Zener cards were developed and designed by Karl Zener, a Swiss Psychologist, and his associate J.B Rhine, at Duke University during the 1930′s, to test an individual’s psychic abilities or ESP (Extra Sensory Perception).
Zener cards can test many types of psychic abilities including the ability to perceive objects or events that already exist or have occurred, but are not known to you (clairvoyance); your ability to see the future (precognition); and the ability to transfer thoughts or feelings via a medium other then the 5 senses (telepathy).
A deck of Zener Cards consists of 25 cards made up of 5 subsets of identical cards. The pictures on the 5 cards consisted of a cross, waved lines, a hollow circle, a hollow star, and a hollow square.
Zener cards were originally made out of a flimsy material. This material was later determined to be biased due to its translucence which allowed individuals to see the shapes through the cards. So, subsequent decks utilized a thicker card stock to eliminate the bias and lend credibility to the statistical data.