The researchers say their work opens the door for brain-reading devices—like those envisioned by Philip K. Dick and other science-fiction writers—that display a person's inner visual experiences on a screen.
Before such a device can be built, however, researchers must first answer important questions about dreams, memories, and imagination.
(Related: "First Ever Brain 'Atlas' Completed [September 26, 2006].)
"Perhaps the contents of our imaginations are not represented in the same way as the contents of our actual real perceptions," Kay said.
"In this case, we will have to investigate how imagination is represented and construct appropriate computational models."
Technology will have to improve as well.
Many critics of fMRI point out that the technique does not measure brain activity directly. As a result, it lacks the resolution of data recorded directly from brain cells.
Frank Tong, a neuroscientist at Vanderbilt University in Tennessee, said he was surprised that the team's method worked as well as it did for this very reason.
"Most people think of fMRI as a pretty crude method, but [the data collected] contained a surprising amount of information, enough to predict, well above [the level of mere] chance, which of several hundred or thousand pictures a person was looking at," said Tong, who was not involved in the study.
The work also builds on other groundbreaking studies, including research reported last year in the journal Current Biology, in which researchers were able to decode the simple intentions of participants about 70 percent of the time based on fMRI readings.
Robert Dougherty, a neuroscientist at Stanford University, said the construction of a brain-reading device might be possible, but he cautions that the team's new model is only a small step toward that goal.
"Their model is not invertible—it cannot generate a unique image from the measured brain activity," Dougherty added.
"However, combined with strong assumptions about natural image statistics, a more sophisticated model could produce such images that would be a prediction of a subject's visual imagery."
A brain-reading device would be valuable for probing phenomena that are difficult to study using conventional means, such the differences in perception among people, the researchers said.
But the team notes that such a device could be used for more sinister purposes as well.
The privacy and ethical concerns associated with a brain-reading device would parallel those surrounding human genome sequencing, the researchers said.
In both cases, care will need to be taken so that the rights of individuals are not violated.
"The authors believe strongly that no one should be subjected to any form of brain-reading process involuntarily, covertly, or without complete informed consent," the team wrote in a statement.
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