"Before we present the task, we can use brain activity to predict with about 70 percent accuracy whether the subject will give a correct or an incorrect response," says lead author Ayelet Sapir, Ph.D., a postdoctoral research associate in neurology. Eleven seconds before volunteers played the game -- discriminating the direction of a field of moving dots -- scientists showed them a hint: an arrow pointing to where the moving dots were likely to appear. The dots were visible only for one-fifth of a second and therefore were easy to miss if a subject was not paying attention to the right area.
After the hint and prior to the appearance of the moving dots, researchers scanned the volunteers with functional brain imaging, which reveals increases in blood flow to different brain areas indicative of increased activity in those regions. Based on brain activity patterns that reflected whether the subjects used the hint or not, scientists found they could frequently predict whether a volunteer's response would be right or wrong before the volunteers even had a chance to try to see the dots.
Results are published online in the Proceedings of the National Academy of the Sciences and will appear in the journal's print edition on Dec. 6.
Sapir and her colleagues concluded that volunteers don't use the hint the same way every trial. One speculation was that some of the brain signals they detected might be signs of the brain's struggle to cope with an ambiguity built into the test: the volunteers knew the hint was only accurate 80 percent of the time.
"Whether the hint is accurate or not was determined by the computer's random number generator, and the volunteers were not going to be able to beat that
Contact: Michael C. Purdy
Washington University School of Medicine