Abstract
The Nucleus® 5 System Sound Processor (CP810, Cochlear™, Macquarie University, NSW, Australia) contains two omnidirectional microphones. They can be configured as a fixed directional microphone combination (called Zoom) or as an adaptive beamformer (called Beam), which adjusts the directivity continuously to maximally reduce the interfering noise. Initial evaluation studies with the CP810 had compared performance and usability of the new processor in comparison with the Freedom™ Sound Processor (Cochlear™) for speech in quiet and noise for a subset of the processing options. This study compares the two processing options suggested to be used in noisy environments, Zoom and Beam, for various sound field conditions using a standardized speech in noise matrix test (Oldenburg sentences test). Nine German-speaking subjects who previously had been using the Freedom speech processor and subsequently were upgraded to the CP810 device participated in this series of additional evaluation tests. The speech reception threshold (SRT for 50% speech intelligibility in noise) was determined using sentences presented via loudspeaker at 65 dB SPL in front of the listener and noise presented either via the same loudspeaker (S0N0) or at 90 degrees at either the ear with the sound processor (S0NCI+) or the opposite unaided ear (S0NCI-). The fourth noise condition consisted of three uncorrelated noise sources placed at 90, 180 and 270 degrees. The noise level was adjusted through an adaptive procedure to yield a signal to noise ratio where 50% of the words in the sentences were correctly understood.In spatially separated speech and noise conditions both Zoom and Beam could improve the SRT significantly. For single noise sources, either ipsilateral or contralateral to the cochlear implant sound processor, average improvements with Beam of 12.9 and 7.9 dB in SRT were found. The average SRT of –8 dB for Beam in the diffuse noise condition (uncorrelated noise from both sides and back) is truly remarkable and comparable to the performance of normal hearing listeners in the same test environment. The static directivity (Zoom) option in the diffuse noise condition still provides a significant benefit of 5.9 dB in comparison with the standard omnidirectional microphone setting. These results indicate that CI recipients may improve their speech recognition in noisy environments significantly using these directional microphone-processing options.
Highlights
Introduction m CorrespondenceNorbert Dillier, Experimental Audiology, ENT Department, m University Hospital Zurich, Frauenklinikstrasse 24, CH-8091 Zurich, Switzerland.N manuscript preparation.Recipients of cochlear implants (CI) show remarkable speech recognition performance in quiet listening environments
The static directivity (Zoom) option in the diffuse noise condition still provides a significant benefit of 5.9 dB in comparison with the standard omnidirectional microphone setting
In some upgrade studies[6,8,15] of Freedom and CP810 processors sigous results for speech recognition in noisy and reverberant environments depending on the amount and configuration of hearing loss.[4] nificant performance differences were found for the Beam algorithm
Summary
Recipients of cochlear implants (CI) show remarkable speech recognition performance in quiet listening environments. Over the last 25 years, the results of word and sentence tests have continuously improved. A major factor of these improvements was attributed to more appropriate coding strategies and new sound processor technology as noted for example in a review paper1) where mean sentence recognition increased from 20% to 90% for the 22-electrode Nucleus system. Many authors did notice that speech understanding in noisy and reverberant environments still presents a major challenge for cochlear implant users.[2,3] Progress in digital signal processing
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