# Evaluation of Two Self-Fitting User Interfaces for Bimodal CI-Recipients
###### Abstract
The different experiences and approaches of the experts has an impact on the hearing sensation with the two devices. One approach to overcoming these problems could be to let the users adjust the HA and CI settings themselves. In everyday situations, this could lead to an individual adjustment of the sound and to an improvement of the auditory sensation. This concept of self fitting was previously investigated for HAs by [PERSON] et al. [11] and for cochlea implants by [PERSON] et al. [6] and [PERSON] et al. [13]. They showed that self-fitting led to a higher acceptance of the sound in different environments but not to a higher speech intelligibility. However, bimodal users were not considered in these studies. In both studies, starting from an expert baseline setting, the user was allowed to amplify or attenuate certain frequency ranges of the input signal with the help of a tool. The user was thus able to adjust the sound to his or her personal preferences. Considering that the setting options for manipulating the input signal were the same for both devices, a bimodal solution should be feasible. Simultaneous fitting of the CI and the HA with the same self-fitting tool could also be used to compensate for the different fitting approaches used by the different experts during the initial fitting. Considering the fact that smartphones are becoming more and more popular throughout society, and even among the elderly population, they represent the perfect platform for such a self-fitting tool. In combination with the latest CI and HA generations with an integrated Bluetooth interface, the development of such self-care applications, generally called APPs, becomes possible. In existing apps in the HA field, the user interface (UI) mostly follows the basic principle of an equalizer. A good example of such an approach is the _myPhonak_ (Phonak) app, in which the low, mid, and high frequencies, as well as the overall volume, can be adjusted with the help of four sliders [14]. For CIs, there is a similar concept in the _Nucleus Smart_ APP, made by Cochlear. In this APP, the treble, bass, and overall volume can be adjusted [15]. However, other experimental approaches to a user interface can be found in the literature. One of these is the 2D-Surface UI that was used by [PERSON] et al. [16] and examined in more detail by [PERSON] et al. [11] and [PERSON] et al. [17]. With the help of this UI, the user can change the sound impression by moving a point with the fingertip on a touch-sensitive rectangular surface. Compared to other UIs, such a 2D-Surface can provide advantages. By minimizing the number of controls, the median duration of a self-fitting session could be reduced to less than one minute; at the same time, a high reproducibility was observed for such self-fitting under test-retest conditions. In comparison, participants required between 1 and 4 min for adaptation to other UIs tested [17]. We, therefore, decided to use the 2S-Surface approach in our study and compare it to the established equalizer based (EQ) approach. Thus, besides the goal of evaluating a self-fitting tool for bimodal users, another aim of this study was to compare the 2D-Surface UI to the EQ UI and to the current state-of-the-art expert fitting. We also wanted to examine whether the experience gained in the above-mentioned studies could be confirmed in the field of CIs, especially for bimodal users.