What are those colors you see when you rub your eyes? - Paul CJ Taylor

Summary

The video explores the intriguing phenomenon of afterimages and pressure phosphenes, inspired by Isaac Newton's daring experiments with light. Afterimages occur when photoreceptors in the retina become fatigued from prolonged exposure to bright colors, causing temporary color illusions when you look away. Positive afterimages fade quickly, while negative afterimages reveal complementary colors. Pressure phosphenes, on the other hand, arise from physical manipulation of the eyes, distorting neurons and generating flashes of light. This captivating investigation highlights ongoing scientific inquiries into the complexities of human vision and the mysterious interplay between light and perception.

Takeaways

• 🌞 In the late 1600s, Isaac Newton conducted experiments on eye safety, including staring at the sun and puncturing his eye with a needle.
• 👀 Afterimages are visual illusions that occur after looking at bright lights or patterns.
• 💡 Photoreceptors in the retina convert light into signals that the brain can interpret, using molecules called photopigments.
• ⚡ The process of bleaching occurs when light-photons alter the structure of photopigments, leading to electrical signals sent to the brain.
• 🌀 Positive afterimages appear when photoreceptors continue sending signals to the brain even after the initial stimulus is removed.
• 🔄 Negative afterimages occur when the original colors are replaced by their complementary colors after staring at a bright image.
• 🔬 Research is ongoing to understand the origins of negative afterimages, with multiple theories being explored.
• 👁️ Pressure phosphenes are visual effects caused by physical pressure on the eye, resulting in the perception of lights and colors.
• 🌌 Astronauts and people with certain types of blindness can experience flashes of light due to cosmic radiation or magnetic pulses in the brain.
• 🔍 The science of phosphenes and afterimages remains complex and is still being studied by scientists.

Q & A

What experiments did Isaac Newton conduct related to eye safety?

Isaac Newton conducted experiments where he stared directly at the sun and stuck a needle under his eyeball, both of which broke fundamental rules of eye safety.

What are afterimages and how do they form?

Afterimages are visual illusions that appear after looking at a bright light source. They form due to the photoreceptors in the retina, which take in light, leading to chemical reactions that send signals to the brain. When photoreceptors are overstimulated, they can continue to send signals even after the stimulus is removed, creating afterimages.

What is the role of photopigments in afterimages?

Photopigments in photoreceptors are sensitive to specific colors and undergo a process called bleaching when they absorb light. This process temporarily alters their structure and affects their ability to absorb light, contributing to the formation of afterimages.

What is the difference between positive and negative afterimages?

Positive afterimages occur when bright colors are viewed and can be seen briefly after looking away, while negative afterimages involve the original colors being swapped for their complementary colors, such as seeing magenta after looking at green.

How does the brain process signals from photoreceptors?

The brain assembles signals from approximately 200 million photoreceptor cells to create visual images based on the electrical pulses sent from these cells after exposure to light.

What is the scientific consensus on the causes of negative afterimages?

There is no clear consensus on the causes of negative afterimages. Theories range from the involvement of ganglion cells in the retina to deeper processing in the brain, and the possibility that certain photoreceptors become fatigued while others remain active.

What are pressure phosphenes?

Pressure phosphenes are visual sensations that occur when pressure is applied to the eye, such as rubbing or poking. They are caused by the physical distortion of the retina, leading to the firing of photoreceptors.

What did Newton hypothesize about the cause of pressure phosphenes?

Newton hypothesized that the colorful circles of light experienced as pressure phosphenes were caused by the physical bending of his retina.

What additional phenomena can lead to visual sensations similar to phosphenes?

Visual sensations similar to phosphenes can also occur during procedures involving magnetic pulses in the brain and are reported by some individuals, including those with certain types of blindness. Astronauts have also reported seeing such effects due to exposure to cosmic radiation.

Why is the science of phosphenes considered unsettled?

The science of phosphenes is considered unsettled because there are multiple theories about their origins and mechanisms, and ongoing research continues to explore these visual phenomena.