Our Perceptions are Distorted (What is Real? 3)

 

These posts make more sense when read in order.

Please click here for the first article in this series to enter the rabbit hole.

 

Not only is our perception enhanced, it’s also distorted. An example of this is when frightened people see dangerous objects—such as snakes, spiders, and guns—as being much larger than they actually are. Experiments have shown that we see objects that we desire as being closer to us than they really are, while undesirable things look like they’re farther away. I suspect we see dangerous objects as being closer than they actually are, because when you focus on something, that object looks larger than it truly is, whether it’s a bull’s-eye, a golf putting hole, or a tennis ball flying towards you. And if you’re out-of-shape or carrying a heavy box, the stairs actually look steeper to you.[1]

Your brain changes how large or small an object—or part of an object—appears based on whether it’s surrounded by larger or smaller objects (the Ebbinghaus and Ponzo illusions). It fills in any missing parts of lines or objects (amodal completion). It creates objects that aren’t there (modal completion and the Hermann grid illusion). It gives static pictures the illusion they are moving, from slow rotation to rapid shimmering (the Hering illusion, among others).

The Necker Cube looks 3-dimensional, even though it’s not, and our perception can switch it from the upper-right square being forward to having the lower-left square closer to you.

There are many 2-D pictures that look 3-D. Some, like the Necker Cube, appear as if they are coming towards you or going away from you, or they shift back and forth between these two views. And then there are the many impossible objects depicted by Dutch artist M.C. Escher and Swedish artist Oscar Reutersvärd.

Our brains also enhance colors, using our memories of colors to make stop signs and apples appear redder and bananas yellower than they actually are so we can more easily identify them.

The full moon illusion is a good example of how your brain alters what you see. When you see the moon right above the horizon, it looks huge. Later, when it’s at its zenith, it looks tiny, but it’s actually the same size. It’s your brain that expands and shrinks the moon based on visual cues which make it seem closer or farther.

People have a hard time believing this, but if you cut a hole in a piece of paper and hold it to one of your eyes so that it blocks the horizon from that eye, you’ll see a small moon with one eye and a large one with the other, but of course it’s the same moon.

In addition, the moon looks smaller in photos because seeing with two eyes give us a broader field of vision and the curvature of our retinas makes the objects we focus on appear larger.[2]

Many of our perceptions of the world are relative and not based on the world’s actual characteristics. In 1690 British philosopher and medical researcher, John Locke, mentioned a version of a now popular demonstration to illustrate how our sense of temperature is not based on actual temperature. In other words, how our feelings of hot and cold are relative, and actually depend on what our receptors or brains have adjusted to.

To demonstrate this, take three large bowls of water—one hot, one room temperature, and one icy. Placing one hand in the hot water and the other in the icy water, they should begin to feel about the same after a while. Once your hands have adjusted, place them both in the bowl of room temperature water. The water will feel cold to one hand and hot to the other. I recall doing this experiment as a kid and it is a strange sensation since the room temperature water feels so different to each hand.

For reasons we’ve yet to understand, we distort our own body image. An experiment at the University College London found that people generally think their hands are wider and shorter than they really are.[3] There are many more that I’ve written about in several chapters elsewhere, but have yet to publish. Suffice it to say, such misperceptions vary among people and may contribute to disorders like anorexia nervosa.

 

Alice in Wonderland Syndrome

“What a curious feeling!” said Alice. “I must be shutting up like a telescope![...] Now I’m opening out like the largest telescope that ever was! Good-bye, feet!”

—Alice in Alice’s Adventures in Wonderland, 1865

Alice in Wonderland Syndrome is an actual ailment. Usually found in children, its sufferers experience some rather odd spatial distortions. Like Alice, you may suddenly have the feeling you are closing up or opening out like a telescope. Or you may feel like you are tiny and the world is huge, or vice versa. Or you might feel like just your head is huge or your hands are long and thin. The distortions can involve other senses. The ground might feel spongy when you walk on it. Time might run fast or slow. Sounds may be distorted.

“The first time it happened,” wrote Robin Tricoles in The Atlantic, “I was 8. I was tucked in bed reading my favorite book when my tongue swelled up to the size of a cow’s, like the giant tongues I had seen in the glass display case at the neighborhood deli. At the same time, the far wall of my bedroom began to recede, becoming a tiny white rectangle floating somewhere in the distance. In the book I was holding, the typeface grew vast on the page.”[4]

Although these misperceptions could indicate a serious problem, usually they are fleeting and harmless. Still, they can be very disconcerting or even frightening. This syndrome is not a sign of insanity even though it includes hallucinations. In fact, most hallucinations are not associated with insanity. We have them all the time, often without realizing it. And we have more of them as we age, for various reasons I’ll touch on later.

Pull My Finger

Like something out of a cartoon, an experiment found that if someone pulls on your finger as you hear a sound that rises in pitch, you’ll then think your finger is longer than it actually is.[5]

There are many ways our minds distort our body image. Studies show that when using tools our body image adjusts to include the tool as if it were part of us. The Third Hand Illusion (or Rubber-Hand Illusion) is an extreme version of this. It gives you the spooky feeling that a fake hand or someone else’s hand is actually your own hand. This classic experiment was first performed by psychiatrists Matthew Botvinick and Jonathan Cohen at the University of Pittsburgh in 1998, and it’s something you can easily do yourself.

Probably the easiest way is to get two of your friends to help you. Normally scientists would name them Alice and Bob (for A and B). That’s dull, so throughout these posts I’ll use Alice (from Alice in Wonderland) and Bob Marley. So, have Bob Marley—or a friend who looks like him—sit behind you and place his left hand on the table in front of you with his left arm between your body and your left arm. Place your left hand on the table to the left of Marley’s hand and then stand up a piece of cardboard or other barrier so your left hand is hidden from view.

Fang, et al.

Now have Alice, sitting opposite from you, touch both your left hand and Bob’s left hand in the same spot. She can use most any object. I’ve seen people use paint brushes or a wire coat hanger bent to form an upside-down “V” shape, or she can just use the tips of her index fingers. The taps and strokes should be random and not in any pattern, but they must be identical for Marley’s hand and for yours. It takes from 20 seconds to a few minutes for the illusion to kick in.

What you feel is Alice’s right index finger touching your left hand, but what you see is her left finger touching Bob’s hand. The amazing thing is that what you experience is that Bob’s hand becomes your hand. If Alice starts tapping and then stops tapping your hand, while continuing it with Bob’s, you will feel a few more taps even though your hand is no longer being touched.

If you only have one friend available, the experiment still works if you use a photograph of a hand instead of a real one, or an inflated rubber glove. In fact, it sometimes it even works if you use a shoe.[6] It also works with amputees if their stumps are touched at the same time as the fake hand.[7] Researchers usually use a rubber hand. If the fake hand is removed and Alice taps the air where it would be, while tapping your hand that’s out of sight, then you’ll experience having a phantom limb.[8]

Taking the fake hand away and tapping the table, makes some people feel the table had become part of their body.[9] Researchers have even placed two rubber hands in the subject’s view which created the illusion that the subject’s left hand was in two places at once.[10]  They have also made people think they had a sixth finger and that it was longer than the rest, causing one subject to yell, “Witchcraft!”[11] A different illusion using virtual reality made people think their right arm was four times as long as it actually was.[12] Your brain can do interesting things with your senses.

A similar version of this illusion is done with your left arm in full view. This gives you the feeling that you have three arms.[13] This is called the Beeblebrox Illusion—named after Zaphod Beeblebrox, a character with three arms in Douglas Adams’ The Hitchhiker’s Guide to the Galaxy—a humorous series of books, radio shows, TV series, movies, etc. that are extremely popular among scientists, though not quite as popular as Alice in Wonderland is.

It’s easy to think of this as a subtle illusion, but it’s not. When one of the original scientists who discovered the Third Hand Illusion first tried it, he was so shocked that he threw the false hand across the room.[14] In a version of this experiment that was conducted at BarcelonaTech in Spain by a researcher using a computerized 3-D display of an arm, once the illusion kicked in, she rotated the display 90 degrees, causing the volunteer’s shoulder muscles to spasm as if their arm was being twisted.[15]

If you use a rubber hand or a picture of a hand and you’re a fan of Penn and Teller, once the illusion has kicked in, have Alice suddenly stab the fake hand with a steak knife and see how far you jump from the table...even when you know it’s coming.[16]

Neuroscientist Vilayanur Ramachandran and philosopher William Hirstein created in interesting illusion by seating a blindfolded subject with another person sitting directly in front of them so that the person in front had their back to the subject. The researchers took the subject’s index finger and reached it around to touch the tip of the nose of the person sitting in front of them, while one researcher simultaneously touched the subject’s nose. Within a few seconds the subject felt as if their nose was stretched out like Pinocchio’s.[17]

These illusions arise from the brain’s attempt to reconcile conflicting sensory inputs. In the Third Hand Illusions, the brain sides with the dominant sense (vision) over the lesser sense (touch). Similarly, when there’s a conflict between what your two eyes are seeing, your brain rejects the information from one of your eyes.[18] Such suppression is also responsible for the ventriloquist effect. Ventriloquists do not project their voices to a different location. The illusion arises from seeing the dummy’s lips move while the ventriloquist’s are still. Vision dominates hearing, so your brain moves the sound to match what you see.

The Pinocchio illusion shows that even when only one sense is involved, the subconscious will sacrifice the integrity of the body map to conform with unusual sensory input. In spite of the fact that your nose has never suddenly grown to phenomenal lengths before, your brain is ready to accept that it has when that’s what your senses seem to be telling you. Thus we feel like a fake hand is ours or that we have a third arm.

This is a real effect. The disowning of the real hidden hand can be detected by a sudden drop in that hand’s temperature. And when the fake hand is threatened, there’s a change in the real hand’s galvanic skin response showing that the subject thinks the fake hand is real.

Oddly enough there was even one study at Neuroscience Research Australia which appears to indicate that the body’s immune system decreases functioning in the disowned hidden left arm and that the amount of decrease is related to the strength of the illusion.[19]

I find this astonishing. How could the brain’s body map influence the immune cells so quickly, making them think their arm is no longer part of their body? And why doesn’t immunity fail in people with Body Integrity Identity Disorder, who insist one of their limbs is not really part of their body? It will be interesting to see if the results from this study are confirmed.

So, you don’t have to experience Alice in Wonderland Syndrome to feel parts of your body change shape, become distorted, or vanish altogether. All you need is a friend, a rubber hand, and a knife.

Frank Durgin of Swarthmore College in Pennsylvania, who made people’s hands feel heat just by shining a laser pointer on the fake hand, said, “It’s obvious the hand is rubber—no one is fooled at all. But if your brain decides it’s your hand, all the conscious awareness in the world won’t change it.”[20]

These are somewhat extreme examples of the subtle things our brains are doing to our perceptions every day. We just don’t notice it because we assume our perceptions are accurate. If we do notice something unusual, we tend to look for other explanations. The supernatural is a common fall-back explanation for things we can’t explain or don’t understand.

A Collaborative Effort

A Ugandan scientist at work studying fish. Bruno Ashimwe Winks (cropped).

One of the great things about science is that is global. Scientists from all over the world work together make momentous discoveries. Country boundaries and politics are discarded, or at least overlooked, in the pursuit of knowledge. Many studies, research, and experiments are collaborative efforts involving scientists from different countries. Many spend sabbaticals or spend several years working and learning in other parts of the world to gain knowledge, experiences, and alternate perspectives that they wouldn’t be able to pick up at home. This has the effect of broadening one’s worldview—reaching past prejudices and political propaganda.

Not only does this enhance research and lead to new discoveries, it demonstrates how people from different cultures can work together. Few people outside of scientific circles realize the extent of these collaborations. For example, in 2017, nearly 45% of all scientists and engineers in the U.S. were foreign born, mostly from India and China. Of those with doctorates in engineering, 57% were born outside the United States.[21] And more than 40% of American-based Nobel Prize winners are immigrants. Of course there are also many American scientists working elsewhere in the world.

Personally, I find it refreshing to know that there are endeavors which transcend the limited views most people have of the world.

 

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Creating Our Perceptions

 

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[1] Piercarlo Valdesolo, “The Neuroscience of Distance and Desire”, Scientific American, June 15, 2010, https://www.scientificamerican.com/article/neuroscience-of-desire/.

And Association for Psychological Science, “Seeing isn't believing”, ScienceDaily, September 7, 2011, http://www.sciencedaily.com/releases/2011/09/110907144014.htm.

And Valerie Ross, “Closing the Gap”, Scientific American Mind, Aug. 8, 2010, vol. 21, no. 3, p. 7.

And Andrea Anderson, “Towering Targets”, Scientific American Mind, July-August 2011, vol. 22, no. 3, p. 6.

Also, Colorado State University. “Pong paddles and perception: Our actions influence what we see: A new study faces head-on the notion that previous experimental subjects have been victims of response bias”, ScienceDaily, January 3, 2018. www.sciencedaily.com/releases/2018/01/180103111407.htm, citing Jessica K. Witt, Nathan L. Tenhundfeld, Michael J. Tymoski, “Is There a Chastity Belt on Perception?”, Psychological Science, 2017; 095679761773089, https://doi.org/10.1177/0956797617730892.

[2] Edd Gent, “Video games have been getting perspective wrong”, New Scientist, no. 3428, March 4, 2023, p. 11, and a longer version as “Video games have been getting perspective wrong, but now there's a fix”, February 24, 2023, https://www.newscientist.com/article/2360848-video-games-have-been-getting-perspective-wrong-but-now-theres-a-fix/, citing Nicole Ruta, Joanna Ganczarek, Karolina Pietras, Alistair Burleigh, and Robert C. Pepperell, “Non-metric Distance Judgements Are Influenced by Image Projection Geometry and Field of View.” PsyArXiv. February 23, 2023, https://doi.org/10.31234/osf.io/7xack.

[3] Anonymous, “Brain ‘distorts own body image’ ”, BBC News, June 15, 2010, https://www.bbc.com/news/10310571.

[4] Robin Tricoles, “Objects in Brain May Be Bigger Than They Appear”, The Atlantic, March 9, 2015, https://www.theatlantic.com/health/archive/2015/03/objects-in-brain-may-be-bigger-than-they-appear/387064/.

[5] Ana Tajadura-Jiménez, Maria Vakali, Merle T. Fairhurst, Alisa Mandrigin, Nadia Bianchi-Berthouze, and Ophelia Deroy, “Contingent sounds change the mental representation of one’s finger length”, Scientific Reports, vol. 7, article no. 5748, July 18, 2017, https://doi.org/10.1038/s41598-017-05870-4.

[6] Georg Goldenberg, “Body Perception Disorders” in Vilayanur Ramachandran, ed., Encyclopedia of the Human Brain, New York, NY: Academic Press, 2002, vol. 1, p. 447.

[7] Peter Aldhous, “Brain trick makes robot hand feel real”, New Scientist, no. 2692, January 24, 2009, p. 15, www.newscientist.com/article/mg20126924.900-brain-trick-makes-robot-hand-feel-real.html, citing Brain, brain.oxfordjournals.org/content/131/12/3443, https://doi.org/10.1093/brain/awn297.

Also Karolinska Institutet, “Amputees Can Experience Prosthetic Hand As Their Own”, ScienceDaily, December 13, 2008, www.sciencedaily.com/releases/2008/12/081211081809.htm, citing Henrik Ehrsson, Birgitta Rosén, Anita Stockselius, Christina Ragnö, Peter Köhler, and Göran Lundborg, “Upper limb amputees can be induced to experience a rubber hand as their own”, Brain, (2008) 131, 3443-3452.

[8] Patrick Russell, “Anyone can have a phantom limb”, New Scientist, no. 2913, April 20, 2013, p. 17, and a longer version as “Non-amputees given an invisible phantom limb”, www.newscientist.com/article/dn23374-nonamputees-given-an-invisible-phantom-limb.html, citing Arvid Guterstam, Giovanni Gentile, and H. Henrik Ehrsson, “The Invisible Hand Illusion: Multisensory Integration Leads to the Embodiment of a Discrete Volume of Empty Space”, Journal of Cognitive Neuroscience, July 2013, vol. 25, no. 7, pp. 1078-1099, www.mitpressjournals.org/doi/abs/10.1162/jocn_a_00393#.VI6f5Xu22M0, https://doi.org/10.1162/jocn_a_00393.

[9] Graham Lawton, “Mind tricks: Six ways to explore your brain”, New Scientist, no. 2622, September 19, 2007, https://www.newscientist.com/article/mg19526221-300-mind-tricks-six-ways-to-explore-your-brain/.

[10] Graham Lawton, “Whose Body is that Anyway?”, New Scientist, no. 2699, March 21, 2009, pp. 36-37, and as “Body illusions: The Beeblebrox illusion”, www.newscientist.com/article/mg20127002.600-body-illusions-the-beeblebrox-illusion.html.

[11] Matthew Hutson, “Phantom Finger”, Scientific American, vol. 326, no. 3, March 2022, p. 15, and as “Researchers Make a Phantom Sixth Finger Grow and Shrink”, https://www.scientificamerican.com/article/researchers-make-a-phantom-sixth-finger-grow-and-shrink/, https://doi.org/10.1038/scientificamerican0322-15.

[12] Universidad de Barcelona, “Using virtual reality an arm up to three or even four times the length of a real arm can be felt as if it was the person’s own arm”, ScienceDaily, July 24, 2012, www.sciencedaily.com/releases/2012/07/120724104314.htm, citing Konstantina Kilteni, Jean-Marie Normand, Maria V. Sanchez-Vives, and Mel Slater, “Extending Body Space in Immersive Virtual Reality: A Very Long Arm Illusion”, PLoS ONE, 2012; 7 (7): e40867, https://doi.org/10.1371/journal.pone.0040867.

[13] A. Guterstam, V.I. Petkova, and H.H. Ehrsson, “The Illusion of Owning a Third Arm”, PLoS ONE, 2011, 6(2): e17208, www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0017208, https://doi.org/10.1371/journal.pone.0017208.

[14] Anonymous, “There’s the Rub”, Discover, June 1998, p. 21.

[15] Graham Lawton, “Whose Body is that Anyway?”, New Scientist, no. 2699, March 21, 2009, pp. 36-37, and as “Body illusions: The virtual body”, www.newscientist.com/article/mg20127002.700-body-illusions-the-virtual-body.html.

[16] Eric Haseltine, “Phantom Sensations”, Discover, vol. 23, no. 5, May 2002, p. 88.

[17] Georg Goldenberg, “Body Perception Disorders” in Vilayanur Ramachandran, ed., Encyclopedia of the Human Brain, New York, NY: Academic Press, 2002, vol. 1, p. 447.

[18] University of Chicago, “Color Plays Musical Chairs In The Brain”, ScienceDaily. October 2, 2009, http://www.sciencedaily.com/releases/2009/10/091001164231.htm.

[19] Phil Corlett, “Scicurious Guest Writer! Sleight of Hand, Sleight of Mind: Illusions, Delusions and the Immune System”, Scientific American, Jan. 30, 2013, http://blogs.scientificamerican.com/scicurious-brain/2013/01/30/scicurious-guest-writer-sleight-of-hand-sleight-of-mind-illusions-delusions-and-the-immune-system/, citing N. Barnsley, et al., “The rubber hand illusion increases histamine reactivity in the real arm”, Current Biology, 21, 2011, R945-946 www.cell.com/current-biology/abstract/S0960-9822%2811%2901200-0, https://doi.org/10.1016/j.cub.2011.10.039,.

[20] Graham Lawton, “Mind tricks: Six ways to explore your brain”, New Scientist, no. 2622, September 19, 2007, https://www.newscientist.com/article/mg19526221-300-mind-tricks-six-ways-to-explore-your-brain/.

[21] National Center for Science and Engineering Statistics, “The State of U.S. Science and Engineering 2020”, National Science Board, January 2020, https://ncses.nsf.gov/pubs/nsb20201/u-s-s-e-workforce#foreign-born-scientists-and-engineers.

And National Center for Science and Engineering Statistics, “Foreign-Born Students and Workers in the U.S. Science and Engineering Enterprise” (flyer), National Science Board, 2020, https://www.nsf.gov/nsb/sei/one-pagers/Foreign-Born.pdf.

Misperceiving Reality (What is Real? 2)

 

These posts make more sense when read in order.

Please click here for the first article in this series to enter the rabbit hole.

 

Our brains interpret the cloud on the left as a rabbit that's not really there, but that really is Mt. Fuji on the right. © John Richard Stephens, 2024.

Windows to  the World? Not Quite.

The reason why our perceptions seem so real, according to neuroscientist David Eagleman of Baylor College of Medicine in Houston, Texas, is that our brains are “good at extracting patterns from our environment and assigning meaning to them.”[1]

University of Bristol, U.K. neuroscientist Bruce Hood wrote in his book The Self Illusion, “Our brain simulates the world in order to survive in it. This simulation is remarkable because much of the data that needs processing are corrupted. And yet, our brain fills in missing information, interprets noisy signals, and has to rely on only a sample of everything that is going on around us. We don’t have sufficient information, time, or resources to work it all out accurately so our brains make educated guesses to build our models of reality. That working-out includes not only what’s out there in the external world but also what is going on in the internal, mostly subconscious, workings of our mind.”[2]

Our senses are constantly assaulted by a barrage of raw data—far more than our brains can process—so we have to whittle it down to what is important for our survival. With vision, for example, measurements indicate that each of the retinas in our eyes register one gigabyte (1,000,000,000 bytes) of data per second, but only about six million signals are sent along to our brains. That’s still way too much information, so our brains filter and process it down to about 100 or less. So in the end, we become aware of only one millionth of the information that retina receives.[3]

For most of us, vision is our primary sense. Because vision is so expensive, there are a lot of incentives to take shortcuts. It’s a continual balance between what you can lose, while maintaining fidelity that’s good enough to ensure survival. So to maintain efficiency, your senses have to do some drastic things.

It’s amazing how our brains do this and we know of several ways it’s accomplished. One of them is by filtering the data and another is by compressing it, similar to how a computer compresses image files. I already mentioned how our retinas cut one gigabyte of data down to 100 bytes. That’s filtering in the eye itself before it’s sent to the brain. A lot more filtering takes place in the brain.

A large portion of our sensory input is cast aside or suppressed before reaching our conscious awareness. You don’t usually feel the clothes you’re wearing or the chair you’re sitting on unless you focus your attention on them, or unless you feel a quarter-of-a-second or longer gap in the stimulus.

Unchanging stimuli fades from your attention. Stare at the X and the Cheshire Cat’s face fades away leaving only it’s smile. Eventually the smile will fade away as well. This is called the Troxler Effect. The Illusions Index (CC BY-NC_SA 4.0).

 

The Invisible Gorilla

 

Arnold Schwarzenegger's stunt double in a scene from Terminator 2.

But we can also be blind to changes. Changes in lighting and shadows can alter the way something looks. This is especially true of faces, so your brain stabilizes what we see so we can still recognize a person when we see them from different angles and under changing lighting conditions. It’s because of this that movie makers can swap out actors with stunt doubles and you will think it’s the same person, even when they don’t look alike. Your brain helps make them look like they’re the same person. Your brain does this to make sense of a chaotic visual world and provide you with continuity, stability, and familiarity.

Harvard University and Kent State University researchers tested subjects who were in the middle of having a conversation by surreptitiously swapping out the person they were talking to, and just over half of the test subjects never noticed.[4]

In the 1980s when I was in the Air Force they sent me to train at the intelligence school for officers. If you are former military, you’ll probably find that very funny and something of an oxymoron, but not all officers went to intelligence school and it wasn’t an attempt at making us smarter. In the armed forces they like to use nicknames, so you have grunts, jarheads, squids, and flyboys (or zoomies). Well, the pilots called us intel weenies.

I was training for operations intelligence, which in the movies is the officer who stands up in front of the pilots and briefs them on the mission they’re about to fly. We had to design flight plans and know all about the terrain, the weather, the target, and the threats they would face.

The training facility had various levels of secrecy and we were only allowed into the areas where we were authorized. There was one classified area where they trained the foreign intelligence officers. I recall there were a lot of Saudis, Indonesians, Malaysians, South Koreans, and Iraqis, since this was before our war with Iraq and no one saw that coming. We tend to forget that Iraq was our ally against Iran right up until the day Iraq invaded Kuwait, which resulted in a short period of puzzlement before Saddam Hussein suddenly became our enemy and the Iraqi officers training at our base had to be sent home.

Anyway, sometime before this the administration wanted to check security so they had two guys dress up in some silly uniforms and wander around that secure area for a couple of hours. Because of all the foreign uniforms, no one noticed them, even though one of them was wearing his son’s badge from Space Camp. Many people saw them, but didn’t really see them.

This is not a bad reflection on the military. These pretend foreigners probably didn't pass through the security checkpoint and the one I met didn't look foreign and would have fit right in, in spite of his wacky uniform. Still, the fact that no one noticed is perfectly normal and is how our brains work. It’s especially common among people who are very busy, working hard, and preoccupied with important duties, as those in the military are. Some people are more aware and observant than others, but even they miss a lot. Something has to stick out and catch our attention before it seems out of place and enters our awareness.

Change blindness and inattentional blindness can cause serious problems in some situations. You can’t pay attention to everything. For some reason our attention can only track about four or five moving objects at a time, so your brain focuses on what it determines is important, and filters out the rest. In fact, it does a lot of filtering. It is surprising how much filtering it does. We can look right at an object and not be aware of it. There's a video that is a striking example of this.

Created by cognitive psychologists Christopher Chabris and Daniel Simons while at Harvard University, the video features six people—three in white shirts and three in black—passing a basketball between them, while moving around. You’re instructed to count how many times the white-shirted people pass the ball.

Follow the instructions. If you don’t follow the instructions, it won’t work. It’s worth taking the quick test. You will be surprised at the result.

Now, I’m about to spoil it for you, so you should stop here and view the video before going on. The effect is stunning if you experience it, but not if you read the spoiler. This is your only chance to experience under the influence of the blue pill. Then they and I will return you to red-pill consciousness.

Spoiler: By focusing on following the basketball, about half the viewers don’t see the gorilla walking across the screen. If you’re one of them, you’ll be flabbergasted when you watch it again ignoring the ball. Halfway through a young woman in a gorilla suit slowly walks into the midst of the people, bangs on her chest like a gorilla, and then slowly walks off the other side of the scene.[5] If you did notice the gorilla, then perhaps you’ll be surprised that so many people don't see it.

This is a demonstration of selective attention and is why most people don't see continuity errors in movies, when objects appear or disappear, move or change color from scene to scene. It's also one reason why you see typos in almost everything you read, even in headlines, and it's why 83% of a group of the radiologists missed an image of a gorilla embedded in X-rays they examined, even though they looked right at it.[6]

Magicians are masters of distraction. They carefully direct your attention so you’re focused on one thing, while they’re actually doing something else. They also use suggestion to encourage you to believe something that’s not happening. In one study experimenters showed a video of a magician bending a key using sleight of hand, the key was then placed on a table while the magician said it was still bending. Forty percent of the subjects said they saw it continue to bend, even though it didn’t.[7]

It's Just an Illusion

Because of the massive amount of information our eyes receive, our perceptual systems simplify our vision in order to process it, but they also actively enhance it—altering the visual information we receive.

One example is that our retinal cells use lateral inhibition—where activated cells inhibit their neighbors—to enhance the contrast of edges. This has the effect of making edges of colors or light stand out so it’s easier for us to spot objects. It also causes us to see a number of optical illusions.[8] And the lateral inhibition of cells is not just found in vision. It’s also used in hearing, touch, and in the brain itself.

There are also cells in the retina that respond differently to black and white in a way that makes white areas appear larger and brighter, while black areas are dealt with normally. This makes white dots look larger and stand out more than dark dots. While we think of white and black as opposites, our visual system processes them as two different things.[9]

Many animals, like us, have cells in their brains that respond only to horizontal lines and others are only triggered by vertical lines, which is why we’re sensitive to crooked picture frames, but this isn’t universal. It depends on the environment in which you were raised. Canadian scientists found that Cree Indians who lived in tepees on the shore of James Bay—between the provinces of Quebec and Ontario—lacked this preference, since their environment contained few horizontal or vertical lines.[10]

The neurotransmitter GABA suppresses details around whatever object we’re focused on. This helps us pick out camouflaged objects from the background. People who are depressed are less able to do this because their GABA levels are reduced.[11] We’re also particularly sensitive to movement by small objects, such as bugs, because that’s also greatly enhanced by our brains.[12]

In the Checker-Shadow Illusion, checkerboard squares A and B are identical shades of gray, as can be seen on the right where they have been extracted and placed on a more neutral background. The illusion of lighting and a shadow tricks our brains. Edward H. Adelson, Massachusetts Institute of Technology, © 1995.

One of the enhancements that I find most striking becomes apparent in the Checker-Shadow Illusion. Shadows pose a particularly difficult problem for visual systems. The variations in brightness and color under different lighting conditions can make it hard to discern objects, so our visual sense has evolved to emphasize perceptual constancy, which means we perceive properties like brightness, color, and size variably and separate from reality.

The Checker-Shadow Illusion demonstrates this by showing that our brains alter the brightness of two squares based on context and their interpretation of lighting. There’s no actual light or shadow in this two-dimensional graphic, but our brains think there is, so they process the image as if it’s a three-dimensional scene with a real shadow created by a light source off to the right.[13]

There’s a similar illusion where a gray circle will look white to us when it’s surrounded by black and looks black when surrounded by white. Without checking it, we wouldn’t know the circle was really gray. Illusions of false luminance like this can actually cause your pupils to dilate or constrict.[14] The illusion isn’t real, but our brains think it is.

How we see things sometimes depends on the context, but it can also be a matter of perspective, such as the Mystery Hill illusions, where cars look like they are coasting up hill, unless you look at it from another perspective and see that it’s actually rolling downhill. The illusion arises when the horizon line appears to be somewhere that it’s not. You’ll find the same effect in anti-gravity mystery houses.

 

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Our Perceptions are Distorted

 

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[1] Helen Thomson, “Try my extrasensory jacket on for size” (interview with David Eagleman), New Scientist, no. 3042, October 10, 2015, pp. 26-28, and as “Go beyond your five senses with my extrasensory jacket”, October 7, 2015, https://www.newscientist.com/article/mg22830420-500-my-smart-vest-will-offer-you-extra-senses/.

[2] Bruce Hood, The Self Illusion, Oxford, UK: Oxford University Press, 2012, pp. xii.

[3] Marcus E. Raichle, “Two views of brain function”, Trends in Cognitive Sciences, vol. 14, no. 4, April 1, 2010, pp. 180-190, https://www.cell.com/trends/cognitive-sciences/fulltext/S1364-6613(10)00029-X, https://doi.org/10.1016/j.tics.2010.01.008.

[4] D.J. Simons and D.T. Levin, "Failure to detect changes to people during a real-world interaction", Psychonomic Bulletin & Review 5, 644–649 (1998), https://link.springer.com/content/pdf/10.3758/BF03208840.pdf, https://doi.org/10.3758/BF03208840.

[5] Christopher Chabris and Daniel Simons, 1999, http://www.theinvisiblegorilla.com/gorilla_experiment.html.

And Christopher Chabris and Daniel Simons, The Invisible Gorilla, New York City: HarperCollins Publishers, 2010.

[5] Trafton Drew, Melissa L.-H. Võ, and Jeremy M. Wolfe, “The Invisible Gorilla Strikes Again”, Psychological Science, vol. 24, July 17, 2013, p. 1848, https://journals.sagepub.com/doi/abs/10.1177/0956797613479386, https://doi.org/10.1177/0956797613479386.

[7] Alok Jha, “Bursting the magic bubble”, The Guardian, July 27, 2005, https://www.theguardian.com/science/2005/jul/28/psychology, citing the work of psychology professor Richard Wiseman of Hertfordshire University, UK, and author of Paranormality, London: Pan, 2015.

[8] James W. Kalat, Biological Psychology, Belmont, CA: Wadsworth Publishing Company, 1981, pp. 151-58.

[9] Qasim Zaidi, “Black and White Aren’t Opposites After All”, Zocalo Public Square, Arizona State University, May 3, 2016, https://www.zocalopublicsquare.org/2016/05/03/black-and-white-arent-opposites-after-all/ideas/nexus/.

[10] Roger Lewin, “Observing the Brain Through a Cat’s Eyes”, Saturday Review/World, October 5, 1974. Reprinted in Anonymous, Annual Editions: Readings in Psychology 75/76, Guilford, CT: The Dushkin Publishing Group, 1975, pp. 37-39.

[11] Jessica Hamzelou, “The world looks different if you’re depressed”, New Scientist, no. 2736, November 28, 2009, p. 14, https://www.newscientist.com/article/mg20427365-000-the-world-looks-different-if-youre-depressed/, November 25, 2009, citing Journal of Neuroscience,  https://doi.org/10.1523/jneurosci.1003-09.2009.

[12] Jordana Cepelewicz, “Your Brain Chooses What to Let You See”, Quanta Magazine, September 30, 2019, https://www.quantamagazine.org/your-brain-chooses-what-to-let-you-see-20190930/.

[13] Edward Adelson, “Checkershadow Description”, MIT, 2010, http://persci.mit.edu/gallery/checkershadow/description.

And G. Thomson and F. Macpherson, “Adelson’s Checker-Shadow Illusion” in F. Macpherson (ed.), The Illusions Index, July 2017, https://www.illusionsindex.org/ir/checkershadow.

[14] Bruce Hood, “Re-creating the Real World”, Scientific American Mind, vol. 23 no. 4, August-September 2012, pp. 42-45.