In 1937, a person could go to a newsstand and pick up a pack of cards for 10 cents. But these were no ordinary playing cards: They were Zener cards, developed to test one's friends for the presence of extrasensory perception, or ESP.
Duke University perceptual psychologist Karl Zener, PhD, (1903-64) designed the cards in the 1930s for experimental ESP research with fellow Duke psychologist J.B. Rhine, PhD (1895-1980).
After hearing Scottish author Sir Arthur Conan Doyle give a lecture attesting to the scientific proof that one could communicate with the dead, Rhine became interested in examining ESP, and he set up a laboratory to test subjects for psychic abilities.
One of his experiments involved the cards, which came 25 to a pack. Inside were five cards each of five different designs--a circle, cross, wave, square and star--chosen because each had one more line than the other. The back side of the card had a blue background with a design and a Duke building. Although Rhine did much of the research, he had Zener design the cards since Zener was a perceptual psychologist.
In his experiments, Rhine would hold up the card with the back side forward and ask the subject to tell him which design was on the front of the card.
He conducted tests in myriad conditions seeking to remove outside forces that would clue subjects into what was on the card. For example, to remove shuffling errors, he used a machine to shuffle cards. To eliminate the chance of card counting, he did not tell subjects if they were correct or not on a guess. To remove physical or facial cues, he put subject and experimenter in different rooms. In one test, he put a high performing subject and experimenter 250 yards apart.
All of these tests were done in different conditions to strengthen the scientific validity of the results. In 1934, Rhine published the book "Extra Sensory Perception" summarizing his years of research with the cards. He believed the data were supportive enough of ESP to warrant continued investigation.
Rhine's decades of research inspired the growth of parapsychology. But today, ESP remains at the fringe of scientific inquiry with 96 percent of scientists in the National Academy of Sciences skeptical of the concept.
Regardless, Rhine infused an area of folk wisdom with a scientific quality that was previously absent--and it's hard to criticize the man for applying scientific rigor to the field.
Nick Joyce works at and Dr. David Baker directs the Archives of the History of American Psychology at the University of Akron in Ohio.
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