Aging causes significant changes in visual perception, even in healthy people with no dementia or eye disease. As a result, many people struggle with simple daily activities as they age—things like driving safely, walking on uneven ground or negotiating stairs. Unfortunately, the mechanisms underlying age-related defects in perception are not well understood. Few studies have investigated the kinds of perceptual changes that occur through adulthood, particularly in older individuals, and even fewer have correlated those changes with brain function and eye movements.
But visual illusions have begun to provide some important insights in this area. Because we know that specific ocular or brain mechanisms mediate certain illusions, how our perception of them alters with age provides clues to how aging affects related brain cell populations. These shifts also lay plain that the existence of illusions is not just an accident or mistake of evolution. Illusions are part and parcel of our perception, and their degradation with age—which, let's be clear, makes the observer see the world in a more accurate and less illusory fashion—indicates that some aspects of illusory perception may have enhanced survival. Such an advantage becomes less important as brain function decreases in senescence.
Other types of visual impairments can help us understand neurodegeneration in the aging brain. Yet illusions may stand out above other visual biomarkers because older vision scientists—themselves experts in illusory perception—are acutely aware when their own observations do not match those of their younger experimental test subjects. It is one thing to have back pain, or to lose the ability to run an eight-minute mile, or to have trouble memorizing phone numbers. Those problems are all annoying. But when an amazing new illusion fails to work for your brain—especially when all your younger colleagues are agog—it is downright unnerving. It certainly focuses the mind and makes those neuroscientists wonder if they may be slowly losing theirs.
Lothar Spillmann, currently a visiting professor at the National Taiwan University, is a case in point. Spillmann spent most of his career at the University of Freiburg. Then he turned 65—the German university system's mandatory retirement age—and he had to hit the road to find continued employment abroad. Now 77, he remains a highly productive scientist and serves as an international elder statesman for perceptual science.
As a world leader in his field, Spillman has discovered a number of important misperceptions, including the Ouchi-Spillmann illusion, which produces a motion effect that we described previously in this column. So you can imagine Spillmann's concern when—the same year he retired in Germany—he discovered he was blind to perhaps the most significant illusion of the past two decades, Akiyoshi Kitaoka's Rotating Snakes [below].
This article was originally published with the title "The Age of Illusion" in SA Mind 27, 1, 18-19 (January 2016)
MORE TO EXPLORE
Japanese Optical and Geometrical Art. Hajime Ouchi. Dover Publications, 1973.
Perception of Illusory Movement. Alex Fraser and Kimerly J. Wilcox in Nature, Vol. 281, pages 565–566; October 18, 1979.
Neural Basis for a Powerful Static Motion Illusion. Bevil R. Conway, Akiyoshi Kitaoka, Arash Yazdanbakhsh, Christopher C. Pack and Margaret S. Livingstone in Journal of Neuroscience, Vol. 25, No. 23, pages 5651–5656; June 8, 2005.
Age Effects on the Perception of Motion Illusions. Jutta Billino, Kai Hamburger and Karl Gegenfurtner in Perception, Vol. 38, No. 4, pages 508–521; 2009.
Microsaccades and Blinks Trigger Illusory Rotation in the “Rotating Snakes” Illusion. Jorge Otero-Millan, Stephen L. Macknik and Susana Martinez-Conde in Journal of Neuroscience, Vol. 32, No. 17, pages 6043–6051; April 25, 2012.
The Neuroscience of Illusion. Susana Martinez-Conde and Stephen L. Macknik in Scientific American, Special Edition, Vol. 20, No. 13, pages 4–7; Fall 2013.
ABOUT THE AUTHOR(S)
Stephen L. Macknik is a professor of opthalmology, neurology, and physiology and pharmacology at SUNY Downstate Medical Center in Brooklyn, N.Y. Along with Susana Martinez-Conde and Sandra Blakeslee, he is author of the Prisma Prize-winning Sleights of Mind. Their forthcoming book, Champions of Illusion, will be published by Scientific American/Farrar, Straus and Giroux. Follow Stephen L. Macknik on Twitter Credit: Sean McCabe
Susana Martinez-Conde is a professor of opthalmology, neurology, and physiology and pharmacology at SUNY Downstate Medical Center in Brooklyn, N.Y. She is author of the Prisma Prize-winning Sleights of Mind, along with Stephen L. Macknik and Sandra Blakeslee. Their forthcoming book, Champions of Illusion, will be published by Scientific American/Farrar, Straus and Giroux. Follow Susana Martinez-Conde on Twitter Credit: Sean McCabe