Why do we keep falling for this? If the rabbit wriggles in the supposedly empty hat or the pretty assistant in the box riddled with sabers, even sworn realists can no longer believe their eyes. Are you so easily fooled?
To dazzle their viewers, savvy illusionists often need nothing more than a few tools - and the ability to deftly manipulate the audience's attention. But stop! Before reading any further, first click on the video called Trick 1 in the "Media" column on the left and watch a little magic show.
Did you figure out how the trick works? It's actually quite simple: If the magician throws the ball up and makes it disappear for the third time, then obviously someone outside the camera frame has caught it.
If you're inclined towards that statement, at least you're in good company. After all, in an experiment conducted by Gustav Kuhn and Michael Land of the Universities of Durham and Sussex, 68 percent of the subjects reported seeing the ball rise and then not reappear. The explanation most often given was the hidden second man catching the ball.
In fact, the ball never left my hand on the third "throw". Through posture and line of sight, the magician makes his viewers believe exactly that. If the corresponding facial expressions and gestures were missing - as in a control experiment by the authors (video trick no. 2) - the illusion was gone. Such "social signals", as the authors call them, apparently play a greater role in perception than what we actually see. If there is also an unconscious expectation, the brain simply hides the contradictory information from the eyes.
Because of course almost all test subjects were convinced that they hadn't taken their eyes off the ball for a moment. Right? Yes and no, determined the scientists, who followed the eye movements of the test subjects with a special device. When the ball was still there, the subjects occasionally followed it with their eyes, looking primarily at the highest point of its trajectory. More often, however, they would stare at the magician's hands and face, apparently to infer the location of the ball.
What surprised the researchers most, however, was that none of the test subjects looked at the spot where they thought the ball had disappeared. Unlike its owner, the eye - more precisely, the system that controls the eye muscles - was not fooled by the magician's signals: when there was no longer a ball in view, it did not follow its imaginary trajectory, but stared steadfastly at the face of the magician magician.
Kuhn and Land see this as a confirmation of the thesis that optical impressions take two different routes, depending on whether they are used to control movement or for actual sensory perception. While the former relies solely on the information from the eye and interprets it step by step, conscious perception arises in the interplay of expectation, experience and what is seen.
Have fun and watch the video trick no. 1 a second time. Then you will notice how your new expectations have affected perception. You shouldn't be that easy to fool with this trick anymore!