Across-site patterns of modulation detection: Relation to speech recognition

Abstract

The aim of this study was to identify across-site patterns of modulation detection thresholds (MDTs) in subjects with cochlear implants and to determine if removal of sites with the poorest MDTs from speech processor programs would result in improved speech recognition. Five hundred millisecond trains of symmetric-biphasic pulses were modulated sinusoidally at 10 Hz and presented at a rate of 900 pps using monopolar stimulation. Subjects were asked to discriminate a modulated pulse train from an unmodulated pulse train for all electrodes in quiet and in the presence of an interleaved unmodulated masker presented on the adjacent site. Across-site patterns of masked MDTs were then used to construct two 10-channel MAPs such that one MAP consisted of sites with the best masked MDTs and the other MAP consisted of sites with the worst masked MDTs. Subjects' speech recognition skills were compared when they used these two different MAPs. Results showed that MDTs were variable across sites and were elevated in the presence of a masker by various amounts across sites. Better speech recognition was observed when the processor MAP consisted of sites with best masked MDTs, suggesting that temporal modulation sensitivity has important contributions to speech recognition with a cochlear implant.

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.…”

“…An alternative approach would be to compare speech recognition using experimental processor maps with stimulation sites for one map selected to have steep slopes and stimulation sites for the other map having shallow slopes. An example of this approach using another psychophysical measure has been published previously (Garadat et al, 2012). In the clinic, stimulation sites with steep integration slopes could be selectively favored in the processor map in an effort to improve speech recognition, similar to the experiment by that selected sites based on modulation detection acuity.…”

“…As was discussed earlier, nerve survival density describes one aspect of neural health and the surviving neurons can vary in many aspects such as myelination, membrane properties, or metabolic function that all potentially affect the functional response to cochlear implant stimulation. It would be interesting to relate the psychophysical measure for nerve survival to measures that assess the temporal processing fidelity of the auditory neurons such as amplitude modulation detection (Garadat et al, 2012;. It remains to be tested whether temporal processing acuity would be dependent on the density of nerve fibers or is a function of other properties of the surviving neurons.…”

Band importance functions of listeners with cochlear implants using clinical maps

“…In cochlear implants, each channel in the device maps an acoustic band to a corresponding electrical stimulation region in the cochlea, so the resultant percept can be influenced by properties of each channel. Many properties vary both across listeners and across each channel in a listener's implant, including loudness growth (Bierer and Nye, 2014;Chatterjee et al, 2000;Fu, 2005), perceptual threshold (Bierer and Nye, 2014;Pfingst et al, 2004), amplitude modulation sensitivity (Chatterjee and Oberzut, 2011;Garadat et al, 2012Garadat et al, , 2013Shannon, 1992;Zhou and Pfingst, 2014), and spread of excitation (Bierer and Faulkner, 2010;Cohen et al, 2003;Hughes and Stille, 2008;Padilla and Landsberger, 2016). These differences suggest that the amount of usable information transmitted by each channel in an implant may vary in a manner that necessitates changes in the listener's reliance on the corresponding frequency bands, thereby altering a listener's BIF.…”

“…Specifically, removing electrodes that have poor amplitude modulation detection thresholds (Garadat et al, 2012(Garadat et al, , 2013 or are indiscriminable from other electrodes (Zwolan et al, 1997) from a map can improve speech intelligibility. Here, we propose the first step in reversing this approach.…”