When we conjure up a mental image – where we left the car keys or the aisle at the grocery store that might contain canola oil – we’re using the mind’s robust capacity to envision the outside world. But how do we know that the image conjured up is an authentic representation of reality?

A team of researchers asked the same question, and came up with a clever method to answer it. They asked participants to imagine a specific image in their heads: a red circle with horizontal lines or a green circle with vertical lines. They then used what’s known as a binocular rivalry test to see how the imagined image would affect people’s behavior later.

'If we stop for a moment and think about it, our ability to imagine the world around us in the absence of stimulation from that world is…amazing.'

In a binocular rivalry test, each eye is exposed to a different image, which confuses the brain: since the brain can’t actually process the two images in tandem, one of the images is typically remembered as dominant. One of the images included in the binocular rivalry test was the one previously imagined by the participants.

As the researchers suspected, the pattern that was initially imagined was the one that was later remembered (became dominant) during the binocular rivalry test. This finding led the researchers to suggest that what we imagine has very real and measurable effects on our behavior later. The team used a variety of control conditions to verify that other variables, like personal preference, did not explain the results.

Study author Joel Pearson says that "our ability to consciously experience the world around us has been dubbed one of the most amazing yet enigmatic processes under scientific investigation today." On the other hand, he says, "if we stop for a moment and think about it, our ability to imagine the world around us in the absence of stimulation from that world is perhaps even more amazing."

The results of the study have implications not only about how we imagine the world in the present, but also about how we conceive of events in the future. Pearson says imagining situations and scenarios is "one of the fundamental abilities that allows us to successfully think about and plan future events." Doing so "allows us to, in a sense, run through a dress rehearsal in our mind’s eye."

Future research will look into how the capacity to imagine can go awry, and lead to unwanted and problematic mental images such as hallucinations.

Pearson is affiliated with the University of New South Wales. The study will be published in the July 2011 issue of Psychological Science.