gms | German Medical Science

Beamforming (spatial filtering) and (spectral) postfiltering algorithms are widely used noise reduction techniques in hearing aids to improve speech intelligibility, reduce listening effort, and increase comfort of listening. However, the actual benefit that a person achieves from commercially available noise reduction algorithms depends on many variables, such as the acoustic scenario, the effectiveness of processing, the severity of hearing impairment, and the acoustic coupling. This contribution investigates the relationship between individual closedness of the acoustic coupling and the speech intelligibility benefit from noise reduction settings using hearing aids, while controlling for other variables. Twenty-four experienced hearing aid users were bilaterally fitted with high-end hearing aids according to the NAL-NL2 fitting procedure, using different types of instant ear-tips. Verification of the fitting was done using real-ear measurements. The individual closedness of the acoustic coupling was determined via real-ear occluded insertion gains (REOIG) in both ears, i.e., the difference between real-ear unaided gain (open ear) and real-ear occluded gain (with acoustic coupling and hearing aid switched off). Speech reception thresholds (SRTs) were assessed aided with both mild and strong noise reduction settings in a spatial scenario with symmetrically placed interfering talkers using the German Hearing In Noise Test (HINT).The individual SRT-benefit from noise reduction was found to be between -1 and +7 dB with an average of +2.8 dB. The speech intelligibility index-weighted average REOIGs were between 0 dB (open fitting) and -10 dB (closed fitting). Average REOIGs from each individuals ear with more closed fitting were found to be highly correlated (r = -0.62, p < 0.002) with SRT-benefit, indicating a higher SRT-benefit from noise reduction for a more closed acoustic coupling. The type of instant ear-tip did not directly predict the SRT-benefit. These results indicate that the actual speech intelligibility benefit achieved through noise reduction depends strongly on the individual closedness of fitting. Furthermore, these results underline the importance of the individual acoustic coupling for fully exploiting the possible speech-in-noise benefit available in hearing aids. This study was funded by the William Demant Foundation.