These posts make more sense when read in order.
Please click here for the first article in this series to enter the rabbit hole.
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| 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.
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| 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). |
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| 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.
Click here for the next article in this series:
[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,
[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.
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