Biofeedback is the process of measuring an individual’s physiological states and feeding back that information to them in order to help them gain awareness and control over their physiological activity for the purpose of health improvement . Biofeedback has an extensive history in scientific literature and has already been shown to be efficacious as a treatment for a large variety of physical [2-4], as well as mental health issues including stress and anxiety [5-7]. However, it is still not widely implemented in standard treatment programs  and mechanisms through which biofeedback works remain largely unexplored. To address these gaps, the current project is aimed at assessing the potential of novel, interactive biofeedback interventions as well as identifying important factors that could contribute to its efficacy.
Current studies focus on assessing the potential of DEEP, a biofeedback-based virtual reality (VR) game. In this game, players move through an enchanting underwater world by using their own breath. The game is developed by Owen Harris and Niki Smit (Monobanda PLAY) to provide players with a sanctuary where they can de-stress. Within this project, the game is currently being further developed and validated as a possible intervention for children with anxiety. DEEP stimulates players (through biofeedback) to use deep, diaphragmatic breathing. It is played by using a VR headset combined with a customized belt that measures the expansion of the diaphragm. The values of this sensor influence the game and are reflected in feedback in various ways. First of all, the player is informed about their breathing by way of their movement. Breathing in deeply gives the players an upward (when close to the ground) or forward force, and these forces are strengthened by deeply breathing out. The player is also given various forms of visual feedback. For example, a circle in the center of the screen shrinks and expands in accordance to the expansion of the player's diaphragm. In addition, elements in the environment (such as plants) change color or change in size/movement, mirroring the player's breathing. By giving this (bio)feedback to the player, they can become more aware of their breathing and are stimulated to breath in a deep and calm manner.
We believe that biofeedback games like DEEP have a lot of potential to be used as a tool for youth with anxiety. One core aspect of anxiety in youth is heightened physiological reactivity to stress and fear signals in the environment, influencing for instance heart rate and breathing. [8-9]. The core mechanism of DEEP, specifically the stimulation of deep, calm, diaphragmatic breathing, nicely reflects common techniques that are used to regulate stress [10-11] and that are used in current evidence-based anxiety treatments [8-9, 12-13]. In addition to the focus on breathing, games like DEEP offer, in comparison to conventional treatments, a fun and interactive way of learning, which can increase children’s motivation, thereby possibly increasing adherence. The virtual reality environment and biofeedback also helps to fully embody newly learned skills. A first pilot study has already shown promising results in children (N=86) between the ages of 8-12 . However, more research is needed to assess the potential of DEEP (and biofeedback games in general). Within this project, DEEP will be further developed by implementing and rigorously testing evidence-based techniques in future prototypes such as (visual) feedback, modeling  and exposure .