A pack of twenty-five cards bearing simple symbols in groups of five of a kind: star, circle, square, cross, and waves, used in parapsychology in testing extrasensory faculty under laboratory conditions. The use of the Zener card pack dates from the work of J. B. Rhine in the Department of Psychology at Duke University, North Carolina, from 1927 onward, first reported in Rhine's Extrasensory Perception, published 1934 by the Boston Society for Psychic Research.
Prior to the work of Rhine, ordinary playing cards had been used in testing telepathy, notably by Margaret Verrall between 1890 and 1895. Significant tests were carried out in Britain by Ina Jephson and other members of the Society for Psychical Research beginning in 1924.
The Zener card pack was devised by Karl Zener (1903-1963) of the psychology faculty at Duke University as a means of avoiding preferences for individual playing cards during tests and in order to facilitate evaluation of test scores. Having concluded that parapsychology as pursued by Rhine was a threat to the psychology department, Zener later turned against Rhine and joined with some colleagues in an attempt to have him removed from his faculty position.
Two problems developed with the Zener cards. First, while they were designed to be more emotionally neutral than traditional playing cards, in fact, they used some highly charged emotional symbols, such as the star, a prominent symbol in many religions. Second, in the early printings, the ink bled through and the symbol was clearly visible on the back of the card. This later problem was immediately corrected when discovered.
Berger, Arthur S., and Joyce Berger. The Encyclopedia of Parapsychology and Psychical Research. New York: Paragon House, 1991.
Jephson, Ina. "Evidence for Clairvoyance in Card-Guessing: A Report on Some Recent Experiments." Proceedings of the Society for Psychical Research 38: 223-271, and 39: 375-414.
Jephson, Ina, S. G. Soal, and Theodore Besterman. "Report on a Series of Experiments in Clairvoyance (conducted at a distance)." Proceedings of the Society for Psychical Research 39 (1928).
Sanger, C. P. "Analysis of Mrs. Verrall's Card Experiments." Proceedings of the Society for Psychical Research 2, no. 28 (1895).