The Vanishing Ball
Illusion: A new perspective on the
perception of dynamic events
Gustav Kuhn
Ronald A Rensink
Cognition, 148:
64-70. [web]
Our perceptual experience
is largely based on prediction, and as such can be influenced by knowledge of
forthcoming events. This susceptibility is commonly exploited
by magicians. In the Vanishing Ball Illusion, for example, a magician
tosses a ball in the air a few times and then pretends to throw the ball again,
whilst secretly concealing it in his hand. Most people claim to see the ball
moving upwards and then vanishing, even though it did not leave the magician’s
hand (Kuhn & Land, 2006; Triplett, 1900). But what exactly can such
illusions tell us? We investigated here whether seeing a real action before the
pretend one was necessary for the Vanishing Ball Illusion. Participants either
saw a real action immediately before the fake one, or only a fake action.
Nearly one third of participants experienced the illusion with the fake action
alone, while seeing the real action beforehand enhanced this effect even
further. Our results therefore suggest that perceptual experience relies both
on long-term knowledge of what an action should look like, as well as exemplars
from the immediate past. In addition, whilst there was a forward displacement
of perceived location in perceptual experience, this was not found for oculomotor responses, consistent with the proposal that two
separate systems are involved in visual perception.