Perceptual consequences of different signal changes due to binaural noise reduction: do hearing loss and working memory capacity play a role?
OBJECTIVES In a previous study, ) investigated whether pure-tone average (PTA) hearing loss and working memory capacity (WMC) modulate benefit from different binaural noise reduction (NR) settings. Results showed that listeners with smaller WMC preferred strong over moderate NR even at the expense of poorer speech recognition due to greater speech distortion (SD), whereas listeners with larger WMC did not. To enable a better understanding of these findings, the main aims of the present study were (1) to explore the perceptual consequences of changes to the signal mixture, target speech, and background noise caused by binaural NR, and (2) to determine whether response to these changes varies with WMC and PTA. DESIGN As in the previous study, four age-matched groups of elderly listeners (with N = 10 per group) characterized by either mild or moderate PTAs and either better or worse performance on a visual measure of WMC participated. Five processing conditions were tested, which were based on the previously used (binaural coherence-based) NR scheme designed to attenuate diffuse signal components at mid to high frequencies. The five conditions differed in terms of the type of processing that was applied (no NR, strong NR, or strong NR with restoration of the long-term stimulus spectrum) and in terms of whether the target speech and background noise were processed in the same manner or whether one signal was left unprocessed while the other signal was processed with the gains computed for the signal mixture. Comparison across these conditions allowed assessing the effects of changes in high-frequency audibility (HFA), SD, and noise attenuation and distortion (NAD). Outcome measures included a dual-task paradigm combining speech recognition with a visual reaction time (VRT) task as well as ratings of perceived effort and overall preference. All measurements were carried out using headphone simulations of a frontal target speaker in a busy cafeteria. RESULTS Relative to no NR, strong NR was found to impair speech recognition and VRT performance slightly and to improve perceived effort and overall preference markedly. Relative to strong NR, strong NR with restoration of the long-term stimulus spectrum and thus HFA did not affect speech recognition, restored VRT performance to that achievable with no NR, and increased perceived effort and reduced overall preference markedly. SD had negative effects on speech recognition and perceived effort, particularly when both speech and noise were processed with the gains computed for the signal mixture. NAD had positive effects on speech recognition, perceived effort, and overall preference, particularly when the target speech was left unprocessed. VRT performance was unaffected by SD and NAD. None of the datasets exhibited any clear signs that response to the different signal changes varies with PTA or WMC. CONCLUSIONS For the outcome measures and stimuli applied here, the present study provides little evidence that PTA or WMC affect response to changes in HFA, SD, and NAD caused by binaural NR. However, statistical power restrictions suggest further research is needed. This research should also investigate whether partial HFA restoration combined with some pre-processing that reduces co-modulation distortion results in a more favorable balance of the effects of binaural NR across outcome dimensions and whether NR strength has any influence on these results.