Colours Design

Afterimage Effects

What do the snow and a camera flash have in common? Afterimage, a phenomenon of visual perception can make an image last a little longer after the image is gone.

Afterimage are optical illusions of images that continue to appear after the exposure of the image ended. This can occur with either a prolonged exposure of one colour or brief exposure to a very bright image surrounded by a darker area. This could be a positive or negative image left behind.

Have you ever experienced afterimage?

Afterimage can occur commonly in two ways by brief exposure to a very bright stimulus particularly when the surrounding conditions are much darker. Like a flash of light from a camera. The second way would be prolonged exposure to one colour. When people stare at a particular colour for a long period the eyes become tired and fatigued. The mechanics of afterimage are not well understood since scientists are still studying the effects. Since it’s still being studied, this post will be brief.

Positive Afterimage

Positive afterimage happens when the colours are retained. The colours would look like to original image. This could be because of retinal inertia when the original image simulates nerve impulses in the eyes. These impulses continue when you close your eyes or looking away from the image. Just not exposed to the image anymore. Some cells on the retina keep transmitting signals to the brain for a little while. The cells take some time to respond to the image; once excited it takes more time to stop. Afterimage can last as long as 500 milliseconds which in comparison the eye can see as little as 13 milliseconds.

“The job of the eyes is not only to get the information into the brain, but to allow the brain to think about it rapidly enough to know what you should look at next. So in general we’re calibrating our eyes so they move around just as often as possible consistent with understanding what we’re seeing,”

Mary Potter, an MIT professor of brain and cognitive sciences and senior author of Attention, Perception, and Psychophysics

Many philosophers perceive positive afterimages has pathological calling it physiological afterimages. They are perceived as a normal and common phenomenon.

Stare at the rubber duckies for 10 seconds then blink. If you still see rubber duckies then that’s positive afterimage.

An example of positive afterimage

You’re at a party, like in a bar or banquet hall. The place is very dark with some light around it. Someone wants to take your picture but they left the flash on. It’s very bright and you continue seeing the light after the photo was taken until your eyes calm down. That’s a positive afterimage.

Negative Afterimage

Negative afterimage happens when the colours are in reverse. We would be seeing the opposite colours that are there. This happens when our eye’s rods and cones adapt to overstimulation and lose sensitivity. These often occurs in darkness or a lack of light. When someone is in a dark area staring at a bright object, for example, a red object then if the person’s glaze is brought to a bright place the person will view the object has a green afterimage. After staring at an object for an extended period, the red rods and cones in the eyes become exhausted for a short period which makes the green very active.

These two images will emerge into one by using afterimage in the video.

Just stare at the bird in the video without moving your eye. For 20 seconds concentrate on the bird. The bird will appear to be in the cage.

The printed version of the bird in a cage is called a thaumatrope which is a two slide animation that emerges by pulling on string. Both sides have different images that compliment an overall illustration. The two images flicker at a speed that the start to look like one image. This was a popular optical illusion in the 19th century that was featured in Sleepy Hollow (1999).

A theory to explain afterimage being opponent-process theory. This theory mostly explains how negative afterimage works. The opponent-process theory is a psychological and neurological model for a wide range of behaviour studies even colour vision. First, we need four colours to help define colour like blue, red, yellow and green. The theory implies that people see colours in three opposing systems; blue versus yellow, red versus green and black versus white. Colour is perceived at two colours at a time but only one of the opposing colours. This is part of the reason why we can see yellowish-greens and reddish-yellows but not reddish-green or yellowish-blue.

An example of negative afterimage

When I was younger I attended swimming classes. I when I in the pool, I was in a cyan-blue environment for at least an hour. When I left the pool area and went to the balcony of the pool area with the walls painted white, I only saw red glares in my sight. The cells in my eyes, particularly the blue-green cells in my eyes, were strained from over stimuli.

Therefore, afterimage was a real thing that happened to me.

This is the woman in positive view.

Resources:

Afterimages – Washington University

Very Well Mind – Why Do People Experience Afterimages as an Optical Illusion?

The Illusions Index – Positive Afterimages

The Illusions Index – Negative Afterimages

Healthline – Opponent Process Theory

MIT News – In the blink of an eye


Images courtesy of Unsplash and Under The Moonlight

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