The use of so-called "open fittings" instead of individual ear shells has become very popular in hearing aid fitting, in particular because open fittings avoid the occlusion effect, but also because they are more comfortable, easier to manufacture, and cosmetically preferred. On the other hand however, there are acoustical issues with open fittings, including the mixture of direct and amplified sound, a poor low-frequency performance, an increased risk of feedback and a supposedly less reproducible position of the sound delivering device (tubing or speaker) in the ear canal, which in turn may result in a greater variability of acoustic parameters such as RECD and REOG. The two latter issues are addressed here in a study with 20 subjects, for individual shell and a number of open fittings, comprising closed and open domes of different diameters with tubings as well as with ear canal receivers. It was observed that in comparison to individual shell fittings, the open fittings did not exhibit a higher variability of RECD and REOG, but up to 15dB (closed domes) to 25dB (open domes) lower feedback thresholds.

The findings from this study strongly suggest that measuring DTs and RTs with the stimulus set nLF is beneficial and useful to quantify the effects of HAs and NLFC on high-frequency speech cues for detection and recognition tasks. The findings also suggest that both tests are necessary because they assess audibility as well as recognition abilities, particularly as they relate to speech modification algorithms. The experiments conducted in this study did not allow for any acclimatization of the participants to increased high-frequency gain or NLFC. Further investigations should therefore examine the impact on DTs and RTs in the PPT as well as the contrasting effects of strong setting of NLFC to DTs and RTs because of (re)learning of modified auditory representations of /s/ and /ʃ/ as caused by NLFC.

This study investigated the influence of hearing-aid (HA) and cochlear-implant (CI) processing on consonant perception in normal-hearing (NH) listeners. Measured data were compared to predictions obtained with a speech perception model [Zaar and Dau (2017). J. Acoust. Soc. Am. 141, 1051-1064] that combines an auditory processing front end with a correlation-based template-matching back end. In terms of HA processing, effects of strong nonlinear frequency compression and impulse-noise suppression were measured in 10 NH listeners using consonant-vowel stimuli. Regarding CI processing, the consonant perception data from DiNino et al. [(2016). J. Acoust. Soc. Am. 140, 4404-4418] were considered, which were obtained with noise-vocoded vowel-consonant-vowel stimuli in 12 NH listeners. The inputs to the model were the same stimuli as were used in the corresponding experiments. The model predictions obtained for the two data sets showed a large agreement with the perceptual data both in terms of consonant recognition and confusions, demonstrating the model's sensitivity to supra-threshold effects of hearing-instrument signal processing on consonant perception. The results could be useful for the evaluation of hearing-instrument processing strategies, particularly when combined with simulations of individual hearing impairment.