Magic Brain

Face test

"We have as if a little magical trick built into this test," explains Lavie, whose research on change blindness was highlighted in Discover Magazine. "There is some flicker between the first image and the second image. That flicker serves to disrupt the location of attention. And that is akin by analogy to the magic trick, to the disruption that the magician will use."

Normally, people do well on the test, easily spotting changes by simply paying careful attention. But Lavie had a trick up her sleeve. In earlier experiments, she had subjects take the test while an MRI machine scanned their brains. The results indicated that the parietal cortex had something to do with visual processing even though it's not part of the brain region traditionally thought to help code for visual awareness.

"People are surprisingly not able to [recognize the changes] if their attention is diverted, or if the activity in the parietal cortex is disrupted by using a TMS machine," Lavie says.

So, change blindness tricks the brain into temporarily tricking the eye. But she stresses that we needn't be visually distracted to experience change blindness: "You may think that in order to notice important changes, say in situations where you're driving, all you need is to put your eyes on the road. But our research tells us that this is not enough, that the brain simply doesn't work in this way… You have to have your attention and your parietal cortex on the road as well," she says. "So, in other words, it's not just your eye that has to be on it in order to perceive a change, but it's also your mind's eye."

That means change blindness is potentially as dangerous as it is enjoyable, resulting in visual mishaps in everyday life, like missing a changing traffic signal because you're talking and driving.