Impact of Bilateral Hearing on Release from Cognitive Load and Release from Masking

Patients with bilateral deafness are eligible to receive bilateral cochlear implants (BiCIs), and in some countries, patients who suffer from single-sided deafness are receiving a cochlear implant (SSD-CI) in the deaf ear. In both the BiCI and SSD-CI populations there is a potential benefit from the integration of inputs arriving from both ears. One of the demonstrated benefits is improved sound localization. A second known benefit is improved ability to segregate speech from background noise or competing maskers. When speech and maskers are spatially separated vs. co-located, listeners’ benefit is measured as ‘spatial release from masking’ (SRM: improvement in speech understanding in relation to the separated condition). SRM depends on many factors, including the location of the maskers relative to the ‘better’ vs. ‘poorer’ ear. We study cognitive load by measuring real-time pupil dilation as a means to assess listening effort while subjects listen to speech stimuli. We are interested in the extent to which bilateral hearing and SSD-CI hearing may promote spatial release from masking, while reducing cognitive load. Alternatively, bilateral and SSD-CI hearing might result in release from masking but promote increased cognitive load. The latter might occur if the added ear provides information that is useful for spatial hearing but is difficult to comprehend. By understanding the cost/benefit of integrating inputs to two ears, a more complete picture of the advantages of bilateral stimulation can emerge.

Work funded by grants from NIH-NIDCD (5 R01 DC003083, to RYL), with partial support for the SSD-CI study from MED-EL.