Across-site patterns of modulation detection in listeners with cochlear implants

Abstract

In modern cochlear implants, much of the information required for recognition of important sounds is conveyed by temporal modulation of the charge per phase in interleaved trains of electrical pulses. In this study, modulation detection thresholds (MDTs) were used to assess listeners' abilities to detect sinusoidal modulation of charge per phase at each available stimulation site in their 22-electrode implants. Fourteen subjects were tested. MDTs were found to be highly variable across stimulation sites in most listeners. The across-site patterns of MDTs differed considerably from subject to subject. The subject-specific patterns of across-site variability of MDTs suggest that peripheral site-specific characteristics, such as electrode placement and the number and condition of surviving neurons, play a primary role in determining modulation sensitivity. Across-site patterns of detection thresholds (T levels), maximum comfortable loudness levels (C levels) and dynamic ranges (DRs) were not consistently correlated with across-site patterns of MDTs within subjects, indicating that the mechanisms underlying across-site variation in these measures differed from those underlying across-site variation in MDTs. MDTs sampled from multiple sites in a listener's electrode array might be useful for diagnosing across-subject differences in speech recognition with cochlear implants and for guiding strategies to improve the individual's perception.

Relationship between multipulse integration and speech recognition with cochlear implants

“…This suggests an uneven distribution of pathology along the tonotopic axis. Across-site variation has been found for various psychophysical measures (Zwolan et al, 1997;Pfingst et al, 2004;Pfingst and Xu, 2005;Bierer, 2007;Bierer and Faulkner, 2010;Pfingst et al, 2008;Garadat et al, 2012), and the patterns in which these psychophysical measures vary across the stimulation sites are also unique to each measure (Pfingst et al, 2011a). The unique patterns suggest that the various psychophysical measures are not mediated by a single mechanism.…”

Detection of pulse trains in the electrically stimulated cochlea: Effects of cochlear health

“…In addition, psychophysical measures of detection and discrimination of electrical stimuli show considerable variation across stimulation sites within individual implants (Donaldson et al, 1997;Pfingst and Xu, 2004;Bierer, 2007;Pfingst et al, 2008). It is commonly assumed that this variation in perception is due in part to variation in cochlear pathology across subjects and along the length of the implanted cochlea within subjects.…”

Effects of stimulus duration on amplitude modulation processing with cochlear implants

“…CI speech performance has been significantly correlated with thresholds for AM detection and AM frequency discrimination, suggesting the importance of temporal AM processing for CI users (Fu, 2002;Chatterjee and Peng, 2008;Luo et al, 2008). Various stimulation parameters have been shown to affect CI users' AM detection thresholds (AMDTs), such as AM frequency (Shannon, 1992), stimulation level (Fu, 2002), electrode location (Pfingst et al, 2008), and stimulation rate Fu, 2005, 2009;Pfingst et al, 2007). However, AM frequency discrimination thresholds (AMFDTs) may be a more relevant measure of CI users' temporal pitch sensitivity, as it may better reflect sensitivity to pitch changes in dynamic stimuli such as speech (e.g., intonation, lexical tones, etc.).…”