EEG measures mass synchrony between different areas of the brain. That's extremely hard to control consciously and takes a lot of practice. Even when you can

EEG measures mass synchrony between different areas of the brain. That's extremely hard to control consciously and takes a lot of practice. Even when you can do it, it's a 1-dimensional signal. It's not even clear you want to control it consciously; EEG therapy is used in psychiatry every now and then for treatment of a few disorders, and can lead to personality changes. The "inverse EEG" problem, which relates to the distortion caused by the skull, is basically computationally intractable (which is why ECoG is used). EEG is also totally drowned out by EMG (muscles) if you aren't careful, and it's nearly impossible to tell EMG and EOG (eye movements) apart from "real" EEG. In Emotiv's specific case, though, these fundamentals are the least of their problems. They're three (four?) years behind schedule without anything really shipping even now, and the units that I have seen in the wild are of low build quality.