A ganzfeld experiment is a technique used in the field of parapsychology to test individuals for extra sensory perception. It uses homogeneous and unpatterned sensory stimulation to produce an effect similar to sensory deprivation. The deprivation of patterned sensory input is said to be conducive to inwardly generated impressions. The technique was devised by Wolfgang Metzger in the 1930s as part of his investigation into the gestalt theory.
The ganzfeld experiments are among the most recent in parapsychology for testing the existence of and affecting factors of telepathy, which is defined in parapsychology as the paranormal acquisition of information concerning the thoughts, feelings or activity of another person. In the early 1970s, Charles Honorton had been investigating ESP and dreams at the Maimonides Medical Center but became frustrated at the cumbersome nature of the process.
Since the first full experiment was published by Charles Honorton and Sharon Harper in the Journal of the American Society for Psychical Research in 1974, the ganzfeld has remained a mainstay of parapsychological research.
In a typical ganzfeld experiment, a receiver is left in a room relaxing in a comfortable chair with halved ping pong balls over the eyes, having a red light shone on them. The receiver also wears a set of headphones through which white or pink noise is played. The receiver is in this state of mild sensory deprivation for half an hour. During this time a sender observes a randomly chosen target and tries to mentally send this information to the receiver. The receiver speaks out loud during the thirty minutes, describing what he or she can see. This is recorded by the experimenter either by recording onto tape or by taking notes, and is used to help the receiver during the judging procedure.
In the judging procedure, the receiver is taken out of the ganzfeld state and given a set of possible targets, from which they must decide which one most resembled the images they witnessed. Most commonly there are three decoys along with a copy of the target itself, giving an expected overall hit rate of 25% over several dozens of trials.
Between 1974 and 2004, 88 ganzfeld experiments were done, reporting 1,008 hits in 3,145 tests. In 1982, Charles Honorton presented a paper at the annual convention of the Parapsychological Association which summarized the results of the ganzfeld experiments up to that date, and concluded that they represented sufficient evidence to demonstrate the existence of psi. Ray Hyman, a skeptical psychologist, disagreed. The two men later independently analyzed the same studies, and both presented analyses of them in 1985. Honorton thought that the data at that time indicated the existence of psi, and Hyman did not.
Parapsychologists such as Dean Radin and Daryl J. Bem say that ganzfeld experiments have yielded results that deviate from randomness to a significant degree, and that these results present some of the strongest quantifiable evidence for telepathy to date. Critics such as Susan Blackmore and Ray Hyman say that the results are inconclusive, and call for further study before such results can be scientifically accepted.