The cards were designed by Psychologist Karl Zener in the early 1930's, they were used to help conduct experiments for extra sensory perception, Karl conducted many experiments along side his collegue parasychologist J B Rhine.

There are 25 cards in a pack and five of each design which are, a hollow circle, a greek cross, three vertical wavy lines, a hollow square and a hollow five pointed star.

In the experiment the pack of cards would be shuffled and the experimenter would pick out a card and the person (subject) would then try to guess which symbol it was, this would continue till all the cards had been used, the results would be recorded throughout the experiment as well as concluded afterwards the results. Different methods have been tried to keep the subject from seeing the cards or gaining anything from the experimenter including sitting in a different room. The average result for the experiment is a correct guess of 5 cards, but it is not unusal for a person with no psychic ability to only score 1 or 2 correct.