In Star Wars, Obi-Wan Kenobi was on the right track in his advice to the young Luke Skywalker. People are fooled by magic tricks, even if their eyes see past the illusion, a new study reveals.

The tricks work by distorting our perception, even though they do not fool our eyes, the research shows. The study demonstrates that the brain pathways for eye movement and perception operate independently, the researchers say.

Gustav Kuhn at the University of Durham, UK, who is a neuroscientist and also a magician, showed 38 students a video clip of the “vanishing ball” illusion. Watch a brief clip of the trick (wmv format).

In the trick, the magician throws a ball into the air twice and catches it. On the third, fake throw, the ball seems to disappear into the air even though it never leaves his hand. Most of the students watching the trick were fooled by the magician looking up on the third throw – 68% perceived the ball as leaving his hand.

Eyes wide shut

To understand how volunteers were fooled, Kuhn and colleagues filmed their eyes as they watched the trick and used special software to calculate where they had looked. Most people glanced quickly at the magician’s face before tracking the ball, the researchers found.

The magician’s gaze influenced their perception of the ball’s location and this overruled the visual information coming from their eyes.

Kuhn then showed them a second video of the same trick, but this time the magician did not look up on the third throw. Less than one-third of the students were fooled by the illusion this time.

Interestingly, even volunteers who claimed to see the ball go up did not look at the area where they claimed to have seen the ball – regardless of where the magician gazed. Their eyes fixated lower, nearer to his hand. In fact, there was no difference between the eye movements of those who were fooled by the illusion and those who were not.

Little and large

The findings illustrate that the brain pathway governing perception operates independently from the pathway controlling eye movement, Kuhn says.

Previous research has also suggested that separate pathways exist for perception and action. For example, one well-studied patient, identified as D F, had brain damage that made it impossible for her to recognise objects, but she could still interact with them. In one test, she could not tell a large block apart from a small one – yet she would open her hand wider when reaching out to pick up the former.

It remains unclear why some people are more easily fooled by the "vanishing ball" than others. Perhaps, as Obi-Wan might have put it: "These aren't the balls you're looking for…"

Journal reference: Current Biology (DOI: 10.1016/j.cub.2006.10.012)