Effects of directional microphone and adaptive multichannel noise reduction algorithm on cochlear implant performance

Abstract

Although cochlear implant ͑CI͒ users have enjoyed good speech recognition in quiet, they still have difficulties understanding speech in noise. We conducted three experiments to determine whether a directional microphone and an adaptive multichannel noise reduction algorithm could enhance CI performance in noise and whether Speech Transmission Index ͑STI͒ can be used to predict CI performance in various acoustic and signal processing conditions. In Experiment I, CI users listened to speech in noise processed by 4 hearing aid settings: omni-directional microphone, omni-directional microphone plus noise reduction, directional microphone, and directional microphone plus noise reduction. The directional microphone significantly improved speech recognition in noise. Both directional microphone and noise reduction algorithm improved overall preference. In Experiment II, normal hearing individuals listened to the recorded speech produced by 4-or 8-channel CI simulations. The 8-channel simulation yielded similar speech recognition results as in Experiment I, whereas the 4-channel simulation produced no significant difference among the 4 settings. In Experiment III, we examined the relationship between STIs and speech recognition. The results suggested that STI could predict actual and simulated CI speech intelligibility with acoustic degradation and the directional microphone, but not the noise reduction algorithm. Implications for intelligibility enhancement are discussed.

Two-microphone spatial filtering provides speech reception benefits for cochlear implant users in difficult acoustic environments

“…For example, Chung et al (2006) reported a 3.5 dB benefit for a hypercardioid directional over an omni-directional microphone. One source of the higher Dipole relative to Omni SRT benefit observed here might be the particular interaction of noise source location with the dipole-microphone directional response.…”

“…One source of the higher Dipole relative to Omni SRT benefit observed here might be the particular interaction of noise source location with the dipole-microphone directional response. Chung et al (2006) evaluated beamformers using a noise field generated by playing uncorrelated noise from 8 speakers at 0 , 45 , 90 , 135 , 180 , 225 , 270 , and 315 . In this case, no particular loudspeaker was positioned exactly at either of the theoretical free-field hypercardioid azimuthplane null locations (120 and 240 ).…”

“…The output SNR of a multiple-microphone array can be increased using a linear, time-invariant, combination of the microphone signals. Such fixed-processing beamformers have been demonstrated as effective noise reduction solutions for CIs (Chung et al, 2004(Chung et al, , 2006Chung and Zeng, 2009).…”

Reducing the impact of wind noise on cochlear implant processors with two microphones

“…In a directional design microphones are sensitive toward sounds emanating from the front and attenuate sounds originating outside the desired pickup area (Chung, 2004;Chung et al, 2006). The Nucleus 5 CP810 device uses two closely spaced and matched omni-directional microphones (front and rear).…”

A Dual-Microphone Algorithm That Can Cope With Competing-Talker Scenarios

“…Fixed and adaptive (software or hardware) directional microphones as well as beamforming algorithms have been extensively investigated during the past two decades [5]. In [6], an overall improvement of 3-5 dB has been reported by directional microphones in comparison to processing with omnidirectional microphones, for tests with CI users in low reverberation environments. A detailed overview of fixed and adaptive directional microphones can be found in [5].…”