Objective Compare speech performance in noise with matched bilateral (CICI) and unilateral (CI-Only) cochlear implant users. Design Thirty CICI and 30 CI-Only subjects were tested on a battery of speech perception tests in noise that utilize an 8-loudspeaker array. Results On average, CICI subject's performance with speech in noise was significantly better than the CI-Only subjects. Conclusion The CICI group showed significantly better performance on speech perception in noise compared to the CI-Only subjects, supporting the hypothesis that bilateral cochlear implantation is more beneficial than unilateral implantation.

Abbreviations: ERB, equivalent rectangular bandwidth; MOC, medial olivocochlear.Running title: Efferent effect on binaural processing Verhey et al. 2ABSTRACT 1 2 Binaural notched-noise experiments indicate a reduced frequency selectivity of the 3 binaural system compared to monaural processing. The present study investigates how 4 auditory efferent activation (via the medial olivocochlear system) affects binaural 5 frequency selectivity in normal-hearing listeners. Thresholds were measured for a 1-6 kHz signal embedded in a diotic notched-noise masker for various notch widths. The 7 signal was either presented in phase (diotic) or in antiphase (dichotic), gated with the 8 noise. Stimulus duration was 25 ms, in order to avoid efferent activation due to the 9 masker or the signal. A bandpass-filtered noise precursor was presented prior to the 10 masker and signal stimuli to activate the efferent system. The silent interval between 11 the precursor and the masker-signal complex was 50 ms. For comparison, thresholds 12 for detectability of the masked signal were also measured in a baseline condition 13 without the precursor and, in addition, without the masker. On average, the results of 14 the baseline condition indicate an effectively wider binaural filter, as expected.

The objective of the study is to assess the hearing performance of cochlear implant users in three device microphone configurations: omni-directional, directional, and beamformer (BEAMformer two-adaptive noise reduction system), in localization and speech perception tasks in dynamically changing listening environments. Seven cochlear implant users aided with Cochlear CM-24 devices with Freedom speech processor participated in the study. For the localization test in quiet and in background noise, subjects demonstrated significant differences between different microphone settings. Confusion matrices showed that in about 70% cases cochlear implant subjects correctly localized sounds within a horizontal angle of 30-40• (±1 • loudspeaker apart from signal source). However localization in noise was less accurate as shown by a large number of considerable errors in localization in the confusion matrices. Average results indicated no significant difference between three microphone configurations. For speech presented from the front 3 dB SNR improvements in speech intelligibility in three subjects can be observed for beamforming system compared to directional and omni-directional microphone settings. The benefits of using different microphone settings in cochlear implant devices in dynamically changing listening conditions depend on the particular sound environment.

Loudness functions and binaural loudness summation was investigated in acoustically stimulated bilaterally implanted cochlear implant users. The study was aimed at evaluating growth of loudness functions and binaural loudness summation in cochlear implant subjects as a function of stimulus presentation level at different frequencies. Loudness was assessed using a rating procedure on a scale of 0 to 100. Three experimental conditions were tested: monaural right, monaural left and binaural, each with bands of noise with center frequencies of 0.25, 1, and 4 kHz. Fifteen implanted and five normal-hearing subjects (control group) participated in the experiments. Results demonstrated large variability in the slopes of the loudness functions and the presence of loudness summation in bilateral cochlear implant users, with large individual differences among subjects.

The present study investigates how diotic and dichotic masked thresholds, in a notched-noise masking paradigm, are affected by activation of the Medial OlivoCochlear (MOC) reflex. Thresholds were obtained for a 500-Hz pure tone diotic or a dichotic signal, S (S0 or Sπ respectively), in the presence of a simultaneous or forward diotic masker (bandpass noise with no notch or a 400-Hz notch). A diotic precursor sound (bandpass noise with a 400- or 800-Hz notch) was presented prior to the signal and masker to activate the MOC reflex. For simultaneous- and forward-masking conditions, the decrease in masked thresholds as a notch was introduced in the masker was larger for the diotic than for the dichotic condition. This resulted in a reduced binaural masking level difference (BMLD) for the masker with a notch. The precursor augmented these two effects. The results indicate that the effect of the precursor, eliciting the MOC reflex, is less pronounced when binaural cues are processed.