Filling in Gaps, Tricking the Eye

image012Scientific American’s Mind
 magazine, an offshoot of the original SA publication, has a regular optical illusion feature that I always find fascinating. A while back it also featured an article highlighting skills possessed by the human eye that computers can’t duplicate. It was titled “Reading between the Lines: How We See Hidden Objects,” and written by one of my favorite scientific authors, Vilayanur S. Ramachandran and his wife, Diane Rogers-Ramachandran.

V.S. Ramachandran is the author of several books including most recently, The Tell-Tale Brain: A Neuroscientist’s Quest for What Makes Us Human. He is Director of the Center for Brain and Cognition and Distinguished Professor with the Psychology Department and Neurosciences Program at the University of California, San Diego, and a charming interview subject.

The Scientific American Mind article ( noted that when an object is partially hidden, the brain deftly reconstructs it as a visual whole. It used as an example our view of “slices” of a dog behind a picket fence. Our brain immediately recognizes a whole dog behind the fence slats, but it is extremely hard to program a computer to do the same.

An example of this ability was devised as an optical illusion by Italian psychologist Gaetano Kanizsa decades ago. In the first view at left, you see what the article authors describe as “a set of ‘chicken feet’ arranged geometrically.” When you add a set of opaque diagonal bars, as in the second view, “a three-dimensional cube springs into focus seemingly by magic, the chicken feet becoming cube corners.”

image014               image015

image017Mr. Kanizsa also experimented with a complementary skill, the brain’s tendency to see the full outline of a nonexistent object, as occurs in his classic triangle illusion where we see a white triangle partially covering three black disks, although no triangle is actually drawn there.

  • You can learn more about or purchase The Tell-Tale Brain: A Neuroscientist’s Quest for What Makes Us Human, here.
  • If you just want to have fun tricking your eye with optical illusions, Al Seckel is one of my favorite authors, and here’s one of my favorite books: The Ultimate Book of Optical Illusions,
  • And here’s one of my favorite websites:


This entry was posted in Uncategorized. Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *