Extra-sensory perception (ESP) is the term that encompasses the phenomena of telepathy, clairvoyance, and precognition. These unusual perceptions are normally dismissed as paranormal nonsense by scientists who state there is and has never been measurable proof of their existence in the human mind. Not so for Karl Zener. A behavioural psychologist who taught at Princeton and Duke, he maintained a Pavlovian research centre in the United States during the 1930s, and along with his colleague Joseph Rhine, devised the card symbols that were used by Rhine in early ESP tests. Rhine called these cards “Zener cards.”

The Zener cards are a set of of cards similar to a deck of playing cards. Each deck contains five cards each of different symbols: a star, three wavy lines, a cross, a circle, and a square. To test a subject’s potential telepathic ability, the “sender” shuffles the set and chooses a card. The “receiver” then tries to identify the symbol on the chosen card by “reading” the sender’s mind. cards are shuffled (usually mechanically) and a designated sender turns the cards over one at a time to inspect the symbol while a receiver attempts to guess the symbol by reading the thoughts of the sender.

So… what symbol am I thinking of, Avocado?

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