Across- and within-channel envelope interactions in cochlear implant listeners

Monita Chatterjee, Sandra I. Oba

Research output: Contribution to journalArticle

14 Scopus citations

Abstract

The effects of modulated maskers on detection thresholds of a 50-Hz sinusoidal amplitude modulation (SAM) in a signal carrier were measured in nine cochlear implant (CI) listeners as a function of masker envelope type and for different masker-signal electrode separations. Both signal and masker were 200-ms-long pulse trains, presented concurrently in an interleaved stimulation mode. Masker envelopes were SAM at 20, 50, (0- and π-phase re: the signal modulator), and 125 Hz, as well as noise amplitude modulated (NAM), all with a fixed 20% modulation depth. Comparisons were made against steady-state maskers that had an amplitude equal to the mean amplitude of the modulated maskers or to their peak amplitude (SSpeak). Modulation thresholds were larger in the presence of the dynamic maskers versus the SSpeak maskers; however, there was significant intersubject variability in the pattern of results. Effects of relative phase between masker and signal were not consistent across subjects. Envelope masking (the dB difference in modulation detection thresholds between modulated and SSpeak maskers) was generally larger for the lower-modulation-frequency maskers than the 125-Hz masker. The spatial distribution of masked modulation detection thresholds was found to be considerably different from spatial forward-masking patterns obtained in the same subjects. Finally, modulation thresholds measured for a very wide separation between the masker and signal showed significant envelope masking. These results suggest that, as has been shown in acoustic stimulation, central, across-channel temporal processing mechanisms also occur in electrical stimulation.

Original languageEnglish (US)
Pages (from-to)360-375
Number of pages16
JournalJARO - Journal of the Association for Research in Otolaryngology
Volume5
Issue number4
DOIs
StatePublished - Dec 2004

Keywords

  • Channel interaction
  • Cochlear implants
  • Envelope processing
  • Modulation detection interference

ASJC Scopus subject areas

  • Otorhinolaryngology
  • Sensory Systems

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