Scientists at the University of California at Berkeley have found a way to eavesdrop inside another person's mind.
In a small study that might sound like science fiction, the researchers could predict what people were hearing based on their brain activity.
"As you listen to a sound, it activates certain parts of the auditory cortex of your brain," said Brian Pasley, a UC Berkeley neuroscientist and lead author of the study published today in PLoS Biology. "We're interested in how the brain converts sound into meaning, so we looked at an early step in a long process."
To study the relationship between sound and brain activity, Pasley and his team enlisted the help of 15 epilepsy patients who had electrodes implanted in their brains. As the patients listened to a series of words, such as "structure," "doubt" and "property," the researchers recorded their brain activity. They then developed a computer model to match the sounds with the brain signals.
"You can think of the brain as a piano and the recordings as the keys," said Pasley. "You could turn off the sound and an expert pianist would still have a good idea of what note was being produced. We're trying to be the expert pianist."
When the researchers relied on the model to hear what the patients heard, they got an eerie version of the actual word -- a mash-up of all the sounds that matched the pattern of brain activity.
Pasley hopes to fine-tune the model to discern different types of words, like nouns and verbs, and even their meanings.
"This study mainly focused on lower-level acoustic characteristics of speech. But I think there's a lot more happening in these brain areas than acoustic analysis," he said. "We sort of take it for granted, the ability to understand speech. But your brain is doing amazing computations to accomplish this feat."
The study also opens the door for technology that could help paralyzed people communicate. If hearing a word and imagining a word activate similar brain areas, it might be possible to develop a "prosthetic device" for speech, Pasley said.
"We'd like to learn more about the imagery process -- how similar or different it is from when we're actually hearing sounds," he said. "If it's similar, this approach could have some clinical application down the line."
In September 2011, another UC Berkeley team used brain imaging to see YouTube videos through another person's eyes.
"If you can decode movies people saw, you might be able to decode things in the brain that are movie-like but have no real-world analog, like dreams," Jack Gallant, a professor of psychology at UC Berkeley and co-author of the study told ABC News in September.
Together, the studies point to the very real possibility of one day reading another person's thoughts.