British researchers have taken the first steps towards reading people's minds using straightforward brain-scanning techniques.
Scientists had a clearer idea of which images volunteers had seen after examining their brain recordings than the volunteers themselves, a paper published this week in the journal Nature Neuroscience reveals.
Geraint Rees and John-Dylan Haynes, both from University College London, used simple functional magnetic resonance imaging scans to record brain activity while volunteers viewed two different test objects.
A single two-second measurement of brain activity was enough for them to state with 80 per cent accuracy which of the two images a volunteer was seeing.
Dr Rees, who is based at UCL's Institute of Cognitive Neuroscience, said:
"If our approach could be expanded upon, it might be possible to predict what someone was thinking or seeing from their brain activity alone."
Strikingly, the study also showed that the brain could register images subliminally, even when the individual was not conscious of having seen them. When the researchers flashed up two images in fast succession, volunteers were conscious of seeing only the second one.
But the brain recordings could still predict both images.
Dr Rees said: "The next stage of our research is to explore whether brain activity can be used to predict how our stream of consciousness changes over time."
He added: "In principle, the technique could be applied to a device such as a lie detector, but more research would be needed."
Dr Rees explained that to develop such a device scientists would have to explore which areas of the brain could predict whether or not the subject was lying.
These areas might not produce signals as strong as the visual cortex - the part of the brain that processes information sent by the eyes.