Reconstructing fine-grained cognition from brain activity.

We describe the Sketch-and-Stitch method for bringing together a cognitive model and EEG to reconstruct the cognition of a subject. The method was tested in the context of a video game where the actions are highly interdependent and variable: simply changing whether a key was pressed or not for a 30th of a second can lead to a very different outcome. The Sketch level identifies the critical events in the game and the Stitch level fills in the detailed actions between these events. The critical events tend to produce robust EEG signals and the cognitive model provides probabilities of various transitions between critical events and the distribution of intervals between these events. This information can be combined in a hidden semi-Markov model that identifies the most probable sequence of critical events and when they happened. The Stitch level selects detailed actions from an extensive library of model games to produce these critical events. The decision about which sequence of actions to select from the library is made on the basis of how well they would produce weaker aspects of the EEG signal. The resulting approach can produce quite compelling replays of actual games from the EEG of a subject.