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.
