For the moment, reading minds is a cumbersome process and there is no chance scientists could spy on decision-making surreptitiously. Haynes' studies focus on people who choose between just two alternatives, not the infinite number present in everyday life.
But scientists are making enough progress to make ethicists nervous, since the research has already progressed from identifying the regions of the brain where certain thoughts occur to identifying the very content of those thoughts.
"These technologies, for the first time, give us a real possibility of going straight to the source to see what somebody is thinking or feeling, without them having any ability to stop us," said Dr. Hank Greely, director of Stanford University's Center for Law and the Biosciences.
"The concept of keeping your thoughts private could be profoundly altered in the future," he said.
Civil libertarians are concerned that mind-reading technology may fit into a trend of pre-emptive security measures in which authorities could take action against individuals before they commit a crime — a scenario explored in the 2002 science fiction film "Minority Report."
Already, Britain is creating a national DNA database that would allow authorities to track people with violent predispositions. In addition, the government has also floated the idea of locking up people with personality disorders that could lead to criminal behavior.
"We need to start thinking about how far we are going to allow these technologies to be used," said Wolpe.
Despite the fears, Haynes believes his research has more benign practical applications.
For example, he says it will contribute to the development of machines already in existence that respond to brain signals and allow the paralyzed to change TV channels, surf the Internet, and operate small robotic devices.
For now, the practical applications of Haynes' research are years if not decades away.
"We are making the first steps in reading out what the specific contents of people's thoughts are by trying to understand the language of the brain," Haynes said. "But it's not like we are going to have a machine tomorrow."
