The Lilac Chaser Illusion

The lilac chaser is a type of visual illusion that was first discovered by vision expert Jeremy Hinton in 2005. In order to see the illusion, open and view the lilac chaser illusion in a new window. Stare at the black center cross for a minimum of 30 seconds and see what happens. Like other visual illusions, the lilac chaser illusion is a fun and interesting way to observe how the brain and perception work.

What Is the Lilac Chaser Illusion?

In the lilac chaser illusion, the viewer sees a series of lilac-colored blurry dots arranged in a circle around a focal point. As the viewer stares at the focal point, they may experience a few different visuals.

At first, there will appear to be a space running around the circle of lilac discs. After about 10 to 20 seconds, the viewer will then see a green disc moving around the circle instead of the space. With longer observation, the lilac discs will disappear altogether and the viewer will only see the green disc moving around in a circle.

According to its inventor Jeremy Hinton, "the illusion illustrates Troxler fading, complementary colors, negative after-effects, and is capable of showing colors outside the display gamut." In order to understand how the illusion works, it is important to understand these perceptual phenomena.

Apparent Movement

The lilac chaser illusion is an example of what is known as apparent movement or beta movement. When you see something in one spot and then again in a slightly different spot, you tend to perceive movement.

You can probably think of multiple examples of this in real life. Motion pictures and neon signs operate based upon this principle.

How Neon Signs "Move"

A progressively flashing neon sign is able to create the illusion of movement simply by altering the timing and spacing that the lights are flashed.

Negative Afterimage

When a color is presented in the visual field for an extended period of time, an afterimage results. An afterimage involves continuing to see colors briefly even after a stimulus is no longer present. You generally don't notice afterimages because you move your eyes frequently enough that these afterimages rarely occur in day-to-day experience.

In some cases, you see the colors exactly as they were in the original image, which is known as a positive afterimage. In other cases, you see the opposing colors of the original image, which is known as a negative afterimage. In the lilac chaser illusion, you see a green (negative) afterimage in place of the lilac discs.

Fading

Troxler fading occurs when blurry objects that are located in the periphery of your visual field disappear while you have your eyes fixated on a certain spot. This effect is more pronounced with lower contrast images.

Movement

After you fixate on the center cross for about 30 seconds or so and the lilac discs have disappeared, it seems as if the green disc is now flying around the circle by itself. This can be explained by a Gestalt effect known as the phi phenomenon. The sequential movement of the retinal afterimage (aka, the green disc) causes the illusion of movement.

Variations

While the illusion is usually observed by looking at the black cross at the center, it isn't necessary to look at it to see the effect. As long as you hold your gaze on any point, you will notice the effect. You can also try:

  • Following the gap between the circles with your eyes
  • Staring at the image for several minutes, then looking away at a blank wall or sheet of paper
  • Moving away from the screen once the single green disc appears while keeping your eyes fixed on the center cross
  • Closing your right eye, then moving close to the screen

Trying these variations can demonstrate some of the limits of the visual perception system.

Illusions such as the lilac chaser illusion help researchers investigate how the brain perceives and interprets visual information.

A Word From Verywell

First created in 2005, the lilac chaser illusion has become a popular optical illusion widely shared online. The effect is interesting because it illustrates a number of aspects of visual perception, including the effects of negative afterimages and the phi phenomenon.

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  1. Bach M. Lilac chaser. Updated June 6, 2021.

  2. American Psychological Association. Afterimage. APA Dictionary of Psychology.

  3. Bachy R, Zaidi Q. Troxler fading, eye movements, and retinal ganglion cell propertiesIperception. 2014;5(7):611-612. doi:10.1068/i0679sas

  4. American Psychological Association. Phi phenomenon. APA Dictionary of Psychology.