Relationships Among Peripheral and Central Electrophysiological Measures of Spatial and Spectral Selectivity and Speech Perception in Cochlear Implant Users

Abstract

Objectives The ability to perceive speech is related to the listener’s ability to differentiate among frequencies (i.e., spectral resolution). Cochlear implant (CI) users exhibit variable speech-perception and spectral-resolution abilities, which can be attributed in part to the extent of electrode interactions at the periphery (i.e., spatial selectivity). However, electrophysiological measures of peripheral spatial selectivity have not been found to correlate with speech perception. The purpose of this study was to evaluate auditory processing at the periphery and cortex using both simple and spectrally complex stimuli to better understand the stages of neural processing underlying speech perception. The hypotheses were that (1) by more completely characterizing peripheral excitation patterns than in previous studies, significant correlations with measures of spectral selectivity and speech perception would be observed, (2) adding information about processing at a level central to the auditory nerve would account for additional variability in speech perception, and (3) responses elicited with spectrally complex stimuli would be more strongly correlated with speech perception than responses elicited with spectrally simple stimuli. Design Eleven adult CI users participated. Three experimental processor programs (MAPs) were created to vary the likelihood of electrode interactions within each participant. For each MAP, a subset of 7 of 22 intracochlear electrodes was activated: adjacent (MAP 1), every-other (MAP 2), or every third (MAP 3). Peripheral spatial selectivity was assessed using the electrically evoked compound action potential (ECAP) to obtain channel-interaction functions for all activated electrodes (13 functions total). Central processing was assessed by eliciting the auditory change complex (ACC) with both spatial (electrode pairs) and spectral (rippled noise) stimulus changes. Speech-perception measures included vowel-discrimination and the Bamford-Kowal-Bench Sentence-in-Noise (BKB-SIN) test. Spatial and spectral selectivity and speech perception were expected to be poorest with MAP 1 (closest electrode spacing) and best with MAP 3 (widest electrode spacing). Relationships among the electrophysiological and speech-perception measures were evaluated using mixed-model and simple linear regression analyses. Results All electrophysiological measures were significantly correlated with each other and with speech perception for the mixed-model analysis, which takes into account multiple measures per person (i.e. experimental MAPs). The ECAP measures were the best predictor of speech perception. In the simple linear regression analysis on MAP 3 data, only the cortical measures were significantly correlated with speech; spectral ACC amplitude was the strongest predictor. Conclusions The results suggest that both peripheral and central electrophysiological measures of spatial and spectral selectivity provide valuable information about speech perception. Clinically, it is often desirable to optimize pe...

Peripheral and Central Contributions to Cortical Responses in Cochlear Implant Users

“…Two extracochlear electrodes (MP1, positioned under the temporalis muscle; MP2, located on the case of the receiver-stimulator) are available for monopolar stimulation modes (Patrick et al 2006). The measurements for this and the companion study (Scheperle & Abbas, submitted) were obtained using a laboratory Freedom processor and headpiece.…”

“…The data collected for this and the companion study (Scheperle & Abbas, submitted) required a total of 12–20 hours of participation for most individuals. Each session ranged from 4–8 hours, and the time between the first and last sessions ranged from approximately 1 week to 7 months.…”

“…Spatial selectivity was evaluated because the goal was to extend this work to predictions of speech perception (Scheperle & Abbas, submitted). ECAP channel-interaction functions were obtained on more than half of the electrode array, which allowed a more thorough characterization of peripheral spatial selectivity for each participant than the relatively sparse sampling of previous studies (Cohen et al 2003; Hughes & Stille 2008; Tang et al 2011; van der Beek et al 2012).…”

Assessing the Electrode-Neuron Interface with the Electrically Evoked Compound Action Potential, Electrode Position, and Behavioral Thresholds

“…ECAPs were obtained using a forward-masking, channel-interaction paradigm (Cohen et al 2003;Abbas et al 2004;Scheperle and Abbas 2015). Stimuli were biphasic, cathodic-leading pulses (32 μs/phase, 0 μs interphase gap) presented at a probe rate of 20 per second in the MP configuration.…”

“…Like ECAP amplitudes, the shapes of the resulting channel interaction functions (CIFs) are quite variable from channel-to-channel (e.g., Scheperle and Abbas, 2015). CIFs have been shown to strongly correlate with psychophysical tuning curves and forward masking pattern widths (Cohen et al 2003;Abbas et al 2004;Stille 2008, 2010), suggesting that those two metrics reflect similar underlying processes.…”