ABSTRACT
Binaural notched-noise experiments indicate a reduced frequency selectivity of the binaural system compared to monaural processing. The present study investigates how auditory efferent activation (via the medial olivocochlear system) affects binaural frequency selectivity in normal-hearing listeners. Thresholds were measured for a 1-kHz signal embedded in a diotic notched-noise masker for various notch widths. The signal was either presented in phase (diotic) or in antiphase (dichotic), gated with the noise. Stimulus duration was 25 ms, in order to avoid efferent activation due to the masker or the signal. A bandpass-filtered noise precursor was presented prior to the masker and signal stimuli to activate the efferent system. The silent interval between the precursor and the masker-signal complex was 50 ms. For comparison, thresholds for detectability of the masked signal were also measured in a baseline condition without the precursor and, in addition, without the masker. On average, the results of the baseline condition indicate an effectively wider binaural filter, as expected. For both signal phases, the addition of the precursor results in effectively wider filters, which is in agreement with the hypothesis that cochlear gain is reduced due to the presence of the precursor.
Subject(s)
Auditory Pathways/physiology , Efferent Pathways/physiology , Pitch Perception , Acoustic Stimulation , Adult , Auditory Threshold , Cochlea/physiology , Female , Humans , Male , Middle Aged , Noise/adverse effects , Olivary Nucleus/physiology , Perceptual Masking , Psychoacoustics , Signal Detection, Psychological , Time Factors , Young AdultABSTRACT
OBJECTIVE: Compare speech performance in noise with matched bilateral cochlear implant (CICI) and unilateral cochlear implant (CI only) users. DESIGN: Thirty CICI and 30 CI-only subjects were tested on a battery of speech perception tests in noise that use an eight-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 with the CI-only subjects, supporting the hypothesis that CICI is more beneficial than CI only.
