Experimental: Virtual Reality based therapy added real-time EEG-based neurofeedback (VR-NF)

Participants in the experimental group undergo 8 sessions of a manualized virtual reality-based intervention added real-time EEG neurofeedback aiming to enhance the control and sense of power in relation to the dominant hallucinated voice. Together with the therapist, the participants create a digital representation (avatar) in virtual reality corresponding to the visual perception and sound of the voice. During therapy, the participants will be encouraged to engage in a dialogue with the avatar. While immersed in virtual reality, EEG recordings will be conducted by electrodes connected to a cap on the participants' head. Processed EEG-data will provide real-time information on the participants' brain activity associated with the emotional distress when confronted with the avatar and will be visible both to the participant and therapist. The feedback will be used to continuously adjust the intervention to the brain activity and aims to help the participant practice emotion regulation.

Active_comparator: Virtual Reality - based therapy

Participants in the control group will be offered 8 sessions of a manualized virtual reality - based therapy that follows the same principles as described in the experimental arm. Together with the therapist, the participants create a digital representation (avatar) in virtual reality that corresponds to their visual perception of and sounds like their hallucinated voice. Thoughout the therapy sessions, the participants will be encouraged to engage in a dialogue with the 'avatar', voiced by the therapist who will alternate between talking as the 'avatar' and as a supportive therapist. The therapy aims at enhancing the participants' control and feeling of power in relation to the dominant hallucinated voice. Furthermore, the therapy focuses on regulating the emotional distress associated with the hallucinated voice.