When talking about EEG-based "mind reading", there are three primary methods currently under study (when looking at locked-in patients at least):
1) P300 - This refers to a predictable change in the EEG signal that happens around 300 milliseconds after something you were expecting happens. For example, if I am looking for a particular letter to flash amongst a grid of letters all randomly flashing, a P300 will be triggered when the letter I want flashes.
2) SSVEP - This stands for steady state visually evoked potential. This approach uses EEG signals recorded from over the visual cortex, which responds to constantly flickering stimuli. Given a few seconds, the power of the frequency of the attended stimulus increases in the EEG, which can then be detected and used to make a decision.
3) SMR - This stands for sensorimotor rhythms, and is an approach that looks for changes in EEG activity over the motor cortex. Successful approaches have been able to identify when you imagine clenching your left or right fists, or pushing down on your foot. Unlike the other two, this does not require external stimuli.
SMR is the most like what we consider mind reading, as the user is initiating the signal while the other two infer what a person is looking at. It is limited to only 2-3 degrees of freedom at the moment, however, and is the hardest signal to work with. It is susceptible to external factors such as the current environment and mental state, and not everyone seems to be able to generate the needed signals. SSVEP, while lacking the wow factor of SMR, is much easier to work with and is a much more stable signal.
1) P300 - This refers to a predictable change in the EEG signal that happens around 300 milliseconds after something you were expecting happens. For example, if I am looking for a particular letter to flash amongst a grid of letters all randomly flashing, a P300 will be triggered when the letter I want flashes.
2) SSVEP - This stands for steady state visually evoked potential. This approach uses EEG signals recorded from over the visual cortex, which responds to constantly flickering stimuli. Given a few seconds, the power of the frequency of the attended stimulus increases in the EEG, which can then be detected and used to make a decision.
3) SMR - This stands for sensorimotor rhythms, and is an approach that looks for changes in EEG activity over the motor cortex. Successful approaches have been able to identify when you imagine clenching your left or right fists, or pushing down on your foot. Unlike the other two, this does not require external stimuli.
SMR is the most like what we consider mind reading, as the user is initiating the signal while the other two infer what a person is looking at. It is limited to only 2-3 degrees of freedom at the moment, however, and is the hardest signal to work with. It is susceptible to external factors such as the current environment and mental state, and not everyone seems to be able to generate the needed signals. SSVEP, while lacking the wow factor of SMR, is much easier to work with and is a much more stable signal.
Disclosure: I work in this area. Here's a flashy NSF video highlighting our lab: http://www.nsf.gov/news/special_reports/science_nation/brain...