Why Illusions Are A Brain Feature, Not A Bug

Summary

Podcast Summary: Short Wave - "Why Illusions Are A Brain Feature, Not A Bug"

Podcast Information

• Title: Short Wave
• Host/Author: NPR
• Episode: Why Illusions Are A Brain Feature, Not A Bug
• Release Date: July 30, 2025
• Duration: Approximately 12 minutes

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Introduction to Visual Illusions

In the episode titled "Why Illusions Are A Brain Feature, Not A Bug," NPR's Short Wave explores the fascinating world of visual illusions and their significance in understanding human perception. Hosts Emily Kwong and Regina Barber delve into how illusions reveal the intricate workings of the brain, shaping our perception of reality.

The Genesis of Visual Illusions

Emily Kwong introduces the topic with a personal anecdote from Susana Martinez Conde, a renowned neuroscientist:

"So I thought that that was something that I had noticed for the first time ever. And no, it's a very old illusion." [00:55]

Susana Martinez Conde explains her early encounter with the waterfall illusion, or motion aftereffect, highlighting its historical roots:

"Neurons in your visual cortex are sensitive to specific motion directions." [01:14]

She elaborates on the neurological basis of the illusion:

"If you look at water flowing in one direction, those specific neurons that are sensitive to that direction stop firing as much. They almost adapt to the flow." [01:22]

Understanding the Brain’s Perception Mechanism

Susana Martinez Conde provides a deeper insight into how the brain processes visual information:

"And when you look elsewhere, the neurons that are responsive to the opposite direction of motion, those are going to become a lot more prominent in your perception. So that's why you see motion in the opposite direction to the direction that your visual system is adapted to." [01:32]

Emily Kwong further probes into the nature of perception:

"All reality is perceptual, you're saying. It's all filtered by what our brain is telling us." [06:22]

Susana confirms and expands on this notion:

"You never have a direct experience of reality. You've always been inside of your simulation. And your brain structure is so critical to the simulation that Your view of the world, your sense of the world is going to be just so different depending what kind of brain you have." [06:27]

The Illusion of the Year Contest

Susana Martinez Conde and her collaborator, neuroscientist Stephen Macnick, initiated the Illusion of the Year contest to celebrate and discover new visual illusions. Emily Kwong describes the inception of this unique competition:

"Susannah and Steven developed the Illusion of the Year contest. Artists, magicians, any illusion creators can upload a one minute video sharing some kind of novel illusion." [02:40]

Susana reflects on the enduring nature of illusions:

"And I think that it brings together so well the science and the art, because you're not just watching the implementation of a brain principle, of a perception principle, but you're actually watching art." [10:29]

Deep Dive: Rotating Snakes Illusion

One of the key illusions discussed is the Rotating Snakes illusion by Akiyoshi Kitaoka. Emily Kwong describes her personal experience with this illusion:

"It's like six kaleidoscopic looking circles that are made up of smaller, overlapping, different colored circles. And I know they're not moving, but as I focus on one, it looks the others are moving." [07:03]

Susana explains the science behind it:

"These color patches, what's critical to them is not the color itself, but the luminance. So their brightness. And in the proper order, this sequence of patches tricks again, the motion sensitive neurons in your brain into, quote, unquote, believing that there is motion." [07:36]

She further details the role of eye movements in perceiving the illusion:

"All of our eyes jump. They jump every second of every waking hour. So by the time you go to bed, you will have made about 200,000 of these eye jumps in a given day." [08:10]

Award-Winning Illusion: Static Spin

The episode highlights the first-place winner of the Illusion of the Year contest, "Static Spin" by Salita Kadir and Bernard Egger from Germany. Emily Kwong describes the illusion:

"So this is a ballerina, an illustration of a ballerina, and she's rendered entirely in grayscale. She seems to be spinning, right? She's not." [09:53]

Salita Kadir explains the creation process:

"We've taken this 2D illusion into the third dimension by first estimating the depth of the image and then calculating the speed per pixel for a dynamic, lifelike effect." [10:04]

Susana Martinez Conde praises the submission:

"I think that it brings together so well the science and the art, because you're not just watching the implementation of a brain principle, of a perception principle, but you're actually watching art." [10:29]

The Scientific Value of Studying Illusions

Emily Kwong inquires about the importance of illusions in scientific research. Susana Martinez Conde emphasizes their role in understanding consciousness:

"The definition of an illusion is a disconnect between objective reality and subjective perception. Because of this disconnect in illusions between perception and reality, we can, as scientists, go in and analyze the neurons and the brain circuits that support activity, neural activity that matches perception, and those could be part of the neural basis of consciousness." [11:08]

Future of the Illusion Contest

The Illusion of the Year contest is set to continue, welcoming global participants:

"Anybody can participate. You can be an illusion creator and you can participate as a contestant. And you can also participate by voting for the best illusions." [11:57]

Conclusion

The episode concludes with a reflection on the mesmerizing blend of art and science that visual illusions represent. Emily Kwong likens each episode of Short Wave to a combination of science and magic, much like the illusions discussed.

"I like to think of every episode of our show as a combination of science and magic, just like an illusion." [12:08]

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Key Takeaways

• Visual Illusions Reveal Brain Function: Illusions are not flaws but intrinsic features of how our brains process and perceive the world.

• Rotating Snakes and Static Spin: These illusions demonstrate how motion can be perceived in static images through specific patterns and eye movements.

• Illusion of the Year Contest: A platform that bridges art and neuroscience, encouraging global participation and innovation in illusion creation.

• Understanding Consciousness: Studying illusions provides insights into the neural basis of consciousness by highlighting the difference between perception and reality.

Notable Quotes

• "Neurons in your visual cortex are sensitive to specific motion directions." — Susana Martinez Conde [01:14]

• "All reality is perceptual, you're saying. It's all filtered by what our brain is telling us." — Emily Kwong [06:22]

• "I think that it brings together so well the science and the art, because you're not just watching the implementation of a brain principle, of a perception principle, but you're actually watching art." — Susana Martinez Conde [10:29]

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This episode of Short Wave offers an illuminating exploration into the world of visual illusions, showcasing their significance in both scientific research and artistic expression. Through engaging discussions and expert insights, listeners gain a deeper appreciation of the complex relationship between perception, reality, and the remarkable capabilities of the human brain.

Transcript

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[Emily Kwong]

You're listening to short wave from NPR. When Susana Martinez Conde was around 10, she was on a school trip near her hometown of a Corunho, Spain, when she found herself by a river, just staring at the water. But then she noticed something weird as she stared at the river and shifted her gaze to stationary objects nearby, like a rock or a riverbed. It almost looked like those objects were moving too, but in the opposite direction.

[Susana Martinez Conde]

So I thought that that was something that I had noticed for the first time ever. And no, it's a very old illusion.

[Emily Kwong]

In fact, Aristotle was the first person to describe this waterfall illusion, or motion after effect. And as a scientist, Susanna now understands why this happens.

[Susana Martinez Conde]

Neurons in your visual cortex are sensitive to specific motion directions.

[Emily Kwong]

So if you look at water flowing in one direction, those specific neurons that are sensitive to that direction stop firing as much. They almost adapt to the flow.

[Susana Martinez Conde]

And when you look elsewhere, the neurons that are responsive to the opposite direction of motion, those are going to become a lot more prominent in your perception. So that's why you see motion in the opposite direction to the direction that your visual system is adapted to.

[Emily Kwong]

Susannah is a professor of ophthalmology, neurology, physiology and pharmacology at CS Suny Downstate Health Sciences University. And she loves illusions because illusions are perceptual experiences that do not match physical reality. How we see the world is driven entirely by our brains, and illusions really reveal that. She and her collaborator, now husband, neuroscientist Stephen Macnick, made a game of spotting illusions. Whenever they went to professional vision conferences, they always wanted to know what new illusions had been discovered by other vision scientists. Back in 2005, they had this idea.

[Susana Martinez Conde]

Wouldn't it be cool to have an event where we can have all the new illusions come together? And we thought, let's have an illusion contest.

[Emily Kwong]

Susannah and Steven developed the Illusion of the Year contest. Artists, magicians, any illusion creators can upload a one minute video sharing some kind of novel illusion. And Susannah has been genuinely shocked that 20 years later, New illusions are still coming in. Illusions appear to be a fundamental feature of how our brains work, almost like the curtain falling down to reveal the wizard of Oz.

[Susana Martinez Conde]

And they're not the situations in which the brain gets it wrong, so to speak. But illusions are intrinsic to how we construct our perception of the world.

[Emily Kwong]

Today on the show, we get lost or maybe found in the brain magic of visual illusions and reveal the most recent first place winner in the Illusion of the Year contest. I'm Emily Kwong and you're listening to Short Wave from npr.

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[Emily Kwong]

Right, Susana, so today we are going to get lost in the world of illusions. You were saying earlier how this is not a bug, but is in fact just a fundamental fact about how our brains work.

[Susana Martinez Conde]

Why exactly? From the very beginning of the visual path, we were talking about the retina at the back of the eye. And there you already have neurons that are specialized on detecting contrast. So the brain never cares about absolute terms. There is no black, there is no white, there is no big or small. Everything depends on what you're comparing it with. And so this inevitably gives rise to illusions. And so, in fact, I would go beyond to say that we never have 100% correspondence between reality and perception. What we call illusions are those cases in which the discrepancy is most spectacular, that we can no longer ignore it, and in some cases, really important cognitive dissonance. Because we can be in situations in which we know for a fact that what we're seeing is different from what's there, but we cannot force ourselves to see it any differently.

[Emily Kwong]

All reality is perceptual, you're saying. It's all filtered by what our brain is telling us.

[Susana Martinez Conde]

You never have a direct experience of reality. You've always been inside of your simulation. And your brain structure is so critical to the simulation that Your view of the world, your sense of the world is going to be just so different depending what kind of brain you have. And I'm not just talking about individual differences, but your experience of the world is gonna be different from your cat's experience of the world or a bee's experience of the world and so on. These are different brains and realities.

[Emily Kwong]

All right, well, let's talk about two visual illusions. The first one I want to discuss is an image you studied called rotating snakes. It's an example of what's called peripheral drift. It's a still photo that your mind thinks is moving. And I'm looking at it now, rotating snakes. And to describe it, it's like six kaleidoscopic looking circles that are made up of smaller, overlapping, different colored circles. And I know they're not moving, but as I focus on one, it looks the others are moving. What is happening?

[Susana Martinez Conde]

Yes. So the rotating snakes illusion was created by one of the most famous illusion creators, Akiyoshi Kitaoka. And as you change your gaze around the image, these snakes appear to rotate, when in reality the image is perfectly stationary. These color patches, what's critical to them is not the color itself, but the luminance. So their brightness. And in the proper order, this sequence of patches tricks again, the motion sensitive neurons in your brain into, quote, unquote, believing that there is motion. And what we discovered in my laboratory some years ago was the specific type of eye movement that you need to trigger this illusion. And that is the sort of transient eye movements, such as eye jumps. All of our eyes jump. They jump every second of every waking hour. So by the time you go to bed, you will have made about 200,000 of these eye jumps in a given day. And you're only aware of, you know, maybe a dozen of them, if I were to guess. So, you cannot make more jumps on purpose, but what you can do is you can briefly suppress them. And so if you are looking at the rotating snake solution and you choose a single point, like the center of one of the snakes, and try to keep your eyes there as precisely as you can, just fix your eyes as much as you can, you're going to get the snakes to slow down or even stop completely. But if you relax your gaze again, the motion will come right back.

[Emily Kwong]

So you, you announced the winners of the Illusion of the Year contest recently, this month, and I wanted to talk about the winner. And this is a static spin by Salita Kadir and Bernard Egger out of Germany. So this is a ballerina, an illustration of a ballerina, and she's rendered entirely in grayscale.

[Salita Kadir]

She seems to be spinning, right? She's not.

[Emily Kwong]

And it's like the edges of her are almost blinking.

[Salita Kadir]

It's inspired by the paper motion without movement.

[Emily Kwong]

The edges of her are being adjusted through computer programming.

[Salita Kadir]

We've taken this 2D illusion into the third dimension by first estimating the depth of the image and then calculating the speed per pixel for a dynamic, lifelike effect. And there you have it, a mesmerizing blend of art and science.

[Emily Kwong]

It's so cool. What did you think when you first saw this submission?

[Susana Martinez Conde]

Well, I thought that it was a beautiful illusion. I still do. And I think that it brings together so well the science and the art, because you're not just watching the implementation of a brain principle, of a perception principle, but you're actually watching art. And I think that that's what makes illusion so captivating in a way.

[Emily Kwong]

Why study illusions at all as scientists? What is the value in studying them and for these early career scientists to take time to do it?

[Susana Martinez Conde]

The definition of an illusion is a disconnect between objective reality and subjective perception. Because of this disconnect in illusions between perception and reality, we can, as scientists, go in and analyze the neurons and the brain circuits that support activity, neural neural activity that matches perception, and those could be part of the neural basis of consciousness. Whereas if you have neurons and circuits that have activity that matches reality rather than perception, those would not be part of the circuit that underlies consciousness.

[Emily Kwong]

The contest will presumably continue next year, so people can submit from anywhere in the world?

[Susana Martinez Conde]

Yes, absolutely. Anybody can participate. You can be an illusion creator and you can participate as a contestant. And you can also participate by voting for the best illusions.

[Emily Kwong]

Susana Martinez Conde, it was so good to talk to you. Thank you so much for coming on Short Wave.

[Susana Martinez Conde]

Thank you for having me.

[Emily Kwong]

Shortwavers. I like to think of every episode of our show as a combination of science and magic, just like an illusion. So if you never want to miss another one, subscribe, follow like whatever app you're listening to. And that way you'll never miss out. This episode was Produced by Burleigh McCoy. It was edited by our showrunner, Rebecca Ray Ramirez, and fact checked by Tyler Jones. The audio engineer was Maggie Luthar. Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Emily Kwong. Thank you for listening to Short Wave from npr.

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