Zener cards

ESP-Cards_2011_by-Lauren-Nurse

 

Zener cards are cards used to conduct experiments for extra-sensory perception (ESP), most often 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).

(Wikipedia – Zener cards)