Zener cards

Zener cards are cards used to conduct experiments for extrasensory perception (ESP) or clairvoyance.

Perceptual psychologist Karl Zener (1903–1964) originally used images before designing the cards in the early 1930s. These were used for experiments conducted with his colleague, parapsychologist J. B. Rhine (1895–1980).

They bear the symbols circle, square, wavy lines, cross, and star. There are five of each type of card in a pack of 25.