Speech intelligibility by bilateral cochlear implant users when interaural level cues are made more consistent across frequency

Abstract

Interaural level differences (ILDs) aid speech understanding for listeners with both normal hearing (NH) and bilateral cochlear implants (BCIs). Naturally-occurring ILDs are less than ideal for this outcome; however, as they are generally restricted to frequencies above about 2000 Hz, while the energy in speech is typically concentrated below 2 kHz. It has recently been demonstrated that applying larger-than-normal ILDs in the low-frequency region can significantly improve speech intelligibility for BCI users. Despite the benefit, this may result in sound sources that appear to move, depending on where in frequency the speech energy resides at a given moment. The current study examined the effect of applying larger-than-normal ILDs both above and below 2 kHz. Speech intelligibility was measured in simulation by 16 individuals with NH, and by eight BCI users, of a target talker along the midsagittal plane in the presence of symmetrically placed masker talkers on either side. An improvement of about 20 perc...