The participants were a mile apart on campus. They could neither see nor speak to each other. But one knew that the other was thinking about tiramisu.
University of Washington researchers Andrea Stocco and Chantel Prat designed a brain-to-brain interface that lets two people communicate wordlessly and remotely over the Internet. The results of their groundbreaking "mental 20 Questions" study were published Wednesday in PLOS One.
"Evolution has spent a colossal amount of time to find ways for us and other animals to take information out of our brains and communicate it to other animals in the forms of behavior, speech and so on," Stocco, an assistant professor of psychology, said in a statement.
"But it requires a translation. We can only communicate part of whatever our brain processes. What we are doing is kind of reversing the process a step at a time by opening up this box and taking signals from the brain and with minimal translation, putting them back in another person's brain."
In this case, he and Prat essentially translated thoughts into flashes of light.
They separated pairs of participants into two darkened rooms almost a mile apart from each other. One participant, the "respondent," donned an electrode cap connected to an electroencephalography (EEG) machine that records electrical brain activity.
The other, the "inquirer," sat in front of a magnetic coil capable of stimulating his visual cortex to cause him to see a flash of light known as a phosphene, which can look like a blob, a wave or a thin line.
The respondent was presented an object on a screen to focus on, while the inquirer was presented with a list of possible objects (including the one in play) and a list of "yes" or "no" questions, such as, "Is it a liquid?" or "Is it sweet?" The inquirer could click on a question to send it to the respondent's screen.
To answer, the respondent looked at either the word "yes" or "no" on his screen. Each was associated with a light flashing at a different frequency. The EEG reading associated with either answer would send a signal to the coil behind the inquirer's head. But only an answer in the affirmative generated a response large enough to cause the inquirer to see a phosphene.
Therefore, the respondent knew: Flash of light equals "yes," no flash equals "no."
Given three rounds of question and answer over 20 games, ten participants were able to guess the correct object 72 percent of the time, compared with just 18 percent in control rounds.
The researchers said that wrong answers could have been caused by a number of factors including the respondents not knowing the right answer or focusing on both replies, or because the inquirer struggled to recognize a phosphene.
"They have to interpret something they're seeing with their brains," said Prat, a faculty member at the Institute for Learning & Brain Sciences and a UW associate professor of psychology. "It's not something they've ever seen before."
She added, "While the flashing lights are signals that we're putting into the brain, those parts of the brain are doing a million other things at any given time, too."
In 2013, the team successfully showed that one person's mind could remotely control another person's hand movements.
They are now exploring the possibility of "brain tutoring" -- transferring signals from healthy brains to ones that are developmentally impaired or impacted by external factors such as a stroke or accident, or sending knowledge directly from teacher to pupil.