Binaural speech unmasking and localization in noise with bilateral cochlear implants using envelope and fine-timing based strategies

Abstract

Four adult bilateral cochlear implant users, with good open-set sentence recognition, were tested with three different sound coding strategies for binaural speech unmasking and their ability to localize 100 and 500 Hz click trains in noise. Two of the strategies tested were envelope-based strategies that are clinically widely used. The third was a research strategy that additionally preserved fine-timing cues at low frequencies. Speech reception thresholds were determined in diotic noise for diotic and interaurally time-delayed speech using direct audio input to a bilateral research processor. Localization in noise was assessed in the free field. Overall results, for both speech and localization tests, were similar with all three strategies. None provided a binaural speech unmasking advantage due to the application of 700 micros interaural time delay to the speech signal, and localization results showed similar response patterns across strategies that were well accounted for by the use of broadband interaural level cues. The data from both experiments combined indicate that, in contrast to normal hearing, timing cues available from natural head-width delays do not offer binaural advantages with present methods of electrical stimulation, even when fine-timing cues are explicitly coded.

Effect of mismatched place-of-stimulation on binaural fusion and lateralization in bilateral cochlear-implant users

“…Briefly, SRM is the improvement in speech-in-noise understanding gained from a spatial separation between a target talker and maskers, and has been shown to be significantly lower and highly variable in CI users compared to NH subjects, for both adults (Loizou et al, 2009) and children . Although better ear listening accounts for much of the deficit in the benefit from SRM in CI users (van Hoesel et al, 2008;Loizou et al, 2009;Aronoff et al, 2011;Culling et al, 2012), it is likely that interaural frequency mismatch, among other factors, may explain why performance in CI users is unable to surpass that of better ear listening. One might hypothesize that in the absence of ITDs and ILDs, a small amount of mismatch can cause a frontal sound source to be perceived lateralized to one side.…”

Head orientation benefit to speech intelligibility in noise for cochlear implant users and in realistic listening conditions

“…Despite all the recent efforts made to restore access to interaural time delays at low frequencies, BCI users exhibit negligible binaural unmasking and pitch cues are limited by the relatively sparse encoding of sound by CIs. As a result, CI users only benefit from head-shadow and lip-reading benefit effects, binaural unmasking being inaccessible (Churchill et al, 2014;Van Hoesel et al, 2008) and discrimination of voice fundamental frequencies very limited (Carroll and Zeng, 2007;Geurts and Wouters, 2004). Dip-listening is also much harder for CI users (Nelson et al, 2003).…”

Sensitivity to interaural envelope correlation changes in bilateral cochlear-implant users

“…In an attempt to transition from studying binaural unmasking of tones to using speech signals, van Hoesel et al (2008) measured binaural unmasking of tones and speech with NoS(s ¼ 0.7 ms) for four bilateral CI listeners using synchronized research processors. They tested two speech processing strategies, one that discarded finestructure timing cues and one that explicitly encoded finestructure timing cues, which was called peak-derived timing.…”