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Participant of a Ganzfeld telepathy experiment.

A ganzfeld experiment (from the German for “entire field”) is a technique used in the field of parapsychology to test individuals for extra-sensory perception (ESP). It uses homogeneous and unpatterned sensory stimulation to produce an effect similar to sensory deprivation.[1] The deprivation of patterned sensory input is said to be conducive to inwardly-generated impressions.[2] The technique was devised by Wolfgang Metzger in the 1930s as part of his investigation into the gestalt theory.[3]

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.[4] 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.[5][6][7]

Historical context

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.[8] 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.[How to reference and link to summary or text]

In searching for a more efficient way to achieve a state of sensory deprivation in which it is hypothesised that psi can work,[9] Honorton decided upon the ganzfeld protocol.

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.

Experimental procedure

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 (static) 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 (who is blind to the target) 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.[10]

Analysis of results

Between 1974 and 2004, 88 ganzfeld experiments were done, reporting 1,008 hits in 3,145 tests.[11] 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 meta-analyses of them in 1985. Honorton thought that the data at that time indicated the existence of psi, and Hyman did not.[12][13]

Hyman's criticisms were that the ganzfeld papers did not describe optimal protocols, nor were they always accompanied by the appropriate statistical analysis. He presented in his paper a factor analysis which he said demonstrated a link between success and three flaws, namely: Flaws in randomization for choice of target; flaws in randomization in judging procedure; and insufficient documentation. Honorton asked a statistician, David Saunders, to look at Hyman's factor analysis and he concluded that the number of experiments was too small to complete a factor analysis. Additionally, Hyman had chosen his three flaws from a list of nine, and there are 84 ways to select three elements from nine, so Hyman had not corrected for multiple analysis.[14]

In 1986, Hyman and Honorton published A Joint Communiqué, in which they agreed that though the results of the ganzfeld experiments were not due to chance or selective reporting, replication of the studies was necessary before final conclusions could be drawn. They also agreed that more stringent standards were necessary for ganzfeld experiments, and they jointly specified what those standards should be.[15]

In 1983 Honorton had started a series of autoganzfeld experiments at his Psychophysical Research Laboratories. These studies were specifically designed to avoid the same potential problems as those identified in the 1986 joint communiqué issued by Hyman and Honorton. Ford Kross and Daryl Bem, both professional mentalist magicians (magicians whose specialty is simulating psi effects) examined Honorton's experimental arrangements, and pronounced them to provide excellent security against deception by subjects.[16] In addition to randomization consistent with the specifications of the communiqué, and computer control of the main elements of each test, these autoganzfeld experiments isolated the receiver in a sound-proof steel-walled and electromagnetically shielded room.[17]

The PRL trials continued till September 1989. Of the 354 trials, 122 produced direct hits. This is a 34% hit rate, and is similar statistically to the 37% hit rate of the 1985 meta-analysis (25% is expected by chance). The 34% hit rate is statistically significant with a z score of 3.89, meaning that there is a 1 in 45,000 chance that a hit rate of at least 34% is observed in the experiment when the true hit probability would really be 25%.[18][17]

Concerning these results, Hyman wrote that the final verdict of whether psi can be demonstrated in the ganzfeld awaited the results of future experiments conducted by other independent investigators.

To see if other, post-Joint Communiqué experiments had been as successful as the PRL trials, Julie Milton and Richard Wiseman carried out a meta-analysis of ganzfeld experiments carried out in other laboratories. They found no psi effect, with a database of 30 experiments and a non-significant Stouffer Z of 0.70.[19]

This meta-analysis was criticised for including all ganzfeld experiments, regardless of the methods being used. Some parapsychologists considered that certain researchers had used protocols that were not part of the standard ganzfeld set up, such as targets consisting of music (traditional ganzfeld experiments use visual targets).[20] It was these experiments which did not return significant results. A second meta-analysis was conducted by Daryl Bem, John Palmer, and Richard Broughton in which the experiments were sorted according to how closely they adhered to a pre-existing description of the ganzfeld procedure. Additionally, ten experiments that had been published in the time since Milton and Wiseman's deadline were introduced. Now the results were significant again with Stouffer Z of 2.59.[21]

In a 1995 paper discussing some of the challenges, deficiencies and achievements of modern laboratory parapsychology Ray Hyman said,

Obviously, I do not believe that the contemporary findings of parapsychology, [...] justify concluding that anomalous mental phenomena have been proven. [...] [A]cceptable evidence for the presence of anomalous cognition must be based on a positive theory that tells us when psi should and should not be present. Until we have such a theory, the claim that anomalous cognition has been demonstrated is empty.[...] I want to state that I believe that the SAIC experiments as well as the contemporary ganzfeld experiments display methodological and statistical sophistication well above previous parapsychological research. Despite better controls and careful use of statistical inference, the investigators seem to be getting significant results that do not appear to derive from the more obvious flaws of previous research.

Ray Hyman, The Journal of Parapsychology, December 1995[22]


There are several common criticisms of some or all of the Ganzfeld experiments:

IsolationRichard Wiseman and others argue that not all of the studies used soundproof rooms, so it is possible that when videos were playing, the experimenter (or even the receiver) could have heard it, and later given involuntary cues to the receiver during the selection process.[23] However, Dean Radin argues that ganzfeld studies which did use soundproof rooms had a number of "hits" similar to those which did not.[4][17]

Randomization — When subjects are asked to choose from a variety of selections, there is an inherent bias to choose the first selection they are shown. If the order in which they are shown the selections is randomized each time, this bias will be averaged out. The randomization procedures used in the experiment have been criticized for not randomizing satisfactorily.[24]

The psi assumption — The assumption that any statistical deviation from chance is evidence for telepathy is highly controversial, and often compared to the God of the gaps argument. Strictly speaking, a deviation from chance is only evidence that either this was a rare, statistically unlikely occurrence that happened by chance, or something was causing a deviation from chance. Flaws in the experimental design are a common cause of this, and so the assumption that it must be telepathy is fallacious. This does not rule out, however, that it could be telepathy.[25]


In 1979, Susan Blackmore visited the laboratories of Carl Sargent in Cambridge. She noticed a number of irregularities in the procedure and wrote about them for the Journal of the Society for Psychical Research.

It now appeared that on one session — number 9 — the following events had taken place.

  1. Sargent did the randomization when he should not have.
  2. A 'B' went missing from the drawer during the session, instead of afterwards.
  3. Sargent came into the judging and 'pushed' the subject towards 'B'.
  4. An error of addition was made in favour of 'B' and 'B' was chosen.
  5. 'B' was the target and the session a direct hit.[26]

This article, along with further criticisms of Sargent's work from Adrian Parker and Nils Wiklund remained unpublished until 1987 but were well known in parapsychological circles. Sargent wrote a rebuttal to these criticisms (also not published until 1987) in which he did not deny that what Blackmore saw occurred, but her conclusions based on those observations were wrong. He stopped working in parapsychology after this and did not respond "in a timely fashion" when the Council of the Parapsychological Association asked for his data and so his membership of said organization was allowed to lapse.[27]

See also


  1. Radin 1997, p. 70–80
  2. Parapsychological Association website, Glossary of Key Words Frequently Used in Parapsychology. URL accessed on 2006-03-01.
  3. Metzger, W (1930). Optische Untersuchungen am Ganzfeld: II. Zur Phanomenologie des homogenen Ganzfelds. Psychologische Forschung (13): 6–29.
  4. 4.0 4.1 Radin 1997
  5. (1987). The Elusive Open Mind: Ten Years of Negative Research in Parapsychology. The Skeptical Inquirer (11): 244–255.
  6. Daryl J. Bem (1994). Response to Hyman. Psychological Bulletin Vol. 115 (No. 1): 25–27.
  7. The Evidence for Psychic Functioning: Claims vs. Reality
  8. Parapsychological Association Glossary of Parapsychological terms. URL accessed on 2006-12-19.
  9. Honorton & Harper (1974). Psi-mediated imagery and ideation in an experimental procedure for regulating perceptual input. Journal of the American Society for Psychical Research (68): 156–168.
  10. Palmer, J. (2003). ESP in the Ganzfeld. Journal of Consciousness Studies 10 (no. 6–7).
  11. Dean I. Radin, Simon & Schuster (2006). Entangled Minds: Extrasensory Experiences in a Quantum Reality, Paraview Pocket Books.
  12. Ray Hyman (1985). The Ganzfeld Psi Experiments: A Critical Appraisal. Journal of Parapsychology (49).
  13. Charles Honorton (1985). Meta-Analysis of Psi Ganzfeld Research: A Response to Hyman. Journal of Parapsychology (49).
  14. Saunders (1985). On Hyman's Factor Analysis. Journal of Parapsychology (49).
  15. Hyman, Honorton (1986). A Joint Communique. Journal of Parapsychology (50).
  16. 1979 survey quoted in Daryl J. Bem and Charles Honorton (1994). Does Psi Exist? Replicable Evidence for an Anomalous Process of Information Transfer. Psychological Bulletin Vol. 115 (No. 1): 4–18.
  17. 17.0 17.1 17.2 Radin 1997, p. 77–89
  18. Honorton, Berger, Varvoglis, Quant, Derr, Schechter, Ferrari (1990). Psi Communication in the Ganzfeld. Journal of Parapsychology (54).
  19. Milton, Wiseman (1999). Does Psi Exist? Lack of Replication of an Anomalous Process of Information Transfer. Psychological Bulletin vol. 125 (no. 4): 387–391.
  20. Schmeidler, Edge (December 1999). Should Ganzfeld Research Continue To Be Crucial In The Search For A Replicable Psi Effect? Part ii. Journal of Parapsychology.
  21. Bem, Palmer, Broughton (2001). Updating the Ganzfeld Database: A Victim of Its Own Success. Journal of Parapsychology (65).
  22. Ray Hyman (December 1995). Evaluation of Program on Anomalous Mental Phenomena. The Journal of Parapsychology.
  23. Wiseman, R., Smith, M,. Kornrot, D.. Exploring possible sender-to-experimenter acoustic leakage in the PRL autoganzfeld experiments. Journal of Parapsychology.
  24. Hyman, Ray (1994). Anomaly or Artifact? Comments on Bem and Honorton. Psychological Bulletin 115 (1): 19–24.
  25. Carroll, Robert Todd (2005). The Skeptic's Dictionary: Psi Assumption. URL accessed on 2006-06-23.
  26. Blackmore (1987). A Report of a Visit to Carl Sargent's Laborator. Journal of the Society for Psychical Research.
  27. John Beloff (1997). Parapsychology: A Concise History, Palgrave MacMillan.


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