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This is TED Health, a podcast from the TED Audio Collective, and I'm your host, Dr. Shoshana Ungerleiter. You know when you stare at a bright light and then you see those colorful shapes dancing across your vision afterwards? Well, you've just experienced an afterthought.
image. But what's really happening in your eyes and in your brain when you see things that aren't technically there? And what does that mean for your overall health? This TED-Ed lesson takes us on a fascinating journey into the science of vision. Exploring what these after images, optical illusions, and even a little pressure on your eyeballs can reveal about how our brains process the world. Our eyes do a lot more than just see. They help shape how we think, how we feel, and even
So before you rub your eyes or stare at the sun, please don't do that. Get ready for a talk that may just change the way you see, well, everything. And now, your TED-Ed lesson of the day. In the late 1600s, Isaac Newton conducted a series of experiments that broke the two most fundamental rules of eye safety. In one, he stared at the sky.
Newton was hoping to better understand the lights and colors that sometimes appear when your eyes are closed. If you've ever sat around an evening campfire or, unlike Newton, unintentionally glanced at the sun, you may have noticed illuminated patterns briefly dance along your vision before fading into darkness. So how do these visual illusions, known as afterimages,
Inside the retina, specialized cells called photoreceptors take in light and turn it into a signal the brain can understand. Photoreceptors contain thousands of molecules called photopigments. which are sensitive to particular colors. When a light photon strikes a pigment Part of the photopigment structure, known as chromophore, absorbs the energy by temporarily altering its molecular structure in a process called bleaching. This reconfiguration induces a cascade of chemical reactions.
that route an electrical pulse to the brain. brain assembles the signals from approximately 200 million photoreceptor cells, you see an image. So how does this lead to an afterimage? Scientists aren't quite sure, but a leading theory suggests that photoreceptors may be to blame. Looking at something bright causes many pigments in a photoreceptor to bleach. state photopigments can't absorb light well and need to regenerate.
However, it's believed that photoreceptor cells momentarily continue to fire and to send signals to the brain, transforming the blazing campfire to a bright pattern as you close your eyes. This is known as a positive afterimage. Positive afterimages normally fade within a few seconds and, under certain conditions, can be replaced by what is known as a negative afterimage.
The original colors appear to be swapped for their approximate complement. Blue with yellow, red with cyan, green with magenta. If you fixate on a bright image of a green flower on a yellow background, then glance at a white screen or close your eyes, you will see a negative afterimage of a magenta flower on a blue background.
Scientists are still working to understand the origins of negative afterimages. And there are multiple theories. Some evidence suggests the source lies in the layers of neuronal cells in the retina, called ganglion cells. Another theory suggests the source lies, again, in the photoreceptors. The idea is that certain cells are activated if one color, such as green, is viewed. while other cells that are normally activated by viewing red green's complement are then left deactivated.
But if you stare at a green image for an extended period of time, it's thought that while the activated green cells become fatigued, the red cells are still sensitive to input. As a result, when you look away or close your eyes The opposing red cells are momentarily more active than the tired green cells, creating the perception of a color that is close to the original color's complement. But scientists still don't know for sure.
And yet another puzzling visual illusion involves no light or staring at all. Simply rubbing, or like Newton, inadvisably stabbing behind your eye, can generate the brief appearance of lights and colors. Newton hypothesized that the colorful circles of light were caused by the physical bending of his retina. Today, some scientists believe that pressure phosphenes are indeed the result of distortion.
That rubbing or poking your eyes physically stretches neurons, bending the photoreceptors out of shape and causing them to fire. But again, the science of phosphenes is far from settled. And there are other ways they can form. For example, during procedures where magnetic pulses are sent into specific parts of the brain, some people, including those with certain types of blindness, traveling where few others have gone before often describe seeing similar effects when
And that's it for today's episode. Thank you so much for listening. TED Health is part of the TED Audio Collective. This episode was produced by me, Dr. Shoshana Ungerleiter, and Jess Shane. Edited by Alejandra Salazar and fact-checked by Vanessa Garcia-Woodworth. Special thanks to Maria Lages. If you enjoyed today's episode, rate and review the show on your favorite platform. It helps other people to find us.
And I'd really love to hear your feedback. Send me a message on Instagram at ShoshanaMD. Support for this episode comes from the University of Illinois Geese College of Business MBA program known as the IMBA, which provides the environment and resources that empower you to make your mark and put your purpose into practice. Kara Kasner, a graduate of the program, can attend.
Hi, my name is Kara Kasner. I am a 2023 graduate of the IMBA program at the University of Illinois Geese College of Business. I am currently the director of digital marketing at Kendall Corporation, which is a provider of senior living and aging services. So when I started, I... The biggest change was when I found out I was pregnant and I knew I didn't want to stop the program. I wanted to keep going.
but I was able to take a summer off to have the baby and to spend time with the baby. And because the program is flexible, it really had no adverse effect on me at all. I was able to just pick it back up when I was ready to and finish. There's a network here that's really unmatched. It's huge. It's global and you're going to find someone in your field. You're going to find someone in your function. You're going to find people that have
commonalities with you, but you're also going to find so many people that aren't. I think that's really unique to Geese. I think you're going to get a high quality education. You're going to meet a lot of people and you're going to do that at a really affordable price. I think what surprised me the most is how quickly I was able to take what I learned and just take it right to work with me. I had been kind of reaping the benefits the whole way along.
really from that first class I took, I was able to exhibit that in my work. I definitely think that my team at work has noticed and has seen me bring these things to play. I got pulled into more things than I would have if I hadn't done this program. I'm glad I went this route. I think it was the best choice for me. And I think it's a good choice for many people that are in similar situations to me as well.
No matter what your career path, Geese College of Business Online MBA has a curriculum that gives you the right mix of practical and leadership learning to meet your specific career goals. and be more competitive on the job market. Learn more at gisonline.illinois.edu. Since when did pride in your country become prejudice?
We speak your mind. Easter's on its way, so make your way to Aldi, where you'll find everything on your shopping list, including a delicious and tender whole leg of lamb on sale now. Our exquisite, specially selected hot cross buns. Hand finished, packed with dried fruit and good housekeeping institute taste approved 2025 no less. So you'll be hot and cross if you miss them. Get your old ears now. Aldi!