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Parapsychologists such as Dean Radin and Daryl 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 consistently indistinguishable from null results.
 Historical contextThe 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 and began using the ganzfeld technique as a more efficient way to achieve a state of sensory deprivation in which it is hypothesised that psi can work. Since the first full experiment was published by 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 procedureIn a typical ganzfeld experiment, a "receiver" is placed 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.
 Analysis of results
 Early experimentsBetween 1974 and 1982, 42 ganzfeld experiments were performed. In 1982, Charles Honorton presented a paper at the annual convention of the Parapsychological Association that 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.
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 that 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.
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.
 Post-Joint CommuniquéIn 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 entertainers (magicians whose specialty is simulating psi effects) examined Honorton's experimental arrangements, and pronounced them to provide excellent security against deception by subjects. 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.
The PRL trials continued until September 1989. Of the 354 trials, 122 produced direct hits. This 34% hit rate was statistically similar to the 37% hit rate of the 1985 meta-analysis. These experiments were statistically significant with a z score of 3.89, which corresponds to a 1 in 45,000 probability of obtaining a hit rate of at least 34% by chance (mean chance expectation is 25%).
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.
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). These experiments 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.
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
 Contemporary researchThe ganzfeld procedure has continued to be refined over the years. In its current incarnation, an automated computer system is used to select and display the targets ("digital autoganzfeld"). This overcomes many of the shortcomings of earlier experimental setups, such as randomization and experimenter blindness with respect to the targets 
In 2010, Lance Storm, Patrizio Tressoldi, and Lorenzo Di Risio analyzed 29 ganzfeld studies from 1997 to 2008. Of the 1,498 trials, 483 produced hits, corresponding to a hit rate of 32.2%. This hit rate is statistically significant with p < .001. Participants selected for personality traits and personal characteristics thought to be psi-conducive were found to perform significantly better than unselected participants in the ganzfeld condition.
 Psi-conducive variablesParapsychologists have investigated certain personality traits and characteristics as potential psi-conducive variables, suggesting that most researchers share the view that these variables play an important role in ESP performance. These factors are thought to be positively correlated with increased scores in ganzfeld experiments, as compared to unselected participants. Traits and characteristics of subjects thought to increase the chance of obtaining a successful hit rate in a psi experiment include:
- Positive belief in psi; ESP 
- Prior psi experiences 
- Practicing a mental discipline such as meditation 
- Creativity 
- Artistic ability 
- Emotional closeness with the sender 
 CriticismThere are several common criticisms of some or all of the ganzfeld experiments:
Isolation — Richard 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. However, Dean Radin argues that ganzfeld studies that did use soundproof rooms had a number of "hits" similar to those that did not.
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.
The psi assumption — The assumption that any statistical deviation from chance is evidence for telepathy is highly controversial. 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 might be fallacious.
 ControversyIn 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.
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 and prejudiced. His co-workers also responded, saying that any deviation from protocol was the result of “random errors” rather than any concerted attempt at fraud. Carl Sargent 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 in that organization was allowed to lapse.It now appeared that on one session — number 9 — the following events had taken place.
- Sargent did the randomization when he should not have.
- A 'B' went missing from the drawer during the session, instead of afterwards.
- Sargent came into the judging and 'pushed' the subject towards 'B'.
- An error of addition was made in favour of 'B' and 'B' was chosen.
- 'B' was the target and the session a direct hit.
 See also
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