Background: The use of bilateral amplification is now common clinical practice for hearing aid
users but not for cochlear implant recipients. In the past, most cochlear implant
recipients were implanted in one ear and wore only a monaural cochlear implant processor.
There has been recent interest in benefits arising from bilateral stimulation that
may be present for cochlear implant recipients. One option for bilateral stimulation
is the use of a cochlear implant in one ear and a hearing aid in the opposite nonimplanted
ear (bimodal hearing).
Purpose: This study evaluated the effect of wearing a cochlear implant in one ear and a digital
hearing aid in the opposite ear on speech recognition and localization.
Research Design: A repeated-measures correlational study was completed.
Study Sample: Nineteen adult Cochlear Nucleus 24 implant recipients participated in the study.
Intervention: The participants were fit with a Widex Senso Vita 38 hearing aid to achieve maximum
audibility and comfort within their dynamic range.
Data Collection and Analysis: Soundfield thresholds, loudness growth, speech recognition, localization, and subjective
questionnaires were obtained six–eight weeks after the hearing aid fitting. Testing
was completed in three conditions: hearing aid only, cochlear implant only, and cochlear
implant and hearing aid (bimodal). All tests were repeated four weeks after the first
test session. Repeated-measures analysis of variance was used to analyze the data.
Significant effects were further examined using pairwise comparison of means or in
the case of continuous moderators, regression analyses. The speech-recognition and
localization tasks were unique, in that a speech stimulus presented from a variety
of roaming azimuths (140 degree loudspeaker array) was used.
Results: Performance in the bimodal condition was significantly better for speech recognition
and localization compared to the cochlear implant–only and hearing aid–only conditions.
Performance was also different between these conditions when the location (i.e., side
of the loudspeaker array that presented the word) was analyzed. In the bimodal condition,
the speech-recognition and localization tasks were equal regardless of which side
of the loudspeaker array presented the word, while performance was significantly poorer
for the monaural conditions (hearing aid only and cochlear implant only) when the
words were presented on the side with no stimulation. Binaural loudness summation
of 1–3 dB was seen in soundfield thresholds and loudness growth in the bimodal condition.
Measures of the audibility of sound with the hearing aid, including unaided thresholds,
soundfield thresholds, and the Speech Intelligibility Index, were significant moderators
of speech recognition and localization. Based on the questionnaire responses, participants
showed a strong preference for bimodal stimulation.
Conclusions: These findings suggest that a well-fit digital hearing aid worn in conjunction with
a cochlear implant is beneficial to speech recognition and localization. The dynamic
test procedures used in this study illustrate the importance of bilateral hearing
for locating, identifying, and switching attention between multiple speakers. It is
recommended that unilateral cochlear implant recipients, with measurable unaided hearing
thresholds, be fit with a hearing aid.
Key Words
Bimodal hearing - cochlear implant - hearing aid - localization - speech recognition
