Document Detail

Variations in carrier pulse rate and the perception of amplitude modulation in cochlear implant users.
MedLine Citation:
PMID:  22367093     Owner:  NLM     Status:  MEDLINE    
OBJECTIVES: A major focus of recent attempts to enhance cochlear implant (CI) systems has been to increase the rate at which pulses are delivered to the electrode array. One basis for these attempts has been the expectation that faster stimulation rates would lead to an enhanced representation of temporal modulation information. However, there is recent physiological and behavioral evidence to suggest that the reverse may be the case. Here, the effects of stimulation rate on the perception of amplitude modulation were assessed using both modulation detection and modulation frequency discrimination tasks for a range of pulse rates extending considerably higher than the highest rate tested in previous studies and for different speech-relevant modulation frequencies.
DESIGN: Detection of sinusoidal amplitude modulation was assessed in five CI users using monopolar pulse trains presented to a single electrode at rates of 482, 723, 1447, 2894, and 5787 pulses per second (pps). Adaptive procedures were used to find the minimal detectable modulation depth at modulation frequencies of 10 and 100 Hz and at carrier levels of 25%, 50%, and 75% of the electrode's dynamic range. Discrimination of modulation frequency was examined for the same range of pulse rates for the highest carrier level. Similar adaptive procedures determined the minimum increase in modulation frequency that could be detected relative to reference modulation frequencies of 10, 100, and 200 Hz. In both tasks, level roving was implemented to minimize possible loudness cues.
RESULTS: Consistent with previous evidence, modulation detection thresholds were better for higher carrier levels and lower modulation frequencies. When modulation depth at threshold was expressed in terms of the ratio of the depth of the modulation and the carrier level in dB (i.e., 20 log m), performance was significantly better at lower pulse rates. However, when modulation depth was expressed relative to dynamic range, the effect of pulse rate was no longer significant, reflecting the fact that dynamic range increases with pulse rate. Modulation frequency discrimination clearly worsened with increasing modulation frequency, but there was no significant effect of pulse rate.
CONCLUSIONS: In contrast to some recent evidence, no clearly harmful effect of higher pulse rates on modulation perception was found. However, even with very fast stimulation rates, tested over a wide range of modulation frequencies and with two different tasks, there is no evidence of benefit from faster stimulation rates in the perception of amplitude modulation.
Tim Green; Andrew Faulkner; Stuart Rosen
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Publication Detail:
Type:  Clinical Trial; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Ear and hearing     Volume:  33     ISSN:  1538-4667     ISO Abbreviation:  Ear Hear     Publication Date:    2012 Mar-Apr
Date Detail:
Created Date:  2012-02-27     Completed Date:  2012-06-26     Revised Date:  2012-08-24    
Medline Journal Info:
Nlm Unique ID:  8005585     Medline TA:  Ear Hear     Country:  United States    
Other Details:
Languages:  eng     Pagination:  221-30     Citation Subset:  IM    
University College London, Speech Hearing and Phonetic Sciences, London, United Kingdom.
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MeSH Terms
Auditory Perception / physiology*
Auditory Threshold / physiology
Cochlear Implantation / instrumentation,  methods*
Cochlear Implants*
Cochlear Nerve / physiology
Deafness / physiopathology*,  rehabilitation*
Discrimination (Psychology) / physiology
Electric Stimulation / methods
Loudness Perception / physiology
Middle Aged
Grant Support
G19//Action on Hearing Loss

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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