Zener cards were developed in the 1930s by perceptual psychologist Karl Zener to conduct rigorous, scientific testing for extrasensory perception and clairvoyance at Duke University.

A closer look

Zener cards were developed in the 1930s by perceptual psychologist Karl Zener to conduct rigorous, scientific testing for extrasensory perception and clairvoyance at Duke University. The deck consists of twenty-five cards featuring five simple symbols like a hollow circle, a plus sign, three vertical wavy lines, a hollow square, and a hollow five-pointed star. Researchers spent decades having people stare at the back of these cards, desperately hoping someone could guess the symbol using their mind power to prove that telepathy was a legitimate scientific phenomenon. Despite years of intense, painfully boring research, the only thing they conclusively proved is that human beings are incredibly skilled at unconsciously cheating and reading subtle reflections in the glasses of the person holding the deck