Abstract: The proposed invention relates to a mobile device and methods for acquisition of biophysiological signals for the purpose of assessing mental states. The said mobile device is embedded into wireless headset that comprises headphones. The mobile device comprises sensors for biophysiological signal acquisition, including, but not limited to, electroencephalographic (EEG) signals, pulse oximetry, heart rate, body temperature and electrodermal activity. Furthermore, the device also measures environmental factors, including, but not limited to, ambient light and sound from the environment. The mobile device administers sound and visual stimuli to the user. The said biophysiological signals, after being processed, are used to assess mental states of the user (emotional states and cognitive processes). Furthermore, the intensity of the said mental states can be maintained at the same level, enhanced or weakened or fully modified using visual or sound stimuli.