Localisation with bilateral cochlear implants in reverberant environments 

Bernhard Seeber

MRC Institute of Hearing Research, Nottingham, UK


Cochlear implants (CIs) often restore speech understanding in quiet, but most 
patients complain that the presence of reverberation or noise makes understanding 
of speech more difficult or even impossible. In normal hearing, a spatial 
separation between target and noise source helps speech understanding. The ability 
to localise the target is closely linked to it and often similarly impaired by the 
presence of noise. 

We will review the ability of patients with bilateral CIs to localise single sound 
sources which can be remarkably good. We will report on a study that investigated 
the effect of reflections on localisation ability. In normal hearing, the 
precedence effect allows for unimpaired localisation of the leading sound source 
despite the presence of later arriving reflections. Our results with bilateral CI-
listeners show two main outcomes: (1) About half of the tested patients showed no 
precedence effect; instead a single sound source was localised in-between the 
leading and the lagging source; (2) A few patients showed the precedence effect 
even for temporally overlapping stimuli. This is remarkable for two reasons: (1) 
It requires access to binaural information of the lead despite a strong waveform 
interaction with the lag; (2) Fine temporal cues are not encoded in the electric 
pulses in current CIs but this information is crucial for the precedence effect in 
normal hearing. The results suggest that CI-listeners instead used different 
information.