MSGID: 1:317/3 642cf974   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Sleight-of-hand magic trick only fools monkeys with opposable thumbs   
      
      
     Date:   
         April 4, 2023   
     Source:   
         University of Cambridge   
     Summary:   
         An illusion involving a hidden thumb confounds capuchin and squirrel   
         monkeys for the same reason it does humans -- it misdirects expected   
         outcomes of actions they can carry out. However, marmosets have   
         five equidistant digits, and were rarely fooled by the magician. The   
         research adds to evidence that animals struggle to predict movements   
         outside of their own 'biomechanical ability'.   
      
      
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   FULL STORY   
   ==========================================================================   
   By performing a famous magic trick for three species of monkey with   
   differing hand structures, scientists have discovered that -- in order   
   to deceive -- a conjuror needs a similar anatomy to their audience.   
      
      
   ==========================================================================   
   Psychologists used a sleight-of-hand trick called the French drop, in   
   which an object appears to vanish when a spectator assumes it is taken   
   from one hand by the hidden thumb of the other hand.   
      
   The study, carried out at the University of Cambridge's Comparative   
   Cognition Lab, found that monkeys lacking opposable thumbs did not fall   
   for the assumption -- staying wise to the whereabouts of tasty treats   
   a magician tried to make disappear.   
      
   The research suggest that sharing a biomechanical ability may be necessary   
   for accurately anticipating the movements of those same limbs in other   
   individuals.   
      
   This is true even when those apparently accurate predictions end in   
   befuddlement at the hands of an illusionist. The study is published   
   today in the journal Current Biology.   
      
   "Magicians use intricate techniques to mislead the observer into   
   experiencing the impossible. It is a great way to study blind spots   
   in attention and perception," said Dr Elias Garcia-Pelegrin, who has   
   practiced magic for a decade, and conducted the experimental work during   
   his PhD at Cambridge.   
      
   "By investigating how species of primates experience magic, we can   
   understand more about the evolutionary roots of cognitive shortcomings   
   that leave us exposed to the cunning of magicians."  "In this case,   
   whether having the manual capability to produce an action, such as   
   holding an item between finger and thumb, is necessary for predicting   
   the effects of that action in others," said Garcia-Pelegrin, recently   
   appointed an assistant professor at the National University of Singapore.   
      
   The French drop is often the first trick any budding magician sets out   
   to master.   
      
   A coin is displayed in one hand. The other hand reaches over and grabs   
   it. The palm of the second hand faces inwards, with the magician's thumb   
   concealed behind fingers.   
      
   The audience knows the thumb is lurking -- ready to grip -- so assumes   
   the coin has been taken when it is no longer visible. Their attention   
   follows the second hand, only to find it empty at "the reveal." The   
   magician had secretly dropped the coin into the palm of the original hand.   
      
   Food morsels replaced coins for the monkeys, and were given as rewards --   
   but only if the animals guessed the correct hand. Scientists predicted   
   that monkeys with opposable thumbs would act like human audiences:   
   assume the hidden thumb had grabbed the item, and choose the wrong hand.   
      
   They repeatedly performed the French drop on 24 monkeys. Eight capuchins   
   were dazzled with peanuts, eight squirrel monkeys with dried mealworms,   
   and eight marmosets with marshmallows.   
      
   Capuchins are famed for dexterity, and use stone tools to crack nuts in   
   the wild. They can waggle each finger, and have opposable thumbs allowing   
   "precision grip" between thumb and forefingers.   
      
   The capuchins were regularly fooled by the French drop (81% of the   
   time). They mostly chose the empty second hand, and experienced a paucity   
   of peanuts as a result.   
      
   Squirrel monkeys are much less dextrous than capuchins, with limited   
   thumb rotation, but can oppose their thumbs. As such, they are still   
   familiar with a hidden thumb interacting with fingers. However, they   
   cannot perform a 'precision grip' in the same way as capuchins and humans.   
      
   Yet squirrel monkeys were routinely misled by mealworms that seemingly   
   vanished (fooled 93% of the time). "Squirrel monkeys cannot do full   
   precision grips, but they were still fooled. This suggests that a monkey   
   doesn't have to be expert in a movement in order to predict it, just   
   roughly able to do it," said Garcia- Pelegrin.   
      
   Marmosets do not have opposable thumbs. Their thumbs align with their   
   fingers to make five equidistant digits, ideal for climbing thick   
   tree trunks.   
      
   Marmosets were rarely taken in by magic (just 6% of the time). They   
   simply chose the hand in which the marshmallow was initially placed,   
   and stuck with it.   
      
   Previous work from the Cambridge team shows that species without hands   
   at all, in this case birds from the corvid family, namely Eurasian jays,   
   make similar choices as marmosets when confronted with the French drop.   
      
   The team also tried nullifying the tricks by actually completing the   
   hand-to- hand transfers, instead of misdirecting with a French drop. This   
   time, the capuchins and squirrel monkeys anticipated correctly and dined   
   out, and the marmosets missed out.   
      
   Finally, the scientists devised their own version of the French drop,   
   which they call the "Power drop." It utilises a hand action that all the   
   monkey species can perform -- essentially a full fist grab. The power   
   drop fooled all of the monkey species the vast majority of the time.   
      
   "There is increasing evidence that the same parts of the nervous system   
   used when we perform an action are also activated when we watch that   
   action performed by others," said Prof Nicola Clayton FRS, senior author   
   of the study from Cambridge's Department of Psychology.   
      
   "This mirroring in our neural motor system might explain why the French   
   drop worked for the capuchins and squirrel monkeys but not for marmosets."   
   "It's about the embodiment of knowledge," added Clayton. "How one's   
   fingers and thumbs move helps to shape the way we think, and the   
   assumptions we make about the world -- as well as what others might   
   see, remember and anticipate, based on their expectations."  "Our work   
   raises the intriguing possibility that an individual's inherent physical   
   capability heavily influences their perception, their memory of what they   
   think they saw, and their ability to predict manual movements of those   
   around them."  Another co-author of the study, Clive Wilkins, Artist   
   in Residence at Cambridge's Department of Psychology, is a professional   
   magician and Member of the Magic Circle.   
      
   Video: https://youtu.be/bUji-1Q4UgE   
       * RELATED_TOPICS   
             o Mind_&_Brain   
                   # Smoking_Addiction # Psychology # Psychedelic_Drugs   
                   # Memory   
             o Plants_&_Animals   
                   # Monkeys # Apes # Endangered_Animals # Animals   
       * RELATED_TERMS   
             o Illusion_of_control o Hominidae o Howler_monkey o Monkey o   
             Double_blind o Adult_stem_cell o Flying_squirrel o Hallucination   
      
   ==========================================================================   
   Story Source: Materials provided by University_of_Cambridge. The original   
   text of this story is licensed under a Creative_Commons_License. Note:   
   Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Elias Garcia-Pelegrin, Rachael Miller, Clive Wilkins, Nicola   
      S. Clayton.   
      
         Manual action expectation and biomechanical ability in three   
         species of New World monkey. Current Biology, 2023 DOI:   
         10.1016/j.cub.2023.03.023   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/04/230404114216.htm   
      
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