U.S. researchers reported Wednesday they had found the "mind's eye" by mapping the part of the brain used when people think about images.
Stephen Kosslyn and colleagues at Harvard University used positron emission tomography (PET) scans to watch the brain at work as 12 volunteers thought about various pictures.They found that the primary visual cortex, at the back of the brain, works when people imagine pictures just as when they actually look at something.
"The primary visual cortex is activated when subjects close their eyes and visualise objects," Koss-lyn and colleagues wrote in the science journal Nature.
The scientists asked their volunteers, all men, to memorize pictures of ordinary objects ap-pearing on a computer screen.
Their response was compared with other men who were blindfolded and asked to let their minds go blank or only given auditory cues.
Thinking about small images activated areas at the back of the visual cortex, while large images trig-gered regions at the front. Medium-sized images activated intermediate regions.
"These findings resolve a debate in the literature about whether imagery activates early visual cortex and indicate that visual mental imagery involves `depictive' representations, not solely language-like descriptions," they wrote.
"Moreover, the fact that stored visual information can affect processing in even the earliest visual areas suggest that knowledge can fundamentally bias what one sees."
The researchers did not test women. Other tests have shown that men and women process language in different parts of the brain.