*2.1.4 Other brain signals*

Other techniques that are used to obtain EEG data include auditory evoked potential (a corresponding EEG pattern generated after an auditory stimulation), vibrotactile evoked potential (a corresponding EEG activity generated after physical vibrations at a particular frequency), imagined speech (imagination of words or sentences for evoking EEG signals), and error-related potential (an activity when a mismatch between the subject's intention and the output response from the BCI application is detected). One of the increasingly popular way to obtain EEG data is by analyzing EEG spectral changes to monitor users' drowsiness, attention, mental workload, emotions and other states of the mind [2]. This can become handy in detecting drivers' concentration at work, or in criminal cases when lie detector machine is employed.
