Zener Card

Definition: Zener Cards are also known simply as "ESP cards." When Chicago botanist Joseph Banks Rhine began his experiments at the Harvard psychology department on psychic phenomena, he was assisted by Karl E. Zener, a colleague in that department. The two performed "card guessing" experiments in which a researcher would pull a card off of a deck and look at it while the subject would attempt to guess what was on the card - correct guesses which were significantly more than what would be predicted by chance was assumed to indicate the presence of telepathic or clairvoyant powers. 

In order to simplify procedures, Zener came up with five cards, each with distinct symbols on them: a cross, a star, a circle, a square and three wavy lines. These cards eventually became very popular by those studying psychic phenomena and have been used in experiments around the world. When they were first introduced, however, it was shown that the symbols on them could be read quite readily from the backs (with enough light) and even from the sides. This likely contributed to the high scores achieved by subjects in the early experiments.