Spatial advantage in bilateral cochlear implant recipients using a spatially-symmetric speechon-speech masker paradigm.

Having access to the signals at the two ears is important for understanding speech in noisy conditions. One of the contributing mechanisms is better-ear glimpsing (BEG), which takes advantage of the fluctuating signal-to-noise ratios (SNRs) across ears. Even though the spatial benefit provided by bilateral (over unilateral) implantation has been studied widely, the benefit provided by BEG is still poorly understood. Therefore, speech comprehension performance was measured in ten bilateral CI users in a spatially-symmetric masker paradigm. Helen-like questions recorded with a female native English speaker were presented from a loudspeaker in front of the subject (0o) while two female speech distractors were presented either from loudspeakers at ±90o or co-located with the target questions. The subjects' task was to answer the questions. The combined distractor level was kept constant at 60 dBSPL and the level of the target questions was varied adaptively to obtain speech comprehension thresholds (SCTs), i.e., the SNR at which 50% of the questions were answered correctly. SCTs were measured unilaterally and bilaterally. The spatial benefit was calculated as the difference in SCTs between the spatially-separated and co-located condition for bilateral stimulation. The average benefit was 2 dB with individual results varying from -2 to 7 dB. The bilateral benefit was calculated as the difference in SCTs between bilateral and unilateral stimulation in the spatially- separated condition. The average bilateral benefit was 1.4 dB when compared to the better ear and 5.9 dB when compared to the worse ear. Individual results varied from -2.5 to 5 dB and 1.9 to 12.7 dB, respectively. Hence, bilateral CI users can benefit significantly from a second device in spatially-symmetric, fluctuating noise where neither of the ears receives a constant favorable SNR. Future research should further investigate the large inter-subject variability and further improve the observed benefits. [ABSTRACT FROM AUTHOR]