"We found that imagery leads to a short-term memory trace that can bias future perception," said Joel Pearson, lead author of the study and research associate at the Vanderbilt Department of Psychology.

"This is the first research to definitively show that imagining something changes vision both while you are imagining it and later on."

"These findings are important because they suggest a potential mechanism by which top-down expectations or recollections of previous experiences might shape perception itself."

The findings of the study show that the process can happen instantaneously.

"You might think you need to imagine something 10 times or 100 times before it has an impact," said Frank Tong, co-author of the study and associate professor of psychology.

"Our results show that even a single instance of imagery can tilt how you see the world one way or another, dramatically, if the conditions are right."

Previous research into vision has been stymied by the subjective nature of how we perceive imagery.

"It has been very hard to pin down in the laboratory what exactly someone is experiencing when it comes to imagery, because it is so subjective," said Tong.

"We found that the imagery effect, while found in all of our subjects, could differ a lot in strength across subjects."

"So this might give us a metric to measure the strength of mental imagery in individuals and how that imagery may influence perception."

The study may help to settle a long-standing debate in the field -- is vision a literal representation of what is there or is it something more abstract?

"More recently, with advances in human brain imaging, we now know that when you imagine something parts of the visual brain do light up and you see activity there," said Pearson.

"So there's more and more evidence suggesting that there is a huge overlap between mental imagery and seeing the same thing."

"Our work shows that not only are imagery and vision related, but imagery directly influences what we see."