Zener cards n.
A deck of 25 cards used in research into extra-sensory perception. On the face of each card is printed one of five symbols (circle, cross, square, star, or wavy lines); therefore, the chance probability of a hit is 1/5 for an individual card, and the number of hits expected on the basis of chance alone for the complete pack is five. Also called ESP cards. [Named after the US psychologist Karl E(dward) Zener (1903–64) who devised them at Duke University in 1930 and objected in vain to their being named after him]