A ganzfeld experiment (from the German for “entire field”) is a technique used in the field of parapsychology to test individuals for extrasensory perception (ESP). 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.
Consistent, independent replication of the ganzfeld experiment has not been achieved. Critics such as Susan Blackmore and Ray Hyman say the results are inconclusive and consistently indistinguishable from null results.
The ganzfeld was originally introduced into experimental psychology due to the experiments of the German psychologist Wolfgang Metzger (1899-1979) on the perception of a homogenous visual field. 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 he hypothesised that a concept referred to by some as "psi" can work. Honorton believed that by reducing the ordinary sensory input, "psi" conductive states may be enhanced and psi-mediated information may be transmitted.
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.
In 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
Between 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.
The ganzfeld studies examined by Hyman and Honorton had methodological problems that were well documented. Honorton reported only 36% of the studies used duplicate target sets of pictures to avoid handling cues. Hyman discovered flaws in all of the 42 ganzfeld experiments and to access each experiment, he devised a set of 12 categories of flaws. Six of these concerned statistical defects, the other six covered procedural flaws such as inadequate documentation, randomization and security as well as possibilities of sensory leakage. Over half of the studies failed to safeguard against sensory leakage and of all of the studies contained at least one of the 12 flaws. Because of the flaws, Honorton agreed with Hyman the 42 ganzfeld studies could not support the claim for the existence of psi.
In 1986, Hyman and Honorton published A Joint Communiqué which agreed on the methodological problems and on ways to fix them. The result of the collaboration was a process called the autoganzfeld study. A computer-automated control, where randomization and the other methodological problems identified were eliminated. Hyman and Honorton agreed that 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.
In 1983 Honorton had started a series of autoganzfeld experiments at his Psychophysical Research Laboratories (PRL). These studies were specifically designed to avoid the same potential problems as those identified in the 1986 joint communiqué issued by Hyman and Honorton. In 1990, Honorton et al. published the results of 11 autoganzfeld experiments they claimed met the standards specified by Hyman and Honorton (1986).
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%).
Hyman analyzed these experiments and wrote they met the standards of the 1986 joint communiqué "with the possible exception of proper randomization of targets during the sending and the judging procedures as well as the possibility of inadequate safeguards against sensory leakage." Daryl Bem and Honorton (1994) reviewed the experimental arrangements of the autoganzfeld experiments, and pronounced them to provide excellent security against deception by subjects and sensory cues. Hyman disagreed with Bem and Honorton as he had discovered some interesting patterns in the data that implied visual cues may have taken place in the experiments:
The most suspicious pattern was the fact that the hit rate for a given target increased with the frequency of occurrence of that target in the experiment. The hit rate for the targets that occurred only once was right at the chance expectation of 25%. For targets that appeared twice the hit rate crept up to 28%. For those that occurred three times it was 38%, and for those targets that occurred six or more times, the hit rate was 52%. Each time a videotape is played its quality can degrade. It is plausible then, that when a frequently used clip is the target for a given session, it may be physically distinguishable from the other three decoy clips that are presented to the subject for judging. Surprisingly, the parapsychological community has not taken this finding seriously. They still include the autoganzfeld series in their meta-analyses and treat it as convincing evidence for the reality of psi.
Julie Milton and Richard Wiseman (1999) published a critique of Bem and Honorton and a review of new ganzfeld studies. They discovered that Bem and Honorton had counted the results of some studies as being statistically significant when they actually were not significant. This error led Bem and Honorton to conclude overall, that a psi effect was operating in the ganzfeld. Milton and Wiseman (1999) carried out a meta-analysis of ganzfeld experiments in other laboratories. They found no psi effect, the results showed no effect greater than chance from a database of 30 experiments and a non-significant Stouffer Z of 0.70.
Other meta-analyses were criticized 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.
Lance Storm and Suitbert Ertel (2001) published a meta-analysis of 79 studies published between 1974 and 1996 and concluded the positive statistically significant overall outcome indicates a psi effect. In response, Milton and Wiseman (2001) wrote the meta-analysis of Storm and Ertel was not an accurate quantitative summary of ganzfeld research as they had included early studies which had been widely recognized as having methodological problems which make it impossible to interpret the results as evidence of a psi effect.
Another 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 a Stouffer Z of 2.59.
The 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 a review, Ray Hyman (2007) wrote that parapsychologists agree they have no positive theory of psi as it is negatively defined as any effect that cannot be currently explained in terms of chance or normal causes and this is a fallacy as it encourages parapsychologists into using any peculiarity in the data as a characteristic of psi.
Until parapsychologists can provide a positive way to indicate the presence of psi, the different effect sizes that occur in experiments are just as likely to result from many different things rather than one thing called psi. Indeed given the obvious instability and elusiveness of the findings, the best guess might very well be that we are dealing with a variety of Murphy's Law rather than a revolutionary anomaly called psi.—Ray Hyman, Evaluating Parapsychological Claims, 2007
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. Hyman (2010) published a rebuttal to Storm et al.
Bem and Honorton (1994) investigated certain personality traits and characteristics as potential psi-conducive variables which they suggested play an important role in ESP performance. According to parapsychologists 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 
While there are a number of reasons that researchers avoid special participants and sample only normal populations, these factors are important considerations in future replications of ganzfeld experiment, and may be useful in predicting the outcome of these studies.
There 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 could have heard it, and later given involuntary cues to the receiver during the selection process. It could even have been possible that the receiver themselves could hear the video. 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 is fallacious.
Terence Hines (2003) has written the ganzfeld studies cannot be said to provide evidence for psi as the alleged evidence disappears as the tightness of experimental controls is increased. As research progresses variables in science become clearer as more studies are published that describe under what specific condition the particular effect can be demonstrated. This is in opposition to the ganzfeld studies. According to Hines "After all this time, there is no clear way to obtain results showing any psychic phenomenon reliably. By far the most reasonable conclusion is that such effects do not now and never have existed."
Parapsychologists have admitted it is impossible to eliminate the possibility of non-paranormal causes in the ganzfeld experiment. There is no independent method to indicate the presence or absence of psi. In 2013, Brian Dunning reviewed the flaws of the ganzfeld studies and came to the conclusion the technique has failed as evidence for psi and interest in ganzfeld has declined.
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 in 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.
This article, along with further criticisms of Sargent's work from Adrian Parker and Nils Wiklund remained unpublished until 1987 but all were well known in parapsychological circles. Sargent wrote a rebuttal to these criticisms (also not published until 1987)  in which he did not deny what Blackmore had observed, but argued that 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 of that organization was allowed to lapse.
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