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Single microphone noise reduction (NR) in hearing aids can provide a subjective benefit even when there is no objective improvement in speech intelligibility. A possible explanation lies in a reduction of listening effort. Previously, we showed that response times (a proxy for listening effort) to an auditory-only dual-task were reduced by NR in normal-hearing (NH) listeners. In this study, we investigate if the results from NH listeners extend to the hearing-impaired (HI), the target group for hearing aids. In addition, we assess the relevance of the outcome measure for studying and understanding listening effort. Twelve HI subjects were asked to sum two digits of a digit triplet in noise. We measured response times to this task, as well as subjective listening effort and speech intelligibility. Stimuli were presented at three signal-to-noise ratios (SNR; –5, 0, +5 dB) and in quiet. Stimuli were processed with ideal or nonideal NR, or unprocessed. The effect of NR on response times in HI listeners was significant only in conditions where speech intelligibility was also affected (–5 dB SNR). This is in contrast to the previous results with NH listeners. There was a significant effect of SNR on response times for HI listeners. The response time measure was reasonably correlated ( R142 = 0.54) to subjective listening effort and showed a sufficient test–retest reliability. This study thus presents an objective, valid, and reliable measure for evaluating an aspect of listening effort of HI listeners.

Objective: Previous studies on single microphone noise reduction (NR) in hearing aids (HAs) have shown that some NR algorithms provide beneficial effects in terms of listener preference. To improve HA user satisfaction, we are interested in characteristics that determine preferences for NR, and in the inter-individual variability. The aim of this study was to test if dynamic properties of NR influence listener preference. Design: The gain reduction at speech offsets of a NR algorithm was slowed down by applying temporal exponential smoothing. At speech onsets the gain recovery was left unchanged. Test signals consisted of speech in continuous and modulated speech-shaped background noise, processed with three time constants: 0, 100, and 200 ms. Study sample: 16 Normal hearing (NH) and 16 hearing impaired (HI) subjects participated in a paired-comparison listening test. Results: NH subjects as a group had a significant preference for NR with time constants of 100, or 200 ms (slower acting NR). HI listeners as a group preferred NR over no NR, but had no clear preference for fast or slow NR. Patterns of preference differed between individual listeners. Conclusions: NR dynamics had an impact on individual listener preference and should be considered when optimising HAs.

The mechanism of action of the holmium laser lithotripsy is attributed to explosive expanding and imploding vapor bubbles in association with high-speed water jets creating high mechanical stress and cracking the stone surface. A good understanding of this mechanism will contribute to the improvement and the safety of clinical treatments. A new method has been developed to visualize the dynamics of mechanical effects and fluid flow induced by Holmium laser pulses around the fiber tip and the stone surface. The fiber tip was positioned near the surface of a stone on a slab of polyacrylamide gel submerged in water. The effects were captured with high speed imaging at 2000-10000 f/s. The dynamics of the pressure wave after the pulse could be visualized by observing the optical deformation of a fine line pattern in the background of the water container using digital subtraction software. This imaging technique provides a good understanding of the mechanical effects contributing to the effectiveness and safety of lithotripsy and can be used to study the optimal fiber shape and position towards the stone surface.