If the mind controls the brain signal, how would a BCI user optimally control her mind, brain signal, and device? In my view the best path forward is to first gain a clear understanding of the mind. How can it be best understood, and defined?
For example, consider a “move the cursor” intention. Let’s say the cursor has 5 degrees of freedom: left, right, up, down, and stop. Potential mind/brain signatures would be a cursor’s size and shape, its movement (left, right…), and the perception of a computer screen. These are predominately signatures of visual perception. Goal or thought targets could be “attend to the cursor,” and “move the cursor left.” An emotional target state might be “calm and focused.” And so on.
The point is, any state of mind can be defined as a (general) memory set: “cursor visual characteristics & movement,” a “watch the cursor” goal, etc. The user would endeavor to strongly, selectively, and consistently hit these state of mind targets. These are some (of many possible) brain signal targets.
Brain signal noise would also mirror that of the mind. Noise would include emotions such as momentary success or failure, strong desire; the meaning of the task — i.e. why the user wants to move the cursor in a given context; environmental/social settings of lab, work, or home; and life context such as a job promotion, relocation, or loss of a loved one.
In short, any state of mind is most accurately defined as a set of general memories, which are (definable!) brain signal targets (to hit or avoid) for the user.