Think once for “yes” and twice for “no”

BBC News yesterday ran a terrifying article about scientists successfully communicating with people who are apparently in persistent vegetative states.

The idea is straightforward enough.  The scientists told an apparently non-responsive man to imagine playing tennis if he wanted to indicate “yes,” and to imagine walking empty streets if he wanted to indicate “no.”  They then scanned his brain while asking him questions, and read his answers off of the different patters of activity.  Using this technique, he was able to answer