Stare at a brightly colored image for a short time, then look at a blank white surface and observe a “ghost” image that appears in complementary colors. This activity demonstrates how cone cells adapt and how the opponent process in vision creates negative and positive afterimages.

1. Prepare a high-contrast, colored image with a small fixation dot at the center, or display a colored shape on a screen.
2. Dim room lights slightly to reduce glare, then have participants sit an arm’s length from the image.
3. Instruct participants to fixate the center dot without blinking for about 20–30 seconds while keeping head and eyes as still as possible.
4. Quickly replace the image with a blank white screen or have participants shift gaze to a nearby white wall or sheet of paper.
5. Ask them to describe the afterimage they see, noting that the colors appear as complements of the original.
6. Repeat using a grayscale version to show that bright flashes can produce brief positive afterimages in the same shades as the original.
7. Discuss why the effect fades with time and why it returns if the original stimulus is viewed again.

Afterimage/Negative Photo Illusion (See a negative in color) - Kids Fun Science:

The Colour After-Image Illusion - Fascinating Psychology:

📄 How afterimages play tricks on your eyes - All About Vision: https://www.allaboutvision.com/resources/human-interest/afterimage/

• Use colored squares of red, green, blue, and yellow to compare which complements appear most clearly.
• Try the “lilac chaser” style ring of pink dots with a central fixation cross to observe a moving green afterimage and the Troxler effect.
• Present an inverted-color portrait and have participants report the more natural-looking afterimage when they look at a white surface.
• Compare durations: show a bright image very briefly to highlight positive afterimages vs longer viewing for negative afterimages.
• Test different backgrounds (white vs black vs mid-gray) to see how contrast changes afterimage visibility.

• Do not use very bright light sources, camera flashes, or sunlight as stimuli; use standard screens or printed images.
• Limit each fixation period to about 30 seconds and provide breaks to reduce eye strain.
• Screen participants for photosensitive epilepsy or migraine sensitivity; allow anyone to opt out without pressure.
• Avoid excessive room darkness to prevent trips or falls during station changes.

• Why are negative afterimages seen in complementary colors? (Cone cells sensitive to the viewed color become adapted, so activity in the opponent channel shifts toward the complementary color when you look at a neutral background.)
• What is the difference between negative and positive afterimages? (Negative afterimages appear in complementary colors and last longer; positive afterimages briefly match the original colors and fade quickly.)
• Which retinal cells are responsible for color afterimages and what do their roles differ from rods? (Cones mediate color and adapt during sustained stimulation; rods are more sensitive in low light and contribute little to color.)
• How do the Troxler effect and phi phenomenon relate to afterimages? (Troxler makes unchanging peripheral stimuli fade during steady fixation; phi makes sequences of static images appear as motion, which positive afterimages can help smooth.)
• Why might an intense afterimage be a reason to see an eye doctor? (Persistent or frequent afterimages can be part of palinopsia, which may indicate an underlying condition that needs evaluation.)