What are those colors you see when you rub your eyes? - Paul CJ Taylor
TED-Ed・2 minutes read
Isaac Newton's late 1600s experiments on eye safety led him to investigate afterimages, a visual phenomenon tied to the brain's processing of signals from around 200 million photoreceptor cells in the retina. The mechanisms behind different types of afterimages, including positive and negative, as well as pressure phosphenes caused by physical manipulation of the eyes, remain complex and under scientific inquiry.
Insights
- Isaac Newton's groundbreaking experiments in the late 1600s, which involved extreme methods like staring at the sun and inserting needles into his eye, were aimed at understanding afterimages—a visual effect caused by the brain's processing of signals from around 200 million photoreceptor cells in the retina. These experiments highlighted the delicate balance between curiosity and safety in scientific inquiry, as well as the complex mechanisms of how our eyes and brain interact with light.
- Afterimages are classified into positive, which briefly linger after viewing bright light, and negative, where original colors shift to their complementary hues. While positive afterimages fade quickly, negative afterimages involve more complex processes that are still being studied, suggesting that our understanding of color perception and visual processing in the brain is still evolving and may involve intricate interactions between retinal cells and brain functions.
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Recent questions
What are afterimages in vision?
Afterimages are visual phenomena that occur when a person sees a lingering image after looking away from a bright light source. This effect is primarily due to the way photoreceptors in the retina respond to light. When exposed to intense illumination, these photoreceptors absorb light and send signals to the brain, creating the perception of an image. Afterimages can be categorized into positive and negative types. Positive afterimages appear in the same colors as the original stimulus and fade quickly, while negative afterimages involve the perception of complementary colors, which can last a bit longer. Understanding afterimages provides insight into the complex workings of our visual system and how our brain processes light and color.
How do I improve my eyesight?
Improving eyesight can involve several strategies, including regular eye examinations, maintaining a healthy diet rich in vitamins A, C, and E, and engaging in eye exercises. It's also important to protect your eyes from excessive screen time by following the 20-20-20 rule, which suggests taking a break every 20 minutes to look at something 20 feet away for at least 20 seconds. Additionally, wearing sunglasses to shield your eyes from harmful UV rays and ensuring proper lighting while reading or working can help maintain eye health. If you have specific vision concerns, consulting an eye care professional for personalized advice and potential corrective measures is essential.
What causes visual illusions?
Visual illusions are caused by the brain's interpretation of visual information, which can sometimes lead to misperceptions of reality. These illusions occur when the brain processes sensory input in a way that does not accurately reflect the external environment. Factors contributing to visual illusions include the arrangement of objects, lighting conditions, and the context in which images are viewed. For example, afterimages, a type of visual illusion, arise from the overstimulation of photoreceptors in the retina, leading to lingering perceptions of light and color. Understanding the mechanisms behind visual illusions can reveal much about how our brains construct our visual experiences and the complexities of perception.
What are pressure phosphenes?
Pressure phosphenes are visual sensations that occur when pressure is applied to the eyes, such as when rubbing or poking them. This pressure can distort the retina, causing photoreceptors to fire and create the perception of light or patterns, even in the absence of actual light stimuli. Historically, Isaac Newton attributed these sensations to the physical bending of the retina, but modern theories suggest that they result from the stretching of neurons due to pressure. Pressure phosphenes illustrate the intricate relationship between physical stimuli and visual perception, highlighting how our sensory systems can be influenced by non-visual factors.
What is the role of photoreceptors?
Photoreceptors are specialized cells in the retina that play a crucial role in converting light into electrical signals, which are then transmitted to the brain to form visual images. There are two main types of photoreceptors: rods and cones. Rods are responsible for vision in low light conditions and are highly sensitive to light, while cones are responsible for color vision and function best in bright light. These cells contain photopigments that absorb light, leading to a process called bleaching, which triggers a cascade of biochemical reactions resulting in the generation of nerve impulses. The intricate functioning of photoreceptors is essential for our ability to perceive and interpret the visual world around us.
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Summary
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Newton's Eye Experiments and Visual Phenomena
- In the late 1600s, Isaac Newton conducted dangerous experiments on eye safety, including staring at the sun and inserting a needle under his eyeball, to explore the visual phenomena known as afterimages, which occur when illuminated patterns briefly appear in one’s vision after exposure to bright light. This phenomenon is linked to the function of photoreceptors in the retina, which contain photopigments that absorb light and undergo a process called bleaching, leading to the brain receiving signals from approximately 200 million photoreceptor cells to form images.
- Afterimages can be categorized into positive and negative types. Positive afterimages occur when photoreceptors continue to send signals to the brain after looking at a bright light, typically fading within a few seconds. Negative afterimages happen when the original colors are replaced by their complementary colors, such as seeing a magenta flower on a blue background after staring at a green flower on a yellow background. The mechanisms behind negative afterimages are still under investigation, with theories suggesting involvement of ganglion cells in the retina or deeper brain processing.
- Pressure phosphenes, another visual illusion, can occur without light exposure, such as when rubbing or poking the eyes, which may distort the retina and cause photoreceptors to fire. Newton believed these were due to physical bending of the retina, while current theories suggest that stretching neurons from pressure leads to this effect. Additionally, magnetic pulses in the brain and cosmic radiation exposure in astronauts can also induce similar visual experiences, indicating that the science behind phosphenes remains complex and not fully understood.
