physics

Shepard tables

Shepard tables 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 Shepard tables rather than just read about it. In short: Shepard tables (also known as the Shepard tabletop illusion) are an optical illusion first published in 1990 as "Turning the Tables," by Stanford psychologist Roger N. Shepard in his book Mind Sights, a collection of illusions that he had created.

Key takeaways

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

Reference excerpt

Shepard tables (also known as the Shepard tabletop illusion) are an optical illusion first published in 1990 as "Turning the Tables," by Stanford psychologist Roger N. Shepard in his book Mind Sights, a collection of illusions that he had created. It is one of the most powerful optical illusions, typically creating length miscalculations of 20–25%.

To quote A Dictionary of Psychology, the Shepard table illusion makes "a pair of identical parallelograms representing the tops of two tables appear radically different" because our eyes decode them according to rules for three-dimensional objects. This illusion is based on a drawing of two parallelograms, identical aside from a rotation of 90 degrees. When the parallelograms are presented as tabletops, however, we see them as objects in three-dimensional space. One "table" seems long and narrow, with its longer dimension receding into the distance. The other "table" looks almost square, because we interpret its shorter dimension as foreshortening. The MIT Encyclopedia of the Cognitive Sciences explains the illusion as an effect of "size and shape constancy [which] subjectively expand[s] the near-far dimension along the line of sight." It classifies Shepard tables as an example of a geometrical illusion, in the category of an "illusion of size." According to Shepard, "any knowledge or understanding of the illusion we may gain at the intellectual level remains virtually powerless to diminish the magnitude of the illusion." Children diagnosed with autism spectrum disorder are less susceptible to the Shepard table illusion than typically developing children but are equally susceptible to the Ebbinghaus illusion. Shepard had described an earlier, less-powerful version of the illusion in 1981 as the "parallelogram illusion" (Perceptual Organization, pp. 297–9). The illusion can also be constructed using identical trapezoids rather than identical parallelograms. A variant of the Shepard tabletop illusion was named "Best Illusion of the Year" for 2009. Christopher W. Tyler, among others, has done scholarly research on the illusion.

References

External links Animation of the illusion. Opticalillusion.net. More optical illusions by Roger Shepard

Illustrations

Worked examples

Example 1 — a first encounter with Shepard tables

Start with the simplest possible case. Write down what Shepard tables 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 Shepard tables 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 Shepard tables 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 Shepard tables

In research: Shepard tables 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 Shepard tables 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: Shepard tables is common in secondary-school and first-year university syllabi. It links to neighbouring topics Optical illusions, so understanding it makes those chapters shorter.
In everyday life: Look for Shepard tables 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.

Affiliate

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

How to study Shepard tables in 20 minutes

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

Frequently asked questions

What is Shepard tables in simple terms?

Why does Shepard tables 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 Shepard tables?

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 Shepard tables.