The effect of interaural fluctuation rate on correlation change discrimination
Matthew J Goupell1, Ruth Y Litovsky
1Department of Hearing and Speech Sciences, University of Maryland, College Park, MD, 20742, USA, goupell@umd.edu.
Journal of the Association for Research in Otolaryngology : JARO
|November 22, 2013
Summary
Bilateral cochlear implants (CIs) may offer limited binaural benefits due to increased interaural fluctuation rates. This study found that while fast rates are not detrimental, other CI-related deficiencies might limit these benefits in users.
Area of Science:
- Auditory Neuroscience
- Signal Processing
- Hearing Science
Background:
- Bilateral cochlear implants (CIs) offer some binaural benefits, but these are less pronounced than in normal-hearing (NH) listeners.
- The wider frequency-to-electrode mapping in CIs, compared to normal auditory filters, increases interaural fluctuation rates, potentially limiting binaural unmasking.
- Understanding the role of interaural fluctuation rate is crucial for improving binaural hearing in CI users.
Purpose of the Study:
- To investigate the impact of interaural fluctuation rate on correlation change discrimination and binaural masking-level differences.
- To simulate CI processing in normal-hearing listeners using a pulsed-sine vocoder to isolate the effects of interaural fluctuation rate.
- To identify factors contributing to the reduced binaural benefits observed in cochlear implant users.
Main Methods:
- Experiment 1: Measured correlation-change just-noticeable differences (JNDs) and tone-in-noise thresholds with varying bandwidths (BWs) and center frequencies (CFs).
- Experiment 2: Systematically varied interaural fluctuation rate using a pulsed-sine vocoder, dissociating it from BW and CF.
- Experiment 3: Manipulated BW, CF, and vocoder pulse rate while keeping interaural fluctuation rate constant.
Main Results:
- Correlation change discrimination was influenced by BW, CF, and interaural fluctuation rate.
- Interaural fluctuation rate did not affect correlation change JNDs for correlated noises but increased them for uncorrelated noises at slow rates.
- Increasing BW increased JNDs, while increasing CF decreased JNDs.
Conclusions:
- Fast interaural fluctuation rates do not appear to hinder the detection of interaural correlation changes.
- The limited binaural benefits in cochlear implant users may stem from other temporal or spectral processing deficiencies inherent to electrical stimulation.
- Further research into CI signal processing is needed to enhance binaural hearing.
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