Introduction Interaction between acoustic and electrical stimulation in bimodal patients is of
major interest as it mainly influences speech understanding in everyday situations.
Contralateral suppression is an important strategy in binaural hearing: If noise is
presented to one ear, efferent signals of the contralateral Nucleus olivaris medialis
are provided to inhibit input of the noise-related ear. Mechanisms of contralateral
suppression in patients with a hearing aid (HA) in one ear and a cochlear implant
(CI) in the other have not yet been investigated.
Methods Calibration of acoustic and electrical suppression signal was completed by testing
healthy volunteers. Experimental setup for bimodal patients was established: E-BERA
(click) on CI was deducted while playing an acoustic suppression signal on HA side,
in a second module an acoustic BERA (click) was deducted on HA side while playing
an electrical suppression signal on CI side. Speech understanding in quiet and in
noise was assessed.
Results An increase of wave V potential was determined when an electrical suppression signal
was presented on the contralateral CI side. The results could be reproduced. In patients
with a good performance of speech understanding in quiet and noise this effect seems
to be more distinct. Preoperative duration of deafness seems to influence measurement
outcomes.
Conclusion The experimental setup presented in this study can be used to measure contralateral
suppression in bimodal provided patients. Although bimodal patients have to cope with
differed aural input binaural interactions remain crucial for hearing outcome in quiet
and noise. Duration of deafness and degree of hearing loss on HA side seem to be important
factors of contralateral suppression.
