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

Abstract

In Brief Objective: 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. Design: 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. Results: 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. Conclusions: 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. The impact of bilateral cochlear implant use on speech perception in noise in 21 bilateral users of the MED-EL COMBI 40/40+ cochlear implants. Speech reception thresholds were measured using the Oldenburg sentence test. Speech was presented from the front. Noise was either presented from the front, or from the left side, or from the right side. Each condition was measured for unilateral and bilateral implant use. The 18 subjects from which 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. Bilateral CI users can at least qualitatively benefit from the effects which are known from ‘normal hearing’ subjects, i.e., head shadow, summation, and squelch effect.