What are Zener cards? The history of the ESP deck

Zener cards are the five-symbol cards (circle, cross, waves, square and star) made for ESP experiments at Duke University in the 1930s. The design is credited to psychologist Karl Zener, working with J. B. Rhine. The experiments did not hold up, but the cards became a mentalism classic that magicians still use today.

What are Zener cards?

A classic Zener deck has 25 cards with five symbols, five cards of each: a hollow circle, a plus sign or cross, three wavy lines, a hollow square and a five-pointed star. With five equal choices, a guess on any single card has a one-in-five chance of being right, so pure guessing averages about five hits in a run of 25.

That simple maths was the point. It made it easy to see whether someone was scoring better than chance.

Who made them, and why?

The deck is credited to Karl Zener (1903–1964), a perceptual psychologist at Duke University. He designed the cards in the 1930s for the ESP research of his Duke colleague J. B. Rhine (1895–1980).

Rhine had first tested people with ordinary playing cards, but people tend to favour certain cards, which muddied the results. Five plain symbols with no strong associations were meant to fix that.

How were the cards used in tests?

An experimenter took a card from a shuffled pack and the subject tried to name its symbol. Rhine moved from shuffling by hand to a shuffling machine.

In 1934 Rhine published Extra-Sensory Perception, summarising his card research. The idea caught on with the public: by 1937, packs of ESP cards were sold at newsstands for 10 cents.

What did the critics say?

Many scientists were critical of the method. Critics found ways the symbol could leak to the guesser, from printing that showed through to the back of a card to faint marks and other cues from the experimenter. Later attempts to repeat Rhine’s results under tighter controls did not hold up consistently.

Even Zener later distanced himself from Rhine’s ESP work. Today, mainstream science does not accept ESP, and the cards are mostly used to teach about chance, and to entertain.

If you enjoy stories where magic meets the supernatural, our post on magician John Nevil Maskelyne is a good next read.

Why do magicians use ESP cards?

The same things that made Zener cards good for the lab make them good for a show. The symbols are bold and simple, so an audience can see them from across a room, and with only five choices a spectator can remember theirs easily. Many routines use the cards to stage a “test” of the audience’s intuition, then turn the tables with a prediction.

The Bicycle Jumbo ESP set suggests a handy memory aid: the circle has one line, the cross two, the waves three, the square four and the star five.

As always with mentalism, the honest approach is to present it as entertainment. Our beginner’s guide to mentalism covers how to do that, and the pendulum trick is a great companion piece that needs no cards at all.

What helps you take it further?

• Bicycle ESP Deck Red (55 cards). A poker-size deck printed by the USPCC on Rider Back cards: 50 ESP cards (ten of each symbol), three gaff cards and a QR card with instructions for seven effects.
• Bicycle Jumbo ESP 50 Cards. A jumbo set of 50 (ten of each symbol), made for parlour and stage, in red or blue backs. Instructions are not included.
• Wooden ESP Cards by Joker Magic. Five birch ESP cards, one of each symbol, in a black velvet bag, with an online video explaining eleven routines. The backs are not marked and can be examined.

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