When having two ears produces interference instead of a speech-perception advantage

Joshua Bernstein, Walter Reed National Military Medical Center

Abstract

Having two ears is highly beneficial, which is why bilateral cochlear implants (BI-CIs, a CI in each ear) and single-sided-deafness CIs (SSD-CIs, one normal-hearing and one CI ear) are becoming more common. BI-CIs and SSD-CIs provide clear benefits for spatial hearing but with large outcome variability. We have identified a key factor— “contralateral speech interference”—that might contribute to variability in speech understanding in competing-talker situations by reducing the head-shadow benefit that have hearing in both ears would otherwise provide. Interference is revealed by a paradigm designed to examine binaural integration for CI speech perception. In the monaural condition, target and interfering speech are presented to one ear. In the bilateral condition, a copy of the interfering speech is also presented to the other ear. 

This talk will overview a series of studies that reveal tremendous differences across listener groups and individuals in the extent to which presenting a copy of the masker to a second auditory input influences performance. In some cases, adding the second ear improves speech perception (contralateral unmasking). Contralateral unmasking is most likely to occur when target speech is presented to an acoustic or electric ear with good monaural intelligibility. In other cases, adding the second ear reduces performance (contralateral interference), sometimes so dramatically as to nearly extinguish any speech perception in the target ear. Contralateral interference is most likely to occur when the target ear has relatively poor monaural intelligibility or the contralateral ear has high monaural intelligibility. For example, this occurs for SSD-CI users attending to their CI ear, or for BI-CI users with a long duration of deafness in the target CI ear. Thus, while some CI listeners can benefit from having two ears to perceptually organize the auditory scene, others are instead susceptible to contralateral interference effects. In everyday communication settings, this means that while having two ears may provide a head-shadow benefit, interference could reduce this advantage when multiple people are speaking.

The talk will conclude by touching on some of our early efforts and plans to understand the underlying causes of contralateral interference. For example, does interference reflect a general, aging-related “selective-attention” deficit (difficulty attending to target speech while ignoring an interferer) or if it is specific to experience with asymmetric hearing? Does interference stem directly from asymmetric distortion in peripheral nerve responses, or does it reflect central maladaptive changes? We will welcome workshop participants to suggest their own ideas for techniques and approaches that might be used to better understand this phenomenon that is likely to limit clinical outcomes for a growing population of CI users with hearing in both ears.

[Funding: NIH-NIDCD R01-DC-015798 (Bernstein/Goupell). The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army/Navy/Air Force, Department of Defense, or U.S. Government.]