Towards more realistic hearing aid evaluation - influence of head movement
Creators: name: Hendrikse, Maartje M. E.
Publisher: name: Zenodo
Year: 2019
Subjects: hearing aid evaluation
head movement
virtual audiovisual environments
acoustic simulations
misalignment
maladaptation

description: Hearing aids have been around for many years. In addition to providing amplification of the sound environment, they aim to attenuate noise in order to increase the intelligibility of a target source. Beamformers are an example of hearing aid algorithms that aim to increase the signal-to-noise ratio (SNR). Since hearing aids are usually worn behind the ears, the direction of fixed beamformers is dependent on the head direction, and their performance could be affected by it. Thus, head movement is one of the factors that could explain the difference between the hearing aid algorithm benefit predicted in standard laboratory tests and the benefit in everyday life. Other factors are the lack of visual cues, which can influence the head movement behavior, and the low acoustic complexity of standard laboratory tests. In order to better predict the benefit in everyday life, test methods need to be developed that can assess communication in realistic conditions under natural head movement behavior in the laboratory. This thesis presents work towards the development of such methods. First it was investigated which visual cues need to be presented in order to measure head movement behavior that is comparable to real life. This is done in Chapter 2. Animated environments are preferred over video recordings to present visual cues, because they allow more freedom when designing the environments and there are no privacy issues. However, the validity and effect of different behavioral features of animated characters on the movement behavior needed to be checked. Therefore, Chapter 2 compares the participants’ movement behavior when no visual cues were presented, when video recordings of real persons were presented and when animated characters were presented. Animated characters with different behavioral features for lip movement and gaze movement were tested. Results showed that movement behavior, task performance, and perception were all influenced by visual cues, and that animated characters with certain behavioral features can be used to measure head movement in a valid way. In Chapter 3 animated characters with these behavioral features were used to design virtual audiovisual environments (VEs) that replicate relevant everyday listening situations in the laboratory. The VEs that were realized are listening situations in a living room, lecture hall, cafeteria, train station and street. These VEs were validated in terms of subjective experience and reproducibility of the movement behavior. Differences in movement behavior between the VEs were found and typical movement behavior was described in each VE. No behavioral groups could be identified, but age-related differences in movement behavior were found. In Chapter 4 acoustic simulations were done with the measured head movement and acoustic VEs from Chapter 3, to investigate the hearing aid algorithm performance related to noise suppression during realistic head movement. Performance can be affected when adaptive algorithms have to adjust to changes in the acoustic scene caused by head movement, the so-called maladaptation effect, or when directional algorithms are not facing in the optimal direction because of head movement, the so-called misalignment effect. Differences in performance for the different movement traces were found and related to effects of maladaptation and misalignment. Misalignment problems were found to severely affect the performance of directional algorithms. Furthermore, the maladaptation effect was investigated separately by looking at the SNR improvement of hearing aid algorithms after simulated rotational head movement in simple anechoic noise scenarios. Although an effect of maladaptation was found in these simple anechoic scenarios, no relevant effect could be found in the more realistic acoustic VEs from Chapter 3. This proves that the methodology developed in this thesis is capable of assessing acoustic communication under realistic conditions and head movement behavior, and thus may serve as a basis for the development of novel evaluation methods for hearing aids that are better able to predict the benefit in everyday life. It was shown that there is a need for improvement of directional algorithms and the tools provided here can help with the development and evaluation of new and better algorithms. This thesis could therefore help to increase the benefit of hearing aids in everyday life.