantly improve, likely due to spectral distortions.
Area of Science:
- Auditory Neuroscience
- Speech Perception
- Cochlear Implant Technology
Background:
- Sensorineural hearing loss can cause cochlear 'dead regions' disrupting auditory information transmission.
- Cochlear implants may face similar challenges if spiral ganglia are non-functional, creating artificial dead regions.
- Previous research simulated dead regions using noiseband vocoders and tested phoneme recognition under different mapping conditions.
Purpose of the Study:
- To extend previous findings by investigating a frequency transposition mapping condition for simulated cochlear dead regions.
- To evaluate the impact of different frequency-place mappings on speech perception in the presence of simulated dead regions.
- To compare the effectiveness of frequency transposition versus removal or reassignment of acoustic information in dead regions.
Main Methods:
- Simulated cochlear dead regions of varying sizes and locations using a noiseband vocoder.
- Tested normal-hearing subjects on phoneme recognition under three frequency-place mapping conditions: removal, reassignment, and frequency transposition.
- Compared acoustic information provided by frequency transposed maps versus maps with removed frequency ranges.
Main Results:
- The frequency transposed map provided more acoustic information compared to the map where the dead region's frequency range was removed.
- Despite increased acoustic information, speech perception did not improve for many simulated dead region conditions.
- Spectral distortions introduced by the frequency-place mapping likely limited speech perception benefits.
Conclusions:
- Frequency transposition mapping in simulated cochlear dead regions offers greater acoustic information but does not consistently enhance speech perception.
- Spectral distortions inherent in frequency-place mapping strategies are a significant factor affecting speech intelligibility.
- Further research is needed to optimize frequency-place mapping strategies for cochlear implant users with cochlear dead regions.
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