Envelope Interactions in Multi-Channel Amplitude Modulation Frequency Discrimination by Cochlear Implant Users.
John J Galvin1, Sandra I Oba2, Deniz Başkent3
1Department of Head and Neck Surgery, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America; Department of Otorhinolaryngology, Head and Neck Surgery, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands; Research School of Behavioral and Cognitive Neurosciences, Graduate School of Medical Sciences, University of Groningen, Groningen, The Netherlands.
Plos One
|October 3, 2015
Summary
Cochlear implant users show improved amplitude modulation frequency discrimination (AMFD) with multiple channels. This study reveals that multiple envelope representations, not just loudness, contribute to this multi-channel advantage in AMFD.
Area of Science:
- Auditory Neuroscience
- Signal Processing in Hearing
- Cochlear Implant Technology
Background:
- Previous studies indicate multi-channel stimulation enhances amplitude modulation frequency discrimination (AMFD) in cochlear implant (CI) users.
- The underlying mechanisms, such as increased loudness or multiple envelope representations, remain unclear.
- Investigating envelope interference can elucidate how multi-channel modulation benefits temporal processing.
Purpose of the Study:
- To measure multi-channel AMFD in CI subjects.
- To investigate the role of envelope interference and channel spacing in AMFD.
- To determine if multiple envelope representations contribute to the multi-channel advantage.
Main Methods:
- A 3-alternative forced-choice procedure was used to measure AMFD in CI subjects.
- Reference AM (100 Hz) was presented to all 3 channels, while target AM varied across channels.
- Electrode spacing was manipulated (wide vs. narrow) to assess channel interaction.
Main Results:
- CI subjects demonstrated high sensitivity to envelope interactions between channels.
- AMFD performance was non-monotonic with target AM frequency.
- A multi-channel advantage was observed, with performance superior to single-channel stimulation.
- Narrow electrode spacing showed greater sensitivity for target AM on a single channel versus all channels at small frequency differences.
Conclusions:
- Multiple envelope representations likely contribute to the multi-channel AMFD advantage, alongside increased loudness.
- Peripheral processing plays a role in multi-channel temporal processing, as suggested by spacing-dependent results.
- Non-monotonic performance indicates adaptive procedures may be unsuitable for AMFD with interfering envelopes.
- Envelope interactions in multi-channel systems are complex and depend on channel independence and presented information.
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