Abstract
Background:
Sentence understanding scores for patients with cochlear implants (CIs) when tested
in quiet are relatively high. However, sentence understanding scores for patients
with CIs plummet with the addition of noise.
Purpose:
To assess, for patients with CIs (MED-EL), (1) the value to speech understanding of
two new, noise-reducing microphone settings and (2) the effect of the microphone settings
on sound source localization.
Research Design:
Single-subject, repeated measures design. For tests of speech understanding, repeated
measures on (1) number of CIs (one, two), (2) microphone type (omni, natural, adaptive
beamformer), and (3) type of noise (restaurant, cocktail party). For sound source
localization, repeated measures on type of signal (low-pass [LP], high-pass [HP],
broadband noise).
Study Sample:
Ten listeners, ranging in age from 48 to 83 yr (mean = 57 yr), participated in this
prospective study.
Intervention:
Speech understanding was assessed in two noise environments using monaural and bilateral
CIs fit with three microphone types. Sound source localization was assessed using
three microphone types.
Data Collection and Analysis:
In Experiment 1, sentence understanding scores (in terms of percent words correct)
were obtained in quiet and in noise. For each patient, noise was first added to the
signal to drive performance off of the ceiling in the bilateral CI-omni microphone
condition. The other conditions were then administered at that signal-to-noise ratio
in quasi-random order. In Experiment 2, sound source localization accuracy was assessed
for three signal types using a 13-loudspeaker array over a 180° arc. The dependent
measure was root-mean-score error.
Results:
Both the natural and adaptive microphone settings significantly improved speech understanding
in the two noise environments. The magnitude of the improvement varied between 16
and 19 percentage points for tests conducted in the restaurant environment and between
19 and 36 percentage points for tests conducted in the cocktail party environment.
In the restaurant and cocktail party environments, both the natural and adaptive settings,
when implemented on a single CI, allowed scores that were as good as, or better, than
scores in the bilateral omni test condition. Sound source localization accuracy was
unaltered by either the natural or adaptive settings for LP, HP, or wideband noise
stimuli.
Conclusion:
The data support the use of the natural microphone setting as a default setting. The
natural setting (1) provides better speech understanding in noise than the omni setting,
(2) does not impair sound source localization, and (3) retains low-frequency sensitivity
to signals from the rear. Moreover, bilateral CIs equipped with adaptive beamforming
technology can engender speech understanding scores in noise that fall only a little
short of scores for a single CI in quiet.
Key Words
beamforming - cochlear implants - R-Space™ - speech perception in noise
