Advantages from bilateral hearing in speech perception in noise with simulated cochlear implants and residual acoustic hearing

Acoustic simulations were used to study the contributions of spatial hearing that may arise from
combining a cochlear implant with either a second implant or contralateral residual low-frequency
acoustic hearing. Speech reception thresholds (SRTs) were measured in twenty-talker babble.
Spatial separation of speech and noise was simulated using a spherical head model. While
low-frequency acoustic information contralateral to the implant simulation produced substantially
better SRTs there was no effect of spatial cues on SRT, even when interaural differences were
artificially enhanced. Simulated bilateral implants showed a significant head shadow effect, but no
binaural unmasking based on interaural time differences, and weak, inconsistent overall spatial
release from masking. There was also a small but significant non-spatial summation effect. It appears
that typical cochlear implant speech processing strategies may substantially reduce the utility of
spatial cues, even in the absence of degraded neural processing arising from auditory deprivation.