What are Zener Cards?

Zener Cards are eponymous ESP targets, created by psychologist Karl Zener in response to JB Rhine’s efforts to make ESP experiments easier to judge. They are comprised of five distinctive symbols: circle, cross, wavy lines, square and star.

Before Zener cards, studies tended to use regular playing cards, which apart from having a low likelihood of being guessed correctly (1/52 on a closed deck) and having inherent biases (people preferring face cards over numbers), have two types of information on them: number and suit. If the Seven-of-Spades was the target card and you guessed Seven-of-Clubs (which was the wrong card, but with the right number and also a ‘black’ symbol), were you half right?

In having a single characteristic, Zener cards simplified matters into simple hits and misses. The use of Zener cards is what is known as a forced-choice protocol, where participants know they can only choose from the five possible symbols. Zener cards are no longer used in parapsychological research.