Binaural Interaction and Auditory Stream Segregation in Adults with Sequential Bilateral Cochlear Implants

Background:

An increasing number of patients receive a second cochlear implant (CI). CI electrode arrays often differ in the two ears and their fitting may be performed without specific considerations for binaural cues. In sound localization and speech-in-noise tests, both requiring binaural temporal processing, bilateral CI users exhibit a wide variability. This variance can only partly be explained by patient-specific factors or the interventions with CIs. Rapid temporal processing, which has been shown to be limited in CI recipients, may be studied in bilateral CI users with a binaurally presented auditory stream segregation test.

Objective:

The aim of this study was to investigate auditory stream segregation in sequentially implanted adults and in age- and gender-matched normal-hearing subjects.

Methods:

Triplet ABA-ABA- pattern tone sequences were presented pseudo-randomly. A (408 Hz) and B (either 854, 1638 or 4090 Hz) were delivered to the different ears. Temporal coherence and fission boundaries were measured as sound onset asynchronies (SOA, ms) in a two-alternative forced-choice task via an adaptive test procedure.

Results:

The initial results show that the mean SOA was statistically significantly (p < 0.05) larger for the CI recipients (209 ms) than for the normally-hearing control group (119 ms).

Conclusions:

According to the initial results, in bilaterally implanted CI users the stream segregation occurs with significantly slower stimulus rates than in normal-hearing subjects. The ultimate aim is to correlate these findings with sound localization abilities, speech understanding in noise, and binaural interaction assessed via electrically-evoked auditory brainstem responses.