A processing system obtains a deformation signal generated by a deformation sensor. The deformation signal is indicative of a deformation of an outer ear of a user of a hearing instrument. Additionally, the processing system obtains an EMG signal generated by an electrode in a concha of the user, wherein the electrode is configured to detect activity of an intrinsic auricular muscle of the user. Furthermore, the processing system generates information regarding an auditory attention state of the user based on the deformation signal and the EMG signal. The processing system controls, based on the information regarding the auditory attention state of the user, the parameter of the audio system.