Binaural speech unmasking and interference in adult bilateral cochlear-implant users

Abstract

Bilateral cochlear implants (BICIs) provide improved speech perception in noise, primarily derived from the head-shadow benefit. BICI listeners can also demonstrate binaural speech unmasking or squelch, particularly if the interferer is a single other speaker. However, under the same conditions, some BICI listeners can experience interference. This study tested 21 adult BICI listeners on speech understanding using a range of masker conditions (1, 2, 3, or 4 same-sex talkers, speech-modulated noise, or speech-shaped stationary noise). For listeners that showed binaural unmasking, the amount of unmasking was highest for the one-talker condition and least for the stationary noise, decreasing as the number of interfering talkers increased and the envelope modulation depth decreased. For listeners that showed interference, there were mainly two types of interference patterns: (1) where the amount of interference varied idiosyncratically across masker type, and (2) any stimulation in one ear essentially produced chance performance in the other ear for all masker conditions. The latter interference pattern occurred for the listeners with the largest asymmetries in speech understanding. This suggests, in these extreme cases, a possible central cortical processing bias for one ear and a more equal speech understanding between the ears may diminish interference.