Shepard elephant

The Shepard elephant, also known as L'egs-istential Quandary or the impossible elephant is an optical illusion, of the type impossible object, based on figure-ground confusion. As its creator Roger Shepard explains:[1]

The elephant…belongs to a class of objects that are truly impossible in that the object itself cannot be globally segregated from the nonobject or background. Parts of the object (in this case the elephant’s legs) become the background, and vice versa.

Poster showing Shepard elephant (4 legs, 4 feet)
Stanford psychologist Roger Shepard (March 2019), who first published this paradox in 1990.

History

Shepard first published this optical paradox in his 1990 book Mind Sights (page 79) giving it the name "L'egs-istential Quandary".[2] It is the first entry in his chapter on "Figure-ground impossibilities". The pen-and-ink drawing is based on a dream Shepard had in 1974, and on the pencil sketch he made when he woke up.[2]

Interpretation
Blivet illusion, another impossible figure based on figure-ground confusion

The image is widely reproduced and discussed. Brad Honeycutt, author of Exceptional Eye Tricks, calls the Shepard elephant "one of the most famous and classic optical illusions."[3]

The MIT Encyclopedia of the Cognitive Sciences classifies it under "Illusions of Interpretation" as an example of "Impossible Pictures", saying, "Impossible figures embody conflicting 3D clues...Shepard's elephant (figure 2) confuses its legs with the spaces in between. Local votes about depth are not properly integrated."[4]

The Oxford Companion to Consciousness suggests as a way to understand "Shepard’s many-legged elephant": "try slowly uncovering the elephant from the top, or from the bottom." (If you cover the bottom of the drawing, you see the top of an elephant with four legs. If you cover the drawing's top, you see four elephant feet, plus trunk and tail.)[5]

Al Seckel, who devotes Chapter 18 of his book Masters of Deception to Roger Shepard, draws a contrast between Shepard's elephant and the impossible trident (aka the "blivet" or "Devil's tuning fork"). Although an impossible trident has a closed edge, Seckel says the "conspicuous line discontinuity" of the elephant's tail is necessary to avoid a "counting paradox": a blivet is an imaginary object, but everyone knows an elephant has exactly four legs and exactly four feet.[6]

Influence
Derivative version of Shepard elephant (4 legs, 5 feet)

The Shepard elephant has attracted interest outside scholarly sources. Author Clive Gifford included it in his 2013 book for children Eye Benders, and told The Guardian it is one of his favorites.[7]

Sometime before 2012, someone created a modified version of the Shepard elephant. The modified elephant has an extra hind leg, with foot attached, made by extending the curved line that Shepard left ambiguous (to look like either the top of a leg or the end of a tail.) This modified image, which now has four legs but five feet, was circulated as "How many legs does this elephant have?"[8][9][10]

The Shepard elephant has also inspired some other derivative works. Dutch psychologist Hugo Schouppe made a video, showing how GIMP can be used to reverse-engineer the elephant illusion, moving its feet so that each one connects to a leg.[11] The OpticalSpy website also cited the Shepard elephant as inspiration for manipulating a photograph of an Indian elephant to give it six legs.[12]

See also

References
  1. Shepard, RN (1990). Mind Sights: Original visual illusions, ambiguities, and other anomalies, with a commentary on the play of mind in perception and art. W.H. Freeman and Company. p. 143. ISBN 978-0716721345. The elephant…belongs to a class of objects that are truly impossible in that the object itself cannot be globally segregated from the nonobject or background. Parts of the object (in this case the elephant's legs) become the background, and vice versa.
  2. Rock, Andrea (2009). Dream: The Mind at Night: The New Science of How and Why We Dream. Basic Books. p. 137. ISBN 9780786739196. This drawing, entitled L'egs-istential Quandary, sprang from a visual image that came to scientist Roger M. Shepard just before he awakened one morning in 1974. The quick pencil sketch he made when he awoke became the basis for this ink drawing, for which Shepard holds the copyright.
  3. Honeycutt, Brad (March 9, 2012). "Impossible Elephant". AnOpticalIllusion.com. Retrieved March 11, 2019. ..one of the most famous and classic optical illusions of all time. While most people know it simply as the "impossible elephant," the actual title of the work is "L'egs-istential Quandary."
  4. Wilson, Robert Andrew; Keil, Frank C (2001). The MIT Encyclopedia of the Cognitive Sciences. MIT Press. p. 386. ISBN 978-0262731447. Shepard's elephant (figure 2) confuses its legs with the spaces in between. Local votes about depth are not properly integrated. Impossible objects cannot be consistently painted with colors.
  5. Bayne, Tim, ed. (2014). The Oxford Companion to Consciousness. Oxford University Press. p. 366. ISBN 978-0198569510.
  6. Seckel, Al (2004). Masters of Deception: Escher, Dalí & the Artists of Optical Illusion. Sterling Publishing Company, Inc. p. 291. ISBN 9781402751011. To avoid the counting paradox with the number of legs, Shepard introduced the more conspicuous line discontinuity at the far right.
  7. Gifford, Clive (November 17, 2014). "The best optical illusions to bend your eyes and blow your mind – in pictures". The Guardian. Retrieved February 5, 2019. Famous impossible images include the Penrose staircase and this little beauty, courtesy of renowned cognitive scientist and author of Mind Sights, Roger Newland Shepard. With his usual love of a quick joke, Shepard entitled the illusion L'egs-istential Quandary.
  8. Schouppe, Hugo (July 23, 2012). "The elephant illusion (R. Shepard)". CogPsy (archived). Archived from the original on July 4, 2013. Retrieved March 11, 2019. On several websites, a slightly modified version of the [Shepard elephant] illusion is presented with the question "How many legs do you count?". After a few moments of thought, you certainly can figure out what is wrong and how the artist has done it. In fact, it's rather easy and Shepard gives us a clue by omitting the left back foot. Each foot is displaced to the left.
  9. "The Elephant Illusion". BrainPages. 29 August 2012. Retrieved March 11, 2019. There's something not quite right about the elephant below. Can you see it? How many legs does it really have? The elephant illusion is an adaptation of the original which was created by Roger Shepard and published in his book Mind Sights (1990, WH Freeman & Co).
  10. Shaw, Gabi (May 23, 2018). "20 classic optical illusions that stump everyone". Insider. Retrieved March 11, 2019. Can you tell how many legs this elephant has? If looking at the legs is giving you a headache, you're not alone.
  11. Schouppe, Hugo (July 22, 2012). "Shepard's L'egs-istential Quandary (elephant) illusion". YouTube. Retrieved March 11, 2019. Famous cognitive illusion by Roger Shepard. Added interactivity by Hugo Schouppe.
  12. "Elephant Illusion". OpticalSpy.com. December 7, 2018. Retrieved March 11, 2019. How many legs has this elephant got? Well six of course, it is a special six legged Indian elephant designed by us. We wondered what a real elephant would look like if it was similar to the old favourite optical illusion shown on the left here. So just for a bit of fun we made one.
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