Journal
JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA
Volume 121, Issue 4, Pages 2236-2246Publisher
ACOUSTICAL SOC AMER AMER INST PHYSICS
DOI: 10.1121/1.2537501
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Funding
- NIDCD NIH HHS [P30 DC005188, R01 DC003808, R01 DC04312, P30 DC005188-05, R01 DC004312-07, P30 DC05188, R01 DC003808-05, R01 DC004312, R01 DC03808] Funding Source: Medline
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Most modern cochlear-implant speech processors convey speech-envelope information using amplitude-modulated pulse trains. The use of higher-rate carrier pulse trains allows more envelope detail in the signal. However, neural response properties could limit the efficacy of high-rate carriers. This study, examined effects of carrier rate and stimulation site, on psychophysical modulation detection thresholds (MDTs). Both of these variables could affect the neural representation of the carrier and thus affect perception of the modulation. Twelve human subjects with cochlear implants were tested. Phase duration of symmetric biphasic pulses was modulated sinusoidally at 40 Hz. MDTs were determined for monopolar stimulation at two carrier rates [250 and 4000 pulses/s (pps)], three stimulation sites (basal, middle, and apical), and five stimulus levels (10%, 30%, 50%, 70%, and 90% of the dynamic range). MDTs were lower for 250 pps carriers than for 4000 pps carriers in 71% of the 180 cases studied. Effects of carrier rate were greatest at the apical stimulation site and effects of stimulation site on MDTs depended on carrier rate. The data suggest a distinct disadvantage to using carrier pulse rates as high as 4000 pps. Stimulation site should be considered in evaluating modulation detection ability. (c) 2007 Acoustical Society of America.
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