ArticleslgStudy

physics

Troxler's fading

Troxler's fading is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Troxler's fading rather than just read about it. In short: Troxler's fading, also called Troxler fading or the Troxler effect, is an optical illusion affecting visual perception. When one fixates on a particular point for even a short period of time, an unchanging stimulus away from the fixation point will fade away and disappear.

Troxler's fading — main illustration
Troxler's fading — illustration

Key takeaways

  • Troxler's fading belongs to physics; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Troxler's fading to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Troxler's fading from memory before moving on to harder problems.

Reference excerpt

Troxler's fading, also called Troxler fading or the Troxler effect, is an optical illusion affecting visual perception. When one fixates on a particular point for even a short period of time, an unchanging stimulus away from the fixation point will fade away and disappear. Research suggests that at least some portion of the perceptual phenomena associated with Troxler's fading occurs in the brain.

Discovery Troxler's fading was first identified by Swiss physician Ignaz Paul Vital Troxler in 1804, who was practicing in Vienna at the time.

Process

Neural adaptation Troxler's fading has been attributed to the adaptation of neurons vital for perceiving stimuli in the visual system. It is part of the general principle in sensory systems that unvarying stimuli soon disappear from our awareness. For example, if a small piece of paper is dropped on the inside of one's forearm, it is felt for a short period of time. Soon, however, the sensation fades away. This is because the tactile neurons have adapted and start to ignore the unimportant stimulus. But if one jiggles one's arm up and down, giving varying stimulation, one will continue to feel the paper.

Visual parallels

A similar "sensory fading", or filling-in, can be seen of a fixated stimulus when its retinal image is made stationary on the retina (a stabilized retinal image). Stabilization can be done in at least three ways.

First, one can mount a tiny projector on a contact lens. The projector shines an image into the eye. As the eye moves, the contact lens moves with it, so the image is always projected onto the same part of the retina; Second, one can monitor eye movements and move the stimulus to cancel the eye movements; Third, one can induce an afterimage, usually by an intense, brief flash, such as when one is photographed using a photographic flash (a form of stabilized retinal image that most people have experienced). This causes an image to be bleached onto the retina by the strong response of the rods and cones. In all these cases, the stimulus fades away after a short time and disappears. The Troxler effect is enhanced if the stimulus is small, is of low contrast (or "equiluminant"), or is blurred. The effect is enhanced the further the stimulus is away from the fixation point.

Explanation of effect Troxler's fading can occur without any extraordinary stabilization of the retinal image in peripheral vision because the neurons in the visual system beyond the rods and cones have large receptive fields. This means that the small, involuntary eye movements made when fixating on something fail to move the stimulus onto a new cell's receptive field, in effect giving unvarying stimulation. Further experimentation this century by Hsieh and Tse showed that at least some portion of the perceptual fading occurred in the brain, not in the eyes.

See also Cognitive science Lilac chaser – An illusion that involves Troxler fading Bloody Mary - one of the most well known examples of this effect

References

External links Troxler project: a research project on Troxler's fading Archived 2017-04-06 at the Wayback Machine

Illustrations

Troxler's fading: In this example, the spots in the "lilac chaser" illusion fade away after several seconds when the black cross is stared at long enough. This leaves a grey background and the cross. Some viewers may notice that the moving space has faded into a moving blue-green spot, possibly with a short trail following it. Furthermore, moving one's eyes away from the image after a period of time may result in a brief, strong afterimage of a circle of green spots.
In this example, the spots in the "lilac chaser" illusion fade away after several seconds when the black cross is stared at long enough. This leaves a grey background and the cross. Some viewers may notice that the moving space has faded into a moving blue-green spot, possibly with a short trail following it. Furthermore, moving one's eyes away from the image after a period of time may result in a brief, strong afterimage of a circle of green spots.
Troxler's fading: The neural adaptation effect of Troxler's fading can be experienced by looking at the cross from a short distance without moving the eyes. After a few seconds, the colors seem to vanish. [Click on image to enlarge]
The neural adaptation effect of Troxler's fading can be experienced by looking at the cross from a short distance without moving the eyes. After a few seconds, the colors seem to vanish. [Click on image to enlarge]

Worked examples

Example 1 — a first encounter with Troxler's fading

Start with the simplest possible case. Write down what Troxler's fading claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Troxler's fading before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Troxler's fading ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Troxler's fading

In research
Troxler's fading appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Troxler's fading in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Troxler's fading is common in secondary-school and first-year university syllabi. It links to neighbouring topics Optical illusions, Visual perception, so understanding it makes those chapters shorter.
In everyday life
Look for Troxler's fading outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Troxler's fading” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Troxler's fading in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Troxler's fading means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Troxler's fading out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Troxler's fading in simple terms?

Troxler's fading, also called Troxler fading or the Troxler effect, is an optical illusion affecting visual perception. When one fixates on a particular point for even a short period of time, an unchanging stimulus away from the fixation point will fade away and disappear.

Why does Troxler's fading matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Troxler's fading?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Troxler's fading.

Tags

  • Optical illusions
  • Visual perception

Keep exploring