Potential Consequences of Spectral and Binaural Loudness Summation for Bilateral Hearing Aid Fitting.

Aversiveness of loud sounds is a frequent complaint by hearing aid users, especially when fitted bilaterally. This study investigates whether loudness summation can be held responsible for this finding. Two aspects of loudness summation should be taken into account: spectral loudness summation for broadband signals and binaural loudness summation for signals that are presented binaurally. In this study, the effect of different symmetrical hearing losses was studied. Measurements were obtained with the widely used technique of Adaptive Categorical Loudness Scaling. For large bandwidths, spectral loudness summation for hearing-impaired listeners was found to be greater than that for normal-hearing listeners, both for monaurally and binaurally presented signals. For binaural loudness summation, the effect of hearing loss was not significant. In all cases, individual differences were substantial.

Adjustments of the amplitude mapping function: Sensitivity of cochlear implant users and effects on subjective preference and speech recognition.

OBJECTIVE: In sound processors of cochlear implant (CI) users, input sound signals are analysed in multiple frequency channels. The amplitude mapping function (AMF) is the output compression function dictating the conversion from (acoustical) channel output levels to (electrical) current levels used for electrode stimulation. This study focused on the detectability of AMF adjustments by CI users and the effects of detectable AMF adjustments on subjective preference and performance. DESIGN: Just noticeable differences (JNDs) for AMF settings were measured for pre-processed sentences at 60 dB SPL in quiet and noise. Three AMF settings, ranging twice the JND, were used during a take-home trial period of 12 days. Subjective ratings were collected and speech recognition in quiet and noise was measured. STUDY SAMPLE: JND measurements: 17 CI users. Field experiment: 15 CI users. RESULTS: JNDs for AMF settings varied among subjects and were similar in quiet and noise. A steeper AMF in the lower part was advantageous for speech recognition in quiet at soft levels. Subjective ratings showed limited agreement with speech recognition, both in quiet and noise. CONCLUSIONS: CI users may benefit from different AMF settings in different listening situations regarding subjective preference and speech perception, especially for speech in quiet.

Interactive fitting of multiple algorithms implemented in the same digital hearing aid.

The main purpose of this study is to examine the applicability of an adaptive and interactive optimization strategy to fine-tune three hearing-aid algorithms simultaneously: dynamic compression, temporal signal enhancement, and noise reduction. The optimal combination of these three algorithms was determined by a multidirectional pattern search with an adaptive step size. Additionally, we applied a round-robin procedure to validate the results of the optimization procedure. For both procedures the listeners were asked to compare two consecutive, differently processed sentences in continuous and fluctuating background noises on speech intelligibility. Ten hearing-impaired and four normal-hearing subjects participated. The reliability and consistency of the multidirectional pattern search was low, especially for the fluctuating noise condition. The results of the round-robin procedure did not correspond closely with the pattern search results. These findings suggest that the current implementation of a multidirectional optimization procedure has not yet proven to be applicable for the necessary individual fine tuning of complex signal processing strategies, when the objective is to maximize speech intelligibility.