Evaluation of different signal processing options in unilateral and bilateral cochlear freedom implant recipients using R-Space background noise

Abstract

Background: Difficulty understanding in background noise is a common complaint of cochlear implant (CI) recipients. Programming options are available to improve speech recognition in noise for CI users including automatic dynamic range optimization (ADRO), autosensitivity control (ASC), and a two-stage adaptive beamforming algorithm (BEAM). However, the processing option that results in the best speech recognition in noise is unknown. In addition, laboratory measures of these processing options often show greater degrees of improvement than reported by participants in everyday listening situations. To address this issue, Compton-Conley and colleagues developed a test system to replicate a restaurant environment. The R-SPACE™ consists of eight loudspeakers positioned in a 360 degree arc and utilizes a recording made at a restaurant of background noise.

Purpose: The present study measured speech recognition in the R-SPACE with four processing options: standard dual-port directional (STD), ADRO, ASC, and BEAM.

Research design: A repeated-measures, within-subject design was used to evaluate the four different processing options at two noise levels.

Study sample: Twenty-seven unilateral and three bilateral adult Nucleus Freedom CI recipients.

Intervention: The participants' everyday program (with no additional processing) was used as the STD program. ADRO, ASC, and BEAM were added individually to the STD program to create a total of four programs.

Data collection and analysis: Participants repeated Hearing in Noise Test sentences presented at 0 degrees azimuth with R-SPACE restaurant noise at two noise levels, 60 and 70 dB SPL. The reception threshold for sentences (RTS) was obtained for each processing condition and noise level.

Results: In 60 dB SPL noise, BEAM processing resulted in the best RTS, with a significant improvement over STD and ADRO processing. In 70 dB SPL noise, ASC and BEAM processing had significantly better mean RTSs compared to STD and ADRO processing. Comparison of noise levels showed that STD and BEAM processing resulted in significantly poorer RTSs in 70 dB SPL noise compared to the performance with these processing conditions in 60 dB SPL noise. Bilateral participants demonstrated a bilateral improvement compared to the better monaural condition for both noise levels and all processing conditions, except ASC in 60 dB SPL noise.

Conclusions: The results of this study suggest that the use of processing options that utilize noise reduction, like those available in ASC and BEAM, improve a CI recipient's ability to understand speech in noise in listening situations similar to those experienced in the real world. The choice of the best processing option is dependent on the noise level, with BEAM best at moderate noise levels and ASC best at loud noise levels for unilateral CI recipients. Therefore, multiple noise programs or a combination of processing options may be necessary to provide CI users with the best performance in a variety of listening situations.

Figure 1

A schematic diagram of the R-SPACE™ Array showing the eight loudspeakers in a 360 degree arc, 24 inches from the listener. Figure taken from Compton-Conley et al (2004) and used with permission from the author.

Figure 2

Mean soundfield thresholds (dB HL) and +/− 1 standard deviation for the CI with STD processing at user settings.

Figure 3

Mean RTS for unilateral participants in 60 dB SPL noise with STD, ADRO, ASC, and BEAM processing options. Error bars represent +1 standard deviation. The asterisks represent a significant difference between processing options (p≤0.05).

Figure 4

Mean RTS for unilateral participants in 70 dB SPL noise with STD, ADRO, ASC, and BEAM processing options. Error bars represent +1 standard deviation. The asterisks represent a significant difference between processing options (p≤0.05).

Figure 5

Mean RTS difference between noise levels (60 and 70 dB SPL) for unilateral participants (RTS at 70 dB SPL – RTS at 60 dB SPL) with STD, ADRO, ASC, and BEAM processing options. Error bars represent +1 standard deviation. The asterisks represent a significant difference between noise levels within processing options (p≤0.05).

Figure 6

Mean RTS of bilateral participants in 60 dB SPL noise with STD, ADRO, ASC, and BEAM processing options. Mean RTSs are shown for unilateral right ear, unilateral left ear, and bilateral conditions.

Figure 7

Mean RTS of bilateral participants in 70 dB SPL noise with STD, ADRO, ASC, and BEAM processing options. Mean RTSs are shown for unilateral right ear, unilateral left ear, and bilateral conditions.