Head Shadow and Binaural Squelch for Unilaterally Deaf Cochlear Implantees

Background: Cochlear implants (CIs) can improve speech-in- noise performance for listeners with unilateral sensorineural deafness. But these benefits are modest and in most cases are limited to head-shadow advantages, with little evidence of binaural squelch. Hypothesis: The goal of the investigation was to determine whether CI listeners with normal hearing or moderate hearing loss in the contralateral ear would receive a larger head-shadow benefit for target speech and noise originating from opposite sides of the head, and whether listeners would experience binaural squelch in the free field in a test involving interfering talkers. Methods: Eleven CI listeners performed a speech-identification task in the presence of interfering noise or speech. Six listeners had single-sided deafness (normal or near-normal audiometric thresholds in the acoustic ear) and five had asymmetric hearing loss (hearing loss in the acoustic ear treated with a hearing aid). Listeners were tested with the acoustic ear only and bilaterally with the CI turned on. One set of conditions examined head-shadow effects with target speech and masking noise presented from azimuths of 0 or +/- 108 degrees. A second set of conditions examined binaural squelch, with target speech presented from the front and interfering talkers symmetrically placed on both sides. Results: On average, the largest head-shadow benefit (5 dB) occurred when the target and masking noise were presented on opposite sides of the head. Listeners also showed an average of 2dB of squelch, but only when the target speech was masked by interfering talkers of the same sex as the target. Conclusions: CIs provide listeners with unilateral deafness important benefits for speech perception in complex spatial environments, including a larger head-shadow benefit when speech and noise originate on opposite sides of the head, and an improved ability to perceptually organize an auditory scene with multiple competing voices.