A study by MIT neuroscientists provides evidence that feedforward processing—the flow of information in only one direction, from retina through visual processing centers in the brain—is sufficient for the brain to identify concepts without having to do any further feedback processing. It also suggests that while the images are seen for only thirteen milliseconds before the next image appears, part of the brain continues to process those images for longer than that, senior author Mary Potter explained, because in some cases subjects weren’t asked whether a specified image was present until after they had seen the sequence. “If images were wiped out after 13 milliseconds, people would never be able to respond positively after the sequence. There has to be something in the brain that has maintained that information at least that long,” she says. This ability to identify images seen so briefly may help the brain as it decides where to focus the eyes, which dart from point to point in brief movements called fixations about three times per second. Deciding where to move the eyes can take 100 to 140 milliseconds, so very high-speed understanding must occur before that.