Localisation performance with cochlear implants in simulated rooms

Stefan Kerber and Bernhard U. Seeber

MRC Institute of Hearing Research
Science Road, University Park
Nottingham
NG7 2RD
United Kingdom


Background
Cochlear implant patients commonly report problems localising sounds in rooms. 
While this is partly due to their generally poor localisation ability, our 
preliminary studies suggest that sound reflections from room boundaries may 
exacerbate the problem. Normal hearing people, instead, are able to largely 
ignore reflections when localising sounds. The present study examines 
localisation performance of cochlear implant patients in simulated realistic 
rooms. Localisation ability is quantified for realistic conditions and the 
tolerable amount of reverberation is assessed which might have implications 
for the design of new classrooms.

Methods
A setup of 48 loudspeakers in an anechoic chamber was used to synthesise the 
sound field of a realistic room. Reflection patterns for sound sources at 
eleven directions in the frontal hemifield of a listener were calculated. 
Target sounds and reflections were played from individual loudspeakers in 
such a way that spectral, temporal and, most importantly, spatial properties 
of each reflection were like in a real room. Using these simulations, sounds 
were presented at varying levels of reverberation, i.e. direct-to-reverberant 
ratios.  After each presentation, participants had to position a light spot 
to the perceived direction of the sound.

Results
Preliminary results of unilateral cochlear implant patients show highly 
increased sensitivity to reflections of realistic rooms. At a 
direct-to-reverberant ratio of -3 dB, where normal hearing participants show 
no impairment of localisation, a patient with a single cochlear implant showed 
a roughly twofold increase of interquartile ranges compared to anechoic 
conditions and more than 70 % of frontal sounds were perceived in the back. 
Investigations with bilateral cochlear implant patients are ongoing and latest 
results will be presented at the conference. 

Conclusion
Cochlear implant patients show increased sensitivity to room reflections which 
should be considered when designing class-rooms for teaching children with 
cochlear implants.