Head Shadow, Squelch, and Summation Effects in Bilateral Users of the MED-EL COMBI 40/40+ Cochlear Implant

TLDR

The study aimed to assess how bilateral MED‑EL COMBI 40/40+ cochlear implants affect speech perception in noise among bilateral users. Speech reception thresholds were measured with the Oldenburg sentence test in 21 subjects, presenting speech from the front and noise from front, left, or right, and comparing unilateral and bilateral implant conditions (three participants were excluded due to difficulty). Bilateral users showed significant head‑shadow (6.8 dB) and summation (2.1 dB) effects across all conditions, a squelch effect (0.9 dB) only for left‑side noise, and overall performance approached that of normal‑hearing listeners, with effect sizes unrelated to deafness duration.

Abstract

The aim of the study was to investigate the impact of bilateral cochlear implant use on speech perception in noise in bilateral users of the MED-EL COMBI 40/40+ cochlear implants.Speech reception thresholds were measured in 21 subjects using the Oldenburg sentence test. Speech was always presented from the front. Noise was either presented from the front, from the left side, or from the right side. Each condition was measured for unilateral and bilateral implant use.For three subjects, the test was too difficult to be administered. The 18 subjects from whom a complete data set could be obtained showed a significant head shadow effect and summation effect for all test conditions, whereas the squelch effect was significant for noise from the left side only. Average effect sizes were significant for all effects and amounted to 6.8 dB for the head shadow effect, 0.9 dB for the squelch effect, and 2.1 dB for the summation effect. Effect sizes were not correlated with duration of deafness.Bilateral cochlear implant users can at least qualitatively benefit from the effects that are known from normal-hearing subjects, that is, head shadow, summation, and squelch effect. Bilateral cochlear implantation also reduces the performance gap between cochlear implant users and normal-hearing subjects.