RP207 - Comparison of Mapping Procedures for Cochlear Implant Recipients with Single-Sided Deafness

Abstract:
Individualizing the map settings may support better outcomes for cochlear implant (CI) users. The method used to assign the maximum comfortable loudness (MCL) levels may influence speech recognition for CI users. This study compared the speech recognition of CI users with unilateral or asymmetric hearing loss with maps that either had MCL levels assigned behaviorally or objectively, using electrically evoked stapedius reflex threshold (eSRT) responses.

Objective:
This report compares the maximum comfortable loudness (MCL) levels assigned using behavioral measures versus an objective measure, specifically the electrically evoked stapedius reflex threshold (eSRT) measure, and assesses speech recognition performance differences between maps using these methods for cochlear implant (CI) users with unilateral and asymmetric hearing loss.

Rationale:
Mapping of a CI device includes defining the electric dynamic range for each active channel by measuring the MCL and threshold (T) levels. MCLs can be measured behaviorally or objectively. The behavioral method involves the patient ranking the perceived loudness of the stimulation from each electrode. The electrically evoked stapedius reflex threshold (eSRT) is an objective measure that can be used to determine the MCL level for each channel by eliciting a response when stimulating each electrode. Some patients have similar MCLs between behavioral and eSRT methods, however, other patients have remarkable differences between these methods. This discrepancy is of particular interest for CI users with normal hearing in the contralateral ear, unilateral hearing loss (UHL), and those with mild to moderate hearing loss in the contralateral ear, asymmetrical hearing loss (AHL). There is limited knowledge on the best way to program CI users with UHL and AHL. It may be important to establish a balance in loudness between the ears to achieve a maximum binaural hearing benefit on spatial hearing tasks. The present study aimed to compare eSRT and behaviorally measured MCL levels among adult CI users with UHL and AHL and assess the differences in binaural hearing between maps.

Design:
Adults with UHL and AHL were seen for routine follow-up and completed a speech recognition in noise task using the AzBio sentences in a 10-talker masker in three spatial separated noise conditions. Participants completed this task in their familiar settings, behaviorally measuring MCL map, first. For the behavioral method, participants ranked the perceived loudness of stimulation and was set to “loud but comfortable.” eSRT values were then collected by placing the tympanometry probe in either the ipsilateral or contralateral ear and using a probe tone of 226Hz, 678Hz, or 1000 Hz and increasing the stimulation level on individual channels until the eSRT was observed. A new map was created with MCL assigned at the eSRT level and speech recognition testing was repeated acutely.

There were individual differences in the relationship between the behavioral and eSRT MCL levels across participants. For some, the behaviorally measured MCL levels approximated the eSRT MCL levels. For others, the behaviorally measured MCL levels were higher (louder) than the eSRT MCL levels. For the latter group, better speech recognition in noise was observed with the eSRT maps than with the behaviorally-measured MCL maps.

Conclusion:
The individualized mapping of MCL levels may include behavioral and/or objective measures to create an optimal map. For some CI users, these methods may produce different levels for MCLs. To improve individualized care and patient outcomes, it is important to understand the optimal ways to program unique patient populations, such as those with UHL and AHL.