Simulation of unilateral and bilateral cochlear implants on spatial speech-in-noise tasks

The current study simulated bilateral and unilateral cochlear implant (CI) processing using a channel vocoder with dense tonal carriers ("SPIRAL") in 13 normal-hearing listeners. Their performance of recognizing spatial speech-in-noise was measured under the effects of three masker locations (0°, +90°, and -90°; target at 0°) and three types of maskers (steady-state noise, speech-modulated noise, and a single-talker interferer) where the maskers contained different levels of energetic and informational masking. The stimuli were spatialized using the head-related impulse responses recorded from behind-the-ear microphones of hearing aids. The results showed that simulated users of bilateral CIs displayed binaural benefits (i.e., binaural summation and binaural squelch) in the maskers with pure energetic masking or with additional modulation masking but not in the masker with primarily language-based informational masking. Binaural benefits observed in the simulation did not consistently agree with the findings in real CI users. The use of SPIRAL vocoder allows further parameterization research into pinning down the factors that affect binaural benefits in bilateral CIs.