Before they went to sleep, the participants were also trained on how to communicate their answers. Special sensors measured people’s eye movements or experts would judge their facial movements.

For example, a typical question would be to ask what is 8 minus 6. A 19-year-old American man was able to respond by moving his eyes left-right, left-right — two times — to signal “2.” Researchers asked the question again and he moved his eyes the same way two times again.

Out of the 158 trials among 36 participants, about 18% of the time they were able to give correct answers. In another 18%, it wasn’t clear if participants were responding or not. They were wrong 3% of the time. Most often, 61%, participants didn’t respond at all.

For the people dreaming, they didn’t always interpret the questions they were hearing as a simple question from researchers. “Sometimes stimuli were perceived as coming from outside the dream, but other times the stimuli emanated from elements of the dream, contextualized in a way that made sense in relation to ongoing dream content,” the researchers write. In one case, one participant “heard the questions transposed over their dream as though it was God talking to them,” Konkoly says.