Zener cards are cards used to conduct experiments for extrasensory perception (ESP) or clairvoyance. Perceptual psychologist Karl Zener (1903–1964) designed the cards in the early 1930s for experiments conducted with his colleague, parapsychologist J. B. Rhine (1895–1980).
The Zener cards are a deck of twenty-five cards, five of each symbol. The five symbols are a hollow circle, a plus sign, three vertical wavy lines, a hollow square, and a hollow five-pointed star.
In a test for ESP, the experimenter picks up a card in a shuffled pack, observes the symbol, and records the answer of the person being tested, who would guess which of the five designs is on the card. The experimenter continues until all the cards in the pack are tested.