The year after his study with Tatler, Kuhn and neurobiologist Michael F. Land of the University of Sussex in England discovered that the spectators’ gaze did not point to where they themselves claimed to have seen the ball vanish. The finding suggested the illusion did not fool the brain systems responsible for the spectators’ eye motions. Instead, Kuhn and Land concluded, the magician’s head and eye movements were critical to the illusion, because they covertly redirected the spectators’ attentional focus (rather than their gaze) to the predicted position of the ball. The neurons that responded to the implied motion of the ball suggested by the magician’s head and eye movements are found in the same visual areas of the brain as neurons that are sensitive to real motion. If implied and real motion activate similar neural circuits, perhaps it is no wonder that the illusion seems so realistic.

Kuhn and Land hypothesized that the vanishing ball may be an example of “representational momentum.” The final position of a moving object that disappears is perceived to be farther along its path than its actual final position—as if the predicted position was extrapolated from the motion that had just gone before.

   
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