“Hey, I am here!” – quantifying localisation performance of cochlear implant users in difficult 
acoustic settings
S. Kerber and B. U. Seeber, MRC Institute of Hearing Research, University Park, Nottingham, UK
 
Cochlear implant (CI) users have problems with auditory localisation in reverberation and 
background noise. However, due to the degraded information provided by the implant correct 
localisation is an important means for helping to organise the auditory scene and thus aid 
understanding in difficult acoustic settings like group conversations. Thus, one aim of this study is 
to objectively quantify localisation performance of unilateral and bilateral CI users in difficult 
acoustic environments. Additionally, comparing performance across several tasks will help to 
understand how reverberation and noise affects binaural hearing with cochlear implants.

    We have developed a test battery which consists of different localisation tests, a speech test, a 
cognitive test and several questionnaires. All testing is done in the free-field using the “Simulated 
Open Field Environment” with participants pointing to the perceived sound location with a light 
pointer (Seeber et al., 2010). Test sounds where pulse-trains of uniform exciting noise and single 
words played from horizontal loudspeakers between -80° and 80°. 
    
    The localisation test battery consisted of four different localisation tests: In an inital test, 
localisation was assessed in quiet, anechoic conditions. Generally, performance of all bilateral 
cochlear implant users was good and superior to the performance of unilateral CI users. A second 
test assessed localisation in simulated rooms for different ratios of direct sound energy to 
reverberant energy (DRR). Reverberation affects localisation of words from +5 dB DRR with CIs 
while performance declines only below -7 dB DRR with normal hearing. This suggests that binaural 
localisation cues might not be available to CI listeners from speech in rooms. However, using pulse-
train stimuli one patient showed similar resistance against reverberation to normal-hearing 
participants, presumably due to using onset cues. Further two localisation tests looked into the 
disruption of localisation performance by one single reflection and by diffuse background noise, 
both presented at various levels. These two interferers emulate the early and late parts of room 
reverberation. Localisation of the bilateral CI user who showed good performance in reverberation 
was also less affected by a single reflection compared to his bilateral peers. However, in diffuse 
background noise all bilateral CI users lost localisation ability at signal-to-noise ratios of 0 dB where 
for normal hearing people only minor performance loss occurs. 

Acknowledgements 
This study was funded by the Intramural Programme of the Medical Research Council, UK and 
Cochlear Europe Ltd. 

References 
Seeber B.U., Kerber S. & Hafter E.R. (2010). A system to simulate and reproduce audio-visual 
environments for spatial hearing research. Hearing Research 260(1-2):1-10.