No Squelch Effect After Sequential Bilateral Cochlear Implantation in Postlingually Deafened Adults: Is There a First Ear Advantage?

Objectives: To investigate whether a squelch effect develops in postlingually deafened adults after sequential bilateral cochlear implantation.

Study Design: Prospective study as part of a randomized controlled trial on the difference between simultaneous versus sequential bilateral cochlear implantation.

Setting: Tertiary referral center.

Participants: Sixteen postlingually deafened adults.

Intervention: Sequential bilateral cochlear implantation with a 2-year interimplant interval.

Main Outcome Measure: A squelch effect was defined as a better bilateral score than unilateral score on a speech-intelligibility-in-noise test with spatially separated sources. The squelch effect was evaluated for the participants' best performing cochlear implant (CI) ear, the left CI in the condition with speech from -60 degrees azimuth and noise from +60 degrees azimuth (S-60 N+60), the right CI (N-60 S+60), CI1 and CI2. Evaluations took place 1, 2 and median 4 years after sequential implantation.

Results: No significant squelch effect was found, except for the right CI (N-60 S+60) after 2 years. No differences in speech perception-in-noise from straight ahead were seen between CI1 and CI2. Comparing performance of participants whose better or worse ear was implanted first did not reveal differences either. For the best performing situation, 7/16, 6/16, and 3/12 participants exhibited a squelch effect after 1, 2, and 4 years of follow-up.

Conclusions: Participants who underwent sequential bilateral cochlear implantation with a 2-year interimplant interval did not develop an evident squelch effect on group level after a median follow-up of 4 years. Individual participants were able to make use of the squelch effect. The less evident squelch effect is at odds with our group of simultaneously implanted bilateral cochlear implant users. Neither a difference between CI1 and CI2, nor implanting the better or worse ear first could explain the less evident squelch effect in these patients.

Trial Registration: Dutch Trial Register NTR1722.