The researchers played a sound before puffing air into the eyes of these patients. In some patients, there was a twitch in eye muscles as they anticipated the puff of air after the sound was played.
"These were classic Pavlovian experiments and some patients, but not all of them, started to respond," said study leader Dr Tristan Bekinschtein from the University of Cambridge. "They were clearly anticipating the stimulus would come, so there is some kind of perception and from the point of view of the patient who is allegedly unconscious this could have profound implications."
The details of the study appear in the latest issue of Nature Neuroscience.