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Michael Natter, Flip Phillips; The french drop sleight: Deceptive biological motion. Journal of Vision 2008;8(6):1052. doi: 10.1167/8.6.1052.
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Purpose: To demonstrate the salience of an effect of the French drop sleight of hand illusion between expert, intermediate, and novice magicians. In addition, the extended purpose is to isolate the differences in motion between the three skill levels of the magicians and their contribution to the deception. Methods: Participants were asked to judge which hand of the coin was in after viewing a clip of one of three magicians (novice, intermediate, expert) in one of two conditions: either the magician taking the coin (true motion) or the magician giving the illusion of taking coin but actually keeping it in the same hand (deceptive motion). The performers were then outfitted with pressure sensors on the gripping fingers and the modulation of pressure was noted between both the true and deceptive conditions and across all three skill levels. Similarly, the magicians' trajectory of motion was observed using motion sensors equally placed along the arm, wrist, hand, and fingers of the three magicians in both conditions. Results: An effect was found between the three magicians (novice, intermediate, expert) with the participants responding less than chance when viewing expert, around chance when viewing intermediate, and better than chance when viewing the novice. It was also found that the change in pressure as the well as the trajectory differed across the three magicians. Conclusion: The greater majority of past literature in this field deals with the overt social cues of biological illusion yet this study highlights the distinct, biomechanical mechanism of such deceptive movement, suggesting that change in apparent pressure and trajectory are the key elements in this type of illusionary motion.
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