An electroencephalogram (EEG) device records brain activity by attaching small sensors to the scalp to pick up the electrical signals produced by the brain. These signals are recorded by a machine and are looked at by a researcher for insights into user experience.
EEG devices have been used for various studies gauging emotional reactions to images, music, speeches, shows, and audio recordings.
Here is an image of a study participant using an EEG device.
A study participant wearing an EEG device.