# Evaluation of Two Self-Fitting User Interfaces for Bimodal CI-Recipients
###### Abstract  
Smartphones are increasingly being used to enable patients to play an active role in managing their own health through applications, also called apps. The latest generation of sound processors for cochlear implants offer Bluetooth connectivity that makes it possible to connect smartphones or tablets and thus enable patients to modify their hearing sensation or measure system parameters. However, to achieve a high adoption rate and secure operation of these applications, it is necessary to design intuitive user interfaces (UI) for end users. The main goal of the current study was to evaluate the usability of two different UIs. A second goal was to compare the hearing outcomes based on the patient's adjustments. The two different UIs were explored in a group of adult and older adult bimodal cochlear-implant users, with adjustments possible for both the cochlear implant and the contralateral hearing aid. One of the UIs comprised a classical equalizer and volume-dial approach, while the second UI followed a 2D-Surface concept, to manipulate the corresponding sound parameters. The participants changed their fitting parameters using both UIs in seven different sound scenes. The self-adjusted settings for the different scenarios were stored and recalled at a later stage for direct comparison. To enable an assessment of reliability and reproducibility, the self-adaptation was also repeated for two of the seven sound scenes. Within minutes, the participants became accustomed to the concept of both UIs and generated their own parameter settings. Both UIs resulted in settings that could be considered similar in terms of spontaneous acceptance and sound quality. Furthermore, both UIs showed high reliability in the test-retest procedure. The time required for adjustment was significantly shorter with the 2D-Surface UI. A closer look at the bimodal aspect shows that participants were able to compensate for differences in loudness and frequencies between the cochlear implant and the hearing aid. The blind comparison test showed that self-adjustment led to a higher acceptance of the sound perception in more than 80% of the cases. c 2023 13 8411. 12.12.  
normalization or loudness equalization principles. Both strategies take into account various patient and device characteristics. For example, the desired sensation level (DSL) method takes into account the patient's hearing thresholds, previous amplification experience, number of hearing aid channels, and volume exposure [2]. With current CI systems, it is possible to achieve good speech perception in a quiet environment [3; 4; 5]. However, in challenging environments, such as with background noise or reverberation, most users still have problems in understanding speech [6; 7; 8]. However, compared to a CI used alone, bimodal stimulation, i.e., combining electric (CI) and acoustic (HA) stimulation, can already lead to improvements in speech understanding in noise, in sound localization, and in music perception [9; 10]. Another important factor impacting speech perception is adequate fitting of the sound processors. Correctly assessing the thresholds and the upper stimulation levels are the most relevant settings in the adjustment process [6]. Generally, the fitting process of a HA or a CI is highly individual. The initial fit is usually made by an expert, i.e., an audiologist. The subsequent fine tuning is based on the expert's experience, taking into account the user's feedback. The fine-tuned HA or CI is then worn by the user under different listening conditions in everyday life. Further appointments for fine-tuning generally follow, until a setting is found that is satisfactory for the user [11; 12]. Such a fitting process may therefore take several sessions, and the final setting is very dependent on the experience of the expert and the time spent with the participant. It is precisely this point that often leads to problems, particularly for bimodal users, since the CI and HA may not be fitted by the same expert.