The number of images recorded by security cameras each day vastly exceeds human analysts' ability to examine them. "Computer vision" systems aren't much help: they're still far too primitive to tell a prowler from a postman. But researchers say the human brain can subconsciously register an anomaly in a scene -- say, a shadow where there shouldn't be one -- much faster than a person can visually and verbally identify it. If computers could somehow monitor the brain and flag these "aha" moments, surveillance analysts might be able to scan many times more images per hour.

That's what Paul Sajda, a bioengineer at Columbia University's Laboratory for Intelligent Imaging and Neural Computing, hopes to enable with his "cortically coupled computer vision" system, or "C3Vision." Sajda's prototype, built with a grant from the U.S. Defense Advanced Research Projects Agency, includes a bonnet of electrodes that is placed on a subject's head, where it monitors changes in the brain's electrical activity. A computer scrutinizes those changes for the neural signatures of interesting events and images, as the subject watches a video running at 10 times its normal speed. The flagged images are picked out for a more intensive examination.