Editing Brain–computer interface (section)

=====Bio/neurofeedback for passive BCI designs=====
Biofeedback can be used to monitor a subject's mental relaxation. In some cases, biofeedback does not match EEG, while parameters such as [[electromyography]] (EMG), [[galvanic skin response|galvanic skin resistance]] (GSR), and [[heart rate variability]] (HRV) can do so. Many biofeedback systems treat disorders such as [[Attention deficit hyperactivity disorder|attention deficit hyperactivity disorder (ADHD)]], sleep problems in children, teeth grinding, and chronic pain. EEG biofeedback systems typically monitor four brainwave bands (theta: 4–7&nbsp;Hz, alpha:8–12&nbsp;Hz, SMR: 12–15&nbsp;Hz, beta: 15–18&nbsp;Hz) and challenge the subject to control them. Passive BCI uses BCI to enrich human–machine interaction with information on the user's mental state, for example, simulations that detect when users intend to push brakes during emergency vehicle braking.<ref name=":0" /> Game developers using passive BCIs understand that through repetition of game levels the user's cognitive state adapts. During the first play of a given level, the player reacts differently than during subsequent plays: for example, the user is less surprised by an event that they expect.<ref name="ieeexplore.ieee.org"/>