Abstract
Temporal cues are important for cochlear implant (CI) users when listening to speech. Users with greater sensitivity to temporal modulations show better speech recognition and modifications to stimulation parameters based on modulation sensitivity have resulted in improved speech understanding. Behavioural measures of temporal sensitivity require cooperative participants and a large amount of time. These limitations have motivated the desire for an objective measure with which to appraise temporal sensitivity for CI users.Electrically evoked auditory steady state responses (EASSRs) are neural responses to periodic electrical stimulation that have been used to predict threshold (T) levels. In this study we evaluate the use of EASSRs as a tool for assessing temporal modulation sensitivity.Modulation sensitivity was assessed behaviourally using modulation detection thresholds (MDTs) for a 20 Hz rate. On the same stimulation sites, EASSRS were measured using sinusoidally amplitude modulated pulse trains at 4 and 40 Hz. Measurements were taken using a bipolar configuration on 12 electrode pairs over 5 participants. Results showed that EASSR amplitudes and signal-to-noise ratios (SNRs) were significantly related to the MDTs. Larger EASSRs corresponded with sites of improved modulation sensitivity. This relation was driven by across-subject variation. This result indicates that EASSRs may be used as an objective measure of site-specific temporal sensitivity for CI users.
Highlights
Cochlear implant (CI) recipients often understand speech well in quiet conditions but in difficult listening environments their performance worsens and becomes variable
Both objective evoked auditory steady state responses (EASSRs) and behavioural modulation detection thresholds (MDTs) were measured for 12 cochlear implant electrode pairs in five participants
Regression analysis showed that the 40-Hz EASSR was significantly related with the MDT, confirming the hypothesis that EASSRs may be used to assess site-specific temporal sensitivity
Summary
Cochlear implant (CI) recipients often understand speech well in quiet conditions but in difficult listening environments their performance worsens and becomes variable. A proposed cause for some of the remaining variability in performance is perceptual variance along the tonotopic axis caused by the quality of each electrode neuron interface (ENI) (Pfingst et al, 2008; Bierer and Faulkner, 2010). Reducing these perceptual variations, by adjusting the stimulation parameters of individual sites, has been suggested as a means for improving speech performance (Zwolan et al, 1997; Pfingst et al, 2008).
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