Echo suppression with cochlear implants - What can we learn from
simulations? 

B. Seeber, Auditory Perception Lab, Dept. of Psychology, UC
Berkeley, Berkeley, CA and MRC Institute of Hearing Research,
University Park, Nottingham, UK 

This poster will present an overview of our results on the
precedence effect with bilateral cochlear implants (CIs) and relate
them to results obtained from vocoder simulations. Using current
devices CI-subjects have very limited access to interaural time
differences (ITDs) and spectral information while interaural level
cues and the temporal envelope are relatively well reproduced. This
information is sufficient for localization in quiet but we question
if the presence of reflections would disturb it. A study of
localization dominance with bilateral CI-subjects revealed that
some subjects show precedence, i.e. echo suppression, as
localization of a single, fused image at the lead similar to normal
hearing. Surprisingly, some subjects even showed precedence for
ongoing speech sounds. However, other CI-subjects fused lead and
lag, but the image was not localized at the lead.  

Using a noise-band vocoder CI-simulation we studied how normal
hearing subjects localize the precedence stimuli when ITDs are not
encoded in the carrier. We found that the precedence-effect was
disturbed for ongoing sounds and lead and lag were each heard
separately (Seeber and Hafter, 2007). Increasing the amount of
temporal information in the envelope did not lead to precedence.
However, ongoing study shows that modification of the spectral
match of the carriers might induce precedence even without encoding
ITD-information in the carrier. 

Acknowledgements
Support was thankfully provided by NIH RO1DCD00087, NOHR 018750,
and the MRC. 

References
Seeber, B. and E. Hafter, "Precedence-effect with cochlear implant
simulation", In: B. Kollmeier, G. Klump, V. Hohmann, U. Langemann,
M. Mauermann, S. Uppenkamp and J. Verhey: "Hearing - from Sensory
Processing to Perception", Springer, Berlin, Heidelberg, chapter
51, pg. 475-484, 2007.