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{{Short description|Pseudoscientific test for extrasensory perception (ESP)}}

[[Image:Ganzfeld.jpg|frame|right|Participant of a [[Ganzfeld]] [[telepathy]] experiment.]]

{{For|the perceptual phenomenon when viewing a uniform stimulation field|Ganzfeld effect}}

[[File:Ganzfeld.jpg|frame|right|Participant in a ganzfeld experiment]]

A '''ganzfeld experiment''' (from the [[German language|German]] words for "entire" and "field") is an assessment used by [[parapsychology|parapsychologists]] that they contend can test for [[extrasensory perception]] (ESP) or [[telepathy]]. In these experiments, a "sender" attempts to mentally transmit an image to a "receiver" who is in a state of [[sensory deprivation]]. The receiver is normally asked to choose between a limited number of options for what the transmission was supposed to be and parapsychologists who propose that such telepathy is possible argue that rates of success above the expectation from [[randomness]] are evidence for ESP. Consistent, independent replication of ganzfeld experiments [[Replication crisis|has not been achieved]], and, in spite of strenuous arguments by parapsychologists to the contrary, there is no validated evidence accepted by the wider [[scientific community]] for the existence of any parapsychological phenomena. Ongoing parapsychology research using ganzfeld experiments has been criticized by independent reviewers as having the hallmarks of [[pseudoscience]].{{efn|name="pseudoscience"|Pseudoscience<ref>{{cite book | last=Frazier | first=Kendrick | author-link=Kendrick Frazier | title=The Hundredth monkey and other paradigms of the paranormal: a Skeptical inquirer collection | publisher=Prometheus Books | publication-place=Buffalo, NY | year=1991 | isbn=978-0879756550 | oclc=22909893 | pages=143–148}}</ref><ref>{{cite periodical |author-link=Ray Hyman |first=Ray |last=Hyman |year=1996 |url=http://www.csicop.org/si/show/evidence_for_psychic_functioning_claims_vs._reality/ |title=The Evidence for Psychic Functioning: Claims vs. Reality |magazine=The Skeptical Inquirer |pages=24–26 |access-date=November 4, 2013}}</ref><ref>{{cite book | last=Smith | first=J.C. | title=Pseudoscience and Extraordinary Claims of the Paranormal: A Critical Thinker's Toolkit | publisher=Wiley-Blackwell | year=2009 | isbn=978-1444358940 | url=https://books.google.com/books?id=sJgONrua8IkC | access-date=November 1, 2013}}</ref><ref>{{cite book |last=Rathus |first=Spencer |year=2011 |title=Psychology: Concepts and Connections |publisher=Cengage Learning |page=143 |isbn=978-1111344856}}</ref><ref name="Marks 2000">{{cite book |author-link1=David Marks (psychologist)|last1=Marks |first1=David |last2=Kammann |first2=Richard |year=2000 |title=The Psychology of the Psychic |title-link=The Psychology of the Psychic |publisher=Prometheus Books |pages=97–106 |isbn=1573927988}}</ref>}}

In the field of [[parapsychology]], a '''ganzfeld experiment''' (From the German for “entire field”) is a technique used to test individuals for [[extra-sensory perception]] (ESP). It uses homogeneous and un-patterned sensory stimulation to produce an effect similar to [[sensory deprivation]].<ref name="ConsciousUniverse"> ''The Conscious Universe: The Scientific Truth of Psychic Phenomena'' by Dean I. Radin Harper Edge, ISBN 0-06-251502-0</ref> (Radin 1997:70-80) The deprivation of patterned sensory input is said to be conducive to inwardly-generated impressions.<ref>http://parapsych.org/glossary_a_d.html Parapsychological Association website, Glossary of Key Words Frequently Used in Parapsychology, Retrieved January 3, 2006</ref> The technique was devised by [[Wolfgang Metzger]] in the [[1930s]] as part of his investigation into the [[Gestalt psychology|gestalt]] theory.<ref>Metzger, W. (1930). Optische Untersuchungen am Ganzfeld: II. Zur Phanomenologie des homogenen Ganzfelds. Psychologische Forschung, 13, 6-29.</ref>

Many ganzfeld experiments have yielded results that deviate from [[randomness]] to a [[statistical significance|significant]] degree,<ref>http://www.surveysystem.com/signif.htm ''Statistical Significance'' Definition of what is considered significant and "highly" significant, Creative Research Systems, Retrieved January 1, 2007</ref> and [[parapsychology|parapsychologists]] say that these results present some of the strongest quantifiable evidence for telepathy to date.<ref name="ConsciousUniverse"> ''The Conscious Universe: The Scientific Truth of Psychic Phenomena'' by Dean I. Radin Harper Edge, ISBN 0-06-251502-0</ref> Critics, however, say that the results are inconclusive at best.

==Historical context==

The [[ganzfeld effect]] was originally introduced into [[experimental psychology]] due to the experiments of the German psychologist [[Wolfgang Metzger]] (1899–1979) who demonstrated that subjects who were presented with a homogeneous visual field would experience perceptual distortions that could rise to the level of [[hallucination]]s.<ref name="Tyson2011">{{cite book | last1=Tyson | first1=Philip J. | last2=Jones | first2=Dai | last3=Elcock | first3=Jonathan | title=Psychology in social context: issues and debates | publisher=Wiley-Blackwell | publication-place=Chichester, West Sussex, UK/Malden, MA | year=2011 | isbn=978-1405168236 | oclc=683247699 | pages=199–200}}</ref> In the early 1970s, [[Charles Honorton]] at the [[Maimonides Medical Center]] was trying to follow in the footsteps of psychical researchers such as [[Joseph Banks Rhine]] who had coined the term "ESP" to elevate the discourse around [[paranormal]] claims. Honorton focused on what he thought was the connection between ESP and [[dream]]s and began exposing his research subjects to the same sort of [[sensory deprivation]] that is used in demonstrations of the ganzfeld effect, hypothesizing that it was under such conditions that "[[Psi (parapsychology)|psi]]" (a catch-all term used in [[parapsychology]] to denote anomalous psychic abilities) might work.<ref>{{cite journal | title=Psi-mediated imagery and ideation in an experimental procedure for regulating perceptual input | author=Honorton & Harper | journal=Journal of the American Society for Psychical Research | year=1974 | issue=68 | pages=156–168}}</ref> Honorton believed that by reducing the ordinary [[Sensory processing|sensory input]], "psi-conductive states" would be enhanced and "psi-mediated information" could be more effectively transmitted.<ref name="Tyson2011"/>

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.<ref>http://parapsych.org/glossary_s_z.html#t Parapsychological Association Glossary of Parapsychological terms, Retrieved Dec 19, 2006</ref> In the early [[1970s]], [[Charles Honorton]] had been investigating ESP and dreams at the [[Maimonides Medical Centre]] but became frustrated at the cumbersome nature of the process.{{Fact|date=February 2007}}

In searching for a more efficient way to achieve a state of sensory deprivation in which it is hypothesised that psi can work <ref>''Psi-mediated imagery and ideation in an experimental procedure for regulating perceptual input'' Honorton & Harper, Journal of the American Society for Psychical Research, 1974, 68, p156-68</ref> 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, thesuch "ganzfeld hasexperiments" have remained a mainstay of parapsychological research.

==Experimental procedure==

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 noise|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 30 minutes, describing what they can "see". The experimenter, who knows nothing of the chosen target, records these comments either on audiotape or through written notes.

Once time expires, the receiver is taken out of the Ganzfeld state and shown a set of possible targets, from which they select one which most resembles the images they witnessed. The receiver may refer to the notes/recordings made by the experimenter as needed. Most commonly there are three decoys along with the target, giving an expected rate of 25%, by chance, over several dozens of trials.<ref>{{cite journal | title=ESP in the Ganzfeld | author=Palmer, John | journal=Journal of Consciousness Studies | volume=10 | issue= 6–7 | year=2003}}</ref>

In a typical ganzfeld experiment, the 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 the 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/she can see. This mentation 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.

Some parapsychologists who accept the existence of psi have proposed that certain [[Trait theory|personality traits]] can enhance ESP performance.<ref name="BemHonorton1994">{{cite journal |last=Bem |first=Daryl J. |author2=Honorton, Charles |year=1994 |title=Does psi exist? Replicable evidence for an anomalous process of information transfer |url=http://www.dbem.ws/Does%20Psi%20Exist%3F.pdf |url-status=dead |journal=Psychological Bulletin |volume=115 |issue=1 |pages=4–18 |doi=10.1037/0033-2909.115.1.4 |archive-url=https://web.archive.org/web/20170317150522/http://www.dbem.ws/Does%20Psi%20Exist?.pdf |archive-date=2017-03-17 |access-date=2007-07-31}}</ref> Such parapsychologists have argued that certain characteristics in the participants could be selected for that would increase the scores of ganzfeld experiments.<ref name="StormEtAl2010" /> Such traits have included the following:

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.<ref>''ESP in the Ganzfeld,'' Palmer, J., Journal of Consciousness Studies, 10, no 6-7, 2003</ref>

* Positive belief in psi; ESP<ref name="Lawrence1993">{{cite journal |author=Lawrence, T.R. |year=1993 |title=Gathering in the sheep and goats: A meta-analysis of forced-choice sheep-goat ESP studies, 1947–1993 |journal=In Proceedings of the 36th Annual Convention of the Parapsychological Association |pages=75–86}}</ref>

* Prior psi experiences<ref name="BemHonorton1994" />

* Practicing a mental discipline such as meditation<ref name="BemEtAl2001" />

* Creativity<ref name="BemHonorton1994" />

* Artistic ability<ref name="BemHonorton1994" />

* Emotional closeness with the sender<ref name="Broughton1997">{{cite journal |author1=Broughton, R.S. |author2=Alexander, C.H. |year=1997 |title=AutoganzfeldII: An attempted replication of the PRL ganzfeld research |journal=Journal of Parapsychology |volume=61 |pages=209–226}}</ref>

Critics have pointed out that relying on selection criteria like this can introduce bias in the experimental design, and so generally discussion of any claimed effects has typically included only studies that sample normal populations rather than selecting for "special" participants (see below).<ref name="StormEtAl2010" />

==Analysis of results==

===Early experiments===

Between 1974 and 2004, 88 ganzfeld experiments were done, reporting 1,008 hits in 3,145 tests. <ref name="EntangledMinds">''Entangled Minds: Extrasensory Experiences in a Quantum Reality'' by Dean I. Radin, Simon & Schuster, Paraview Pocket Books , 2006 ISBN-13: 978-1416516774</ref> 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.<ref>''The Ganzfeld Psi Experiments: A Critical Appraisal'', Ray Hyman, Journal of Parapsychology 49, 1985</ref> <ref>''Meta-Analysis of Psi Ganzfeld Research: A Response to Hyman'', Charles Honorton, Journal of Parapsychology 49, 1985</ref>

Between 1974 and 1982, 42 ganzfeld experiments were performed by parapsychologists.<ref name=Honorton1985/><ref name="EntangledMinds">{{cite book | title=Entangled Minds: Extrasensory Experiences in a Quantum Reality | author=Radin, Dean| publisher=Paraview Pocket Books | year=2006 | isbn=978-1416516774}}</ref> In 1982, Charles Honorton presented a paper at the annual convention of the [[Parapsychological Association]] that presented his summary of the results of the ganzfeld experiments up to that date. Honorton concluded that the results represented sufficient evidence to demonstrate the existence of psi. [[Ray Hyman]], a psychologist and noted critic of parapsychology, disagreed. Hyman criticized the ganzfeld experiment papers for not describing optimal protocols, nor including the appropriate statistical analysis. He identified three significant flaws, namely, flaws in randomization for choice of target; flaws in randomization in judging procedure; and insufficient documentation. The two men later independently analyzed the same studies, and both presented meta-analyses of them in 1985.<ref name=Honorton1985>{{cite journal | title=Meta-Analysis of Psi Ganzfeld Research: A Response to Hyman | author=Honorton, Charles | journal=Journal of Parapsychology | issue=49 | year=1985}}</ref><ref>{{cite journal | title=The Ganzfeld Psi Experiments: A Critical Appraisal |author=Hyman, Ray | author-link=Ray Hyman | journal=Journal of Parapsychology | issue=49 | year=1985}}</ref>

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 randomisation for choice of target; flaws in randomisation 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.<ref>''On Hyman's Factor Analysis'', Saunders, Journal of Parapsychology 49, 1985</ref>

Hyman discovered flaws in all of the 42 ganzfeld experiments, and, to assess 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 randomization, inadequate security, possibilities of [[sensory leakage]], and inadequate [[documentation]]."<ref name="Hyman2007">{{cite book | last=Hyman | first=Ray | author-link=Ray Hyman |chapter=Evaluating parapsychological claims | editor-last=Sternberg | editor-first=Robert J. | editor-last2=Roediger | editor-first2=Henry L. | editor-last3=Halpern | editor-first3=Diane F. | title=Critical thinking in psychology | publisher=Cambridge University Press | publication-place=Cambridge; New York | year=2007 | isbn=978-0521608343 | oclc=69423179 | pages=216–231}}</ref> Honorton himself had reported that only 36% of the studies used duplicate target sets of pictures to avoid handling cues.<ref>{{cite journal |last1=Milton |first1=Julie |last2=Wiseman |first2=Richard |author-link2=Richard Wiseman |year=2002 |title=A response to Storm and Ertel (2002) |journal=The Journal of Parapsychology |volume=66 |pages=183–186}}</ref> Over half of the studies failed to safeguard against sensory leakage and all of the studies contained at least one of the 12 flaws. After considerable back-and-forth over the relevance and importance of the flaws, Honorton came to agree with Hyman the 42 ganzfeld experiments he had included in his 1982 [[meta-analysis]] could not in themselves support the claim for the existence of [[Psi (parapsychology)|psi]].<ref name="Hyman2007" />

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 exactly what those standards should be.<ref>''A Joint Communique'', Hyman, Honorton, Journal of Parapsychology 1986, issue 50</ref>

In 1986, Hyman and Honorton published ''A Joint Communiqué'' which agreed on the methodological problems and on ways to fix them. They suggested 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.<ref>{{cite journal |author1=Hyman, R. |author2=Honorton, C. |year=1986 |title=A joint communiqué: the psi ganzfeld controversy |journal=Journal of Parapsychology |volume=50 |issue=4 |pages=351–364}}</ref><ref>{{cite book | last=Neher | first=Andrew | title=The psychology of transcendence | publisher=Dover Publications | publication-place=New York | year=2011 | isbn=978-0-486-26167-6 | oclc=20562986 | page=307}}</ref>

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.<ref>http://www.dina.kvl.dk/~abraham/psy1.html 1979 survey quoted in ''Does Psi Exist? Replicable Evidence for an Anomalous Process of Information Transfer'' By Daryl J. Bem and Charles Honorton in the Psychological Bulletin 1994, Vol. 115, No. 1, 4-18</ref> 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.(Radin 1997: 77-89)

===Autoganzfeld===

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%.<ref> ''Psi Communication in the Ganzfeld'', Honorton, Berger, Varvoglis, Quant, Derr, Schechter, Ferrari, Journal of Parapsychology 54, 1990</ref>(Radin 1997: 77-89)

[[Image:Hyman LeeRoss DarylBem VictorBenassi.jpg|thumb|250px|right|Ray Hyman in 1983 with [[Lee Ross]], Daryl Bem and Victor Benassi]]

In 1982, Honorton had started a series of "autoganzfeld experiments", that is ganzfeld experiments controlled by a computer, at his Psychophysical Research Laboratories (PRL). The trials continued until September 1989 and in 1990 Honorton ''et al''. published the results of 11 autoganzfeld experiments they claimed met the standards specified by Hyman and Honorton (1986).<ref>{{cite journal |author1=Honorton, C. |author2=Berger, R.E. |author3=Varvoglis, M.P. |author4=Quant, M. |author5=Derr, P. |author6=Schechter, E.I. |author7=Ferrari, D.C. |year=1990 |title=Psi Communication in the Ganzfeld: Experiments with an Automated Testing System and a Comparison with a Meta-Analysis of Earlier Studies |journal=Journal of Parapsychology |volume=54 |issue=2 |pages=99–139}}</ref> In these experiments, 240 participants contributed 329 sessions.<ref name="BemHonorton1994"/>

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.

Hyman analyzed these experiments and wrote they met most, but not all of the "stringent standards" of the joint communiqué.<ref name="Hyman1994">{{cite journal | author = Hyman, Ray | author-link=Ray Hyman | year = 1994 | title = Anomaly or artifact? Comments on Bem and Honorton.| journal = Psychological Bulletin | volume = 115 | issue = 1| pages = 19–24 | doi=10.1037/0033-2909.115.1.19}}</ref> He expressed concerns with the randomization procedure, the reliability of which he was not able to confirm based on the data provided by Honorton's collaborator, [[Daryl Bem]]. Hyman further noted that although the overall hit rate of 32% (7% higher than the 25% expectation from randomness) was significant, the hit rate for static targets (pictures) was, in fact, consistent with random and therefore inconsistent with Honorton's previous claims of positive results from the ganzfeld experiments that were conducted prior to 1982. The significance of the results was due entirely to a new set of "dynamic targets" (videos) that participants were able to identify at a rate that was better than random.<ref name="Hyman1994"/> In the hit rates regarding these dynamic targets, however, patterns were evident that implied visual cues were leaked:

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.<ref>''Does Psi Exist? Lack of Replication of an Anomalous Process of Information Transfer'', Milton, Wiseman, Psychological Bulletin, 1999, vol 125, no 4, p 387-391</ref>

{{quote|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.<ref name="Hyman2007"/>}}

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).<ref>''Should Ganzfeld Research Continue To Be Crucial In The Search For A Replicable Psi Effect? Part ii'', Schmeidler, Edge, Journal of Parapsychology, Dec, 1999</ref> 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.<ref>''Updating the Ganzfeld Database: A Victim of Its Own Success'', Bem, Palmer, Broughton, Journal of Parapsychology, 65, 2001</ref>

Hyman wrote these studies were an improvement over their older counterparts, but were not a successful replication of the ganzfeld experiments, nor a confirmation of psi.<ref name="Hyman1994"/> He concluded the autoganzfeld experiments were flawed because they did not preclude the possibility of [[sensory leakage]].<ref name="Hyman2007"/>

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

<blockquote>

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.<ref>http://www.mceagle.com/remote-viewing/refs/science/air/hyman.html The Journal of Parapsychology, December, 1995, ''Evaluation of Program on Anomalous Mental Phenomena'' By Ray Hyman Retrieved January 5, 2007</ref>

</blockquote>

[[Richard Wiseman]] published a paper discussing a non-psi hypothesis based on possible sender to experimenter acoustic leakage in the autoganzfeld to account for the results.<ref name="Wiseman1996">{{cite journal |author1=Wiseman, R. |author2=Smith, M. |author3=Kornbrot, D. |year=1996 |title=Exploring possible sender-to-experimenter acoustic leakage in the PRL autoganzfeld experiments |journal=Journal of Parapsychology |volume=60 |pages=97–128 |issue=2 }}</ref><ref>{{cite book | last=Humphrey | first=Nicholas |author-link=Nicholas Humphrey | title=Soul searching: human nature and supernatural belief | publisher=Vintage | publication-place=London | year=1996 | isbn=978-0099273417 | oclc=36160610 | page=136 | quote=Richard Wiseman, a friend and former colleague of Honorton, has subsequently reanalysed the raw data trial by trial and shown that all the positive results can be attributed to those trials in which one or other of these sources of ‘sensory leakage’ was at least a possibility. In fact, in the relatively few trials (100 in all) where such leakage of information would not have been possible the receivers did no better than chance (26 per cent correct).}}</ref> [[David Marks (psychologist)|David Marks]] has written "Wiseman and his colleagues identified various different ways in which knowledge of the target could have been leaked to the experimenter. These included cues from the videocassette recorder and sounds from the sender who, of course, knew the target's identity... their conclusions provide little reassurance that sensory cueing of the experimenter was in any way substantially blocked."<ref name="Marks 2000"/>

== Criticism==

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-[[Statistical significance|significant]] [[Z-test|Stouffer Z]] of 0.70.<ref name=MiltonWiseman1999>{{cite journal | title=Does Psi Exist? Lack of Replication of an Anomalous Process of Information Transfer | first1=Julie | last1=Milton | first2=Richard | last2=Wiseman |author-link2=Richard Wiseman| journal=Psychological Bulletin | year=1999 | volume= 125 | issue= 4 | pages=387–391 | doi=10.1037/0033-2909.125.4.387 | pmid=10414223 | url=http://www.richardwiseman.com/resources/ganzmeta.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.richardwiseman.com/resources/ganzmeta.pdf |archive-date=2022-10-09 |url-status=live }}</ref>

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

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.<ref>{{cite journal | last1=Storm | first1=Lance | last2=Ertel | first2=Suitbert | title=Does psi exist? Comments on Milton and Wiseman's (1999) meta-analysis of Ganzfield research. | journal=Psychological Bulletin | volume=127 | issue=3 | year=2001 | doi=10.1037/0033-2909.127.3.424 | pages=424–433| pmid=11393304 }}</ref> 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.<ref name=MiltonWiseman2001>{{cite journal | title=Does psi exist? Reply to Storm and Ertel (2001) | first1=Julie | last1=Milton | first2=Richard | last2=Wiseman |author-link2= Richard Wiseman| journal=Psychological Bulletin | year=2001 | volume= 127 | issue= 3 | pages=434–438 | doi=10.1037/0033-2909.127.3.434 | citeseerx=10.1.1.377.1535 }}</ref>

''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.<ref>

{{cite web

| url = http://www.findarticles.com/p/articles/mi_m2320/is_n2_v60/ai_18960809

| title = Exploring possible sender-to-experimenter acoustic leakage in the PRL autoganzfeld experiments

| author = Wiseman, R., Smith, M,. Kornrot, D.

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| date = June 1996

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| publisher = Journal of Parapsychology

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| accessdate =

}}</ref> However, [[Dean Radin]] argues that ganzfeld studies which did use soundproof rooms had a number of "hits" similar to those which did not.<ref name="ConsciousUniverse"/> (Radin 1997: 77-89)

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 including some experiments that had been published in the time since Milton and Wiseman's deadline. They obtained results that were significant with a Stouffer Z of 2.59, but their detractors maintained their selection of studies for inclusion was problematic.<ref name=BemEtAl2001>{{cite journal|title=Updating the ganzfeld database: A victim of its own success? |vauthors=Bem DJ, Palmer J, Broughton RS |journal=Journal of Parapsychology |volume=65 |issue=3 |date=September 2001 |pages=207–218 |url=https://instruct1.cit.cornell.edu/courses/psych113/Bemetal.pdf |url-status=dead |archive-url=https://web.archive.org/web/20060914123724/http://instruct1.cit.cornell.edu/courses/psych113/Bemetal.pdf |archive-date=2006-09-14 }}</ref><ref>{{cite book | last1=Alcock | first1=James |author-link=James Alcock |last2=Burns |first2=Jean |last3=Freeman |first3=Anthony | title=Psi wars: getting to grips with the paranormal | publisher=Imprint Academic | publication-place=Exeter, UK/Charlottesville, VA | year=2003 | isbn=0907845487 | oclc=53963000 | page=59}}</ref>

''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 are shown the selections is randomized each time, this bias will be averaged out. However, this was often not done in the Ganzfeld experiments.<ref>

===Contemporary research===

The ganzfeld experiment 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 has the potential to overcome some of the shortcomings of earlier experimental setups, such as randomization and experimenter blindness with respect to the targets.<ref name=GouldingEtAl2004>{{cite journal | author1=Goulding, A. |author2=Westerlund, J. |author3=Parker, A. |author4=Wackermann, J. | year=2004 | title=The first Digital Autoganzfeld study using a real-time judging procedure | url=https://www.academia.edu/download/30657773/EJP_v19.pdf#page=69 |archive-url=https://ghostarchive.org/archive/20221009/https://www.academia.edu/download/30657773/EJP_v19.pdf#page=69 |archive-date=2022-10-09 |url-status=live | journal=European Journal of Parapsychology | volume=19 | pages=66–97}}{{dead link|date=July 2022|bot=medic}}{{cbignore|bot=medic}}</ref>

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 [[Statistical significance|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.<ref name=StormEtAl2010>{{cite journal | last1=Storm | first1=Lance | last2=Tressoldi | first2=Patrizio E. | last3=Di Risio | first3=Lorenzo | title=Meta-analysis of free-response studies, 1992–2008: Assessing the noise reduction model in parapsychology | journal=Psychological Bulletin | volume=136 | issue=4 | year=2010 | doi=10.1037/a0019457 | pages=471–485 | url-status=dead | archive-url=https://web.archive.org/web/20110124055506/http://www.psy.unipd.it/~tressold/cmssimple/uploads/includes/MetaFreeResp010.pdf | archive-date=2011-01-24 | access-date=2010-08-18 | pmid=20565164 | url=http://www.psy.unipd.it/~tressold/cmssimple/uploads/includes/MetaFreeResp010.pdf }}</ref> Hyman (2010) published a rebuttal to Storm ''et al''. concluding that the ganzfeld studies have not been independently replicated and had thus failed to produce evidence for psi.<ref>{{cite journal|author=Hyman R.|author-link=Ray Hyman|year=2010|title=Meta-analysis that conceals more than it reveals: Comment on Storm et al. (2010) |journal=Psychological Bulletin|volume=136|issue=4|pages=486–490|doi=10.1037/a0019676|pmid=20565165 | url = http://drsmorey.org/bibtex/upload/Hyman:2010.pdf | url-status = dead | archive-url = https://web.archive.org/web/20131103081111/http://drsmorey.org/bibtex/upload/Hyman%3A2010.pdf | archive-date = 2013-11-03 }}</ref> According to Hyman, "reliance on meta-analysis as the sole basis for justifying the claim that an anomaly exists and that the evidence for it is consistent and replicable is fallacious. It distorts what scientists mean by confirmatory evidence." Storm ''et al''. published a response to Hyman claiming the ganzfeld experimental design has proved to be consistent and reliable but parapsychology is a struggling discipline that has not received much attention so further research on the subject is necessary.<ref>{{cite journal | last1=Storm | first1=Lance | last2=Tressoldi | first2=Patrizio E. | last3=Risio | first3=Lorenzo Di | title=A meta-analysis with nothing to hide: Reply to Hyman (2010). | journal=Psychological Bulletin | volume=136 | issue=4 | year=2010 | doi=10.1037/a0019840 | pages=491–494 | s2cid=21103309 | pmid=20565166 }}</ref> Rouder ''et al''. in 2013 wrote that critical evaluation of Storm ''et al''.'s meta-analysis reveals no evidence for psi, no plausible mechanism, and omitted replication failures.<ref>{{cite journal | last1=Rouder | first1=Jeffrey N. | last2=Morey | first2=Richard D. | last3=Province | first3=Jordan M. | title=A Bayes factor meta-analysis of recent extrasensory perception experiments: Comment on Storm, Tressoldi, and Di Risio (2010). | journal=Psychological Bulletin | volume=139 | issue=1 | year=2013 | doi=10.1037/a0029008 | pages=241–247 | pmid=23294092 }}</ref>

A 2016 paper examined questionable research practices in the ganzfeld experiments and simulated how such practices could cause erroneous positive results.<ref>{{cite journal|title=Testing for Questionable Research Practices in a Meta-Analysis: An Example from Experimental Parapsychology|last1=Bierman|first1=DJ|last2=Spottiswoode|first2=JP|last3=Bijl|first3=A|year=2016|journal=PLOS ONE|volume=11|issue=5|page=1|doi=10.1371/journal.pone.0153049|quote=We consider [questionable research practices] in the context of a meta-analysis database of Ganzfeld–telepathy experiments from the field of experimental parapsychology. The Ganzfeld database is particularly suitable for this study, because the parapsychological phenomenon it investigates is widely believed to be nonexistent.|pmid=27144889|pmc=4856278|bibcode=2016PLoSO..1153049B|doi-access=free}}</ref>

==Criticism==

[[Image:Richard Wiseman-Emcee-CSICON 2012-Nashville-Opening Remarks-OCT 26 2012.JPG|thumb|200px|right|[[Richard Wiseman]] has suggested various [[sensory leakage]] problems with the autoganzfeld experiments.]]

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.<ref name="Wiseman1996"/>

* ''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.<ref>

{{cite journal

| author = Hyman, Ray

| year = 1994

| month =

| title = Anomaly or Artifact? Comments on Bem and Honorton

| journal = Psychological Bulletin

| volume = 115

| issue = 1

| pages = 19-2419–24

| doi = 10.1037/0033-2909.115.1.19

| author-link = Ray Hyman

| id =

| url =

| format =

| accessdate =

}}</ref>

* ''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 [[fallacy|fallacious]].<ref>{{cite web

''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 [[fallacy|fallacious]]. This does not rule out, however, that it could be telepathy.<ref>

{{cite web

| url = http://skepdic.com/psiassumption.html

| title = The Skeptic's Dictionary: Psi Assumption

| author = Carroll, Robert Todd

| authorlink =

| coauthors =

| date =

| year = 2005

| access-date = 2006-06-23

| month =

| format =

| work =

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| pages =

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| archiveurl =

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| accessdate = 2006-06-23

}}</ref>

Writing in 1985, [[C. E. M. Hansel]] discovered weaknesses in the design and possibilities of sensory leakage in the ganzfeld experiments reported by [[Carl Sargent]] and other parapsychologists. Hansel concluded the ganzfeld studies had not been independently replicated and that "ESP is no nearer to being established than it was a hundred years ago."<ref>{{cite encyclopedia |author-link=C. E. M. Hansel |last=Hansel |first=C. E. M |title=The Search for a Demonstration of ESP |editor-link=Paul Kurtz |editor-last=Kurtz |editor-first=Paul |year=1985 |encyclopedia=A Skeptic's Handbook of Parapsychology |publisher=Prometheus Books |pages=97–127}}</ref>

[[David Marks (psychologist)|David Marks]] in his book ''[[The Psychology of the Psychic]]'' (2000) has noted that during the autoganzfeld experiments the experimenter sat only fourteen feet from the sender's room. Soundproofing tiles were eventually added but they were designed to "absorb sound not to prevent transmission." According to Marks this was inadequate and no different than using any standard internal wall. The door and door frame were also a possible source of sensory leakage and none of these problems were ever eliminated.<ref name="Marks 2000"/>

[[Terence Hines]] wrote in 2003 that the ganzfeld studies could not be said to provide evidence for psi as the alleged evidence disappears as the tightness of [[Scientific control|experimental controls]] is increased. As research progresses [[Variable and attribute (research)|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, there was "no clear way to obtain results showing any psychic phenomenon reliably" and that "the most reasonable conclusion" was that the effect did not exist and had never existed.<ref>{{cite book | last=Hines | first=Terence | title=Pseudoscience and the paranormal | publisher=Prometheus Books | publication-place=Amherst, NY | year=2003 | isbn=978-1573929790 | oclc=50124260 | pages=137–138}}</ref>

In a 2007 review, [[Ray Hyman]] wrote that [[Parapsychology|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. Hyman saw this as a fallacy, as it encouraged parapsychologists to use any peculiarity in the data as a characteristic of psi. Hyman also wrote that 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.<ref name="Hyman2007"/>

{{quote|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<ref name="Hyman2007"/>}}

In their book ''50 Great Myths of Popular Psychology'' (2011), [[Scott O. Lilienfeld]] and colleagues have written that the ganzfeld being a reliable technique is far from being resolved. They concluded that ESP has not been successfully demonstrated in experiments for over 150 years so this is hardly encouraging.<ref>{{cite book | chapter=Myth #3 Extrasensory Perception (ESP) Is a Well Established Scientific Phenomenon | last1=Lilienfeld | first1=Scott |last2=Lynn |first2=Steven Jay |last3=Ruscio |first3=John |last4=Beyerstein |first4=Barry L. | title=50 great myths of popular psychology: shattering widespread misconceptions about human behavior | publisher=Wiley-Blackwell | publication-place=Chichester, West Sussex/Malden, MA | year=2009 | isbn=978-1405131124 | oclc=396172891 | pages=}}</ref>

In a 2013 podcast, [[Brian Dunning (author)|Brian Dunning]] reviewed the flaws of the ganzfeld studies and came to the conclusion the technique had failed as evidence for [[Psi (parapsychology)|psi]] and interest in ganzfeld has declined.<ref name="Dunning2013">{{Skeptoid|id=4348|number=348|title=Ganzfeld Experiments|access-date= November 1, 2013}}</ref>

== Controversy ==

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''.

<blockquote>{{quote|It now appeared that onin one session —&nbsp;– number 9 —&nbsp;– 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.<ref>''{{cite journal |title=A Report of a Visit to Carl Sargent's Laborator''Laboratory |author= Blackmore, Susan |journal=Journal of the Society for Psychical Research, |volume=54 |pages=186–198 |year=1987}}</ref></blockquote>}}

This article, along with further criticisms of Sargent's work from [[Adrian Parker (parapsychologist)|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)<ref>{{cite journal |title=Sceptical fairytales from Bristol |author=Sargent, Carl |journal=Journal of the Society for Psychical Research |volume=54 |pages=208–218 |year=1987}}</ref> in which he did not deny that what Blackmore sawhad occurredobserved, but argued that her conclusions based on those observations were wrong and prejudiced. His Heco-workers also responded, saying that any deviation from protocol was the result of "random errors" rather than any concerted attempt at fraud.<ref>{{cite journal |title=Cheating, psi, and the appliance of science: a reply to Blackmore |author=Harley, Matthews |journal=Journal of the Society for Psychical Research |volume=54 |pages=199–207 |year=1987}}</ref> 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 saidthat organisationorganization was allowed to lapse.<ref>''{{cite book |last=Beloff |first=John |title=Parapsychology: A Concise History'', John Beloff, |publisher=Palgrave MacMillan, |pages=283–284 |year=1997}}</ref>

Writing for ''[[Skeptical Inquirer]]'' in 2018, Blackmore states that Sargent "deliberately violated his own protocols and in one trial had almost certainly cheated." Psychologists reading [[Daryl Bem]]'s review in ''Psychological Bulletin'' would "not have a clue that serious doubt had been cast on more than a quarter of the studies involved". When Blackmore confronted Sargent, he told her "it wouldn't matter if some experiments were unreliable because, after all, we know that psi exists". Blackmore also recounts having a discussion with Bem at a consciousness conference where she challenged him on his support of Sargent and Honorton's research, he replied "it did not matter". Blackmore writes, "But it does matter. ... It matters because Bem's continued claims mislead a willing public into believing that there is reputable scientific evidence for ESP in the Ganzfeld when there is not".<ref name="Blackmore 2018">{{cite journal |last1=Blackmore |first1=Susan |author-link= Susan Blackmore|title=Daryl Bem and Psi in the Ganzfeld |journal=Skeptical Inquirer |date=2018 |volume=42 |issue=3 |pages=44–45 }}</ref>

== See also ==

== See also ==

* [[Parapsychology]]

* [[List of parapsychology topics]]

* [[List of topics characterized as pseudoscience]]

* [[Noumenon]]

* [[Remote viewing]]

* [[Zener cards]]

== References ==

<references/>

== Notes ==

{{notelist}}

*Bem DJ, Honorton C, [http://www.dina.kvl.dk/~abraham/psy1.html "Does Psi Exist? Replicable Evidence for an Anomalous Process of Information Transfer"]. ''Psychological Bulletin'' '''115''' (1), 4-18, 1994.

== References ==

* Bem DJ, Palmer J, Broughton RS, [http://instruct1.cit.cornell.edu/courses/psych113/Bemetal.pdf "Updating the Ganzfeld database: A victim of its own success?"] (PDF). ''Journal of Parapsychology'' '''65''' (3), 207-218, September 2001

{{Reflist|30em}}

==Further reading==

* Goulding A, [http://hdl.handle.net/2077/190 "Mental health aspects of paranormal and psi related experiences, Doctoral Dissertation"]

* [http://www.straightdope.com/mailbag/mganzfeld.html "What's the story on "ganzfeld" experiments?"] {{Webarchive|url=https://web.archive.org/web/20051209012209/http://www.straightdope.com/mailbag/mganzfeld.html |date=2005-12-09 }}. ''The Straight Dope'', December 14, 2000.

* Andrew Colman. (1995). ''Controversies in Psychology''. Longman Pub Group. {{ISBN|978-0582278035}}

* [[C. E. M. Hansel]]. (1989). ''The Search for Psychic Power: ESP and Parapsychology Revisited''. [[Prometheus Books]]. {{ISBN|978-0879755331}}

* {{cite journal | url=http://www.mceagle.com/remote-viewing/refs/science/air/hyman.html | journal=The Journal of Parapsychology | date=1995 | title=Evaluation of Program on Anomalous Mental Phenomena | author=Ray Hyman | author-link=Ray Hyman | access-date=2007-01-10 | archive-date=2017-06-16 | archive-url=https://web.archive.org/web/20170616174455/http://mceagle.com/remote-viewing/refs/science/air/hyman.html | url-status=dead }}

* {{cite journal | url=http://www.csicop.org/si/show/new_analyses_raise_doubts_about_replicability_of_esp_findings/| title=New Analyses Raise Doubts About Replicability of ESP Findings | author=Scott O. Lilienfeld | journal=Skeptical Inquirer |date=November–December 1999 | author-link=Scott O. Lilienfeld }}

* {{cite book | last=Neher | first=A. | title=Paranormal and Transcendental Experience: A Psychological Examination | publisher=Dover Publications | year=2011 | isbn=978-0486144863 | url=https://books.google.com/books?id=LkPSTzhYNTkC }}

* {{cite book | title=The Conscious Universe: The Scientific Truth of Psychic Phenomena | author=Dean Radin | publisher= HarperOne | isbn=978-0062515025 | ref=ConsciousUniverse | year=1997| author-link=Dean Radin }}

* [[Gordon Stein]]. (1996). ''The Encyclopedia of the Paranormal''. Prometheus Books. {{ISBN|978-1573920216}}

* [[Victor J. Stenger|Victor Stenger]]. (1990). ''Physics and Psychics: The Search for a World Beyond the Senses''. Prometheus Books. {{ISBN|978-0879755751}}

* Leonard Zusne and Warren Jones. (1989). ''Anomalistic Psychology: A Study of Magical Thinking''. Psychology Press. {{ISBN|978-0805805086}}

==External links==

*[http://www.straightdope.com/mailbag/mganzfeld.html ''What's the story on "ganzfeld" experiments?''], The Straight Dope, December 14, 2000.

* [http://www.koestler-parapsychology.psy.ed.ac.uk/Psi.html Koestler Parapsychology Unit: Testing Psi]

* [http://www.skepdic.com/ganzfeld.html ''The Skeptic's Dictionary'': "Ganzfeld"]

{{Parapsychology}}

*[http://www.csicop.org/si/9911/lilienfeld.html ''New Analyses Raise Doubts About Replicability of ESP Findings''], Scott O. Lilienfeld, ''Skeptical Inquirer'', November/December 1999

{{DEFAULTSORT:Ganzfeld Experiment}}

*[http://skepdic.com/ganzfeld.html ''The Skeptic's Dictionary'': "ganzfeld"]

[[Category:Parapsychology]]

[[Category:Pseudoscience]]

*[http://www.skepticreport.com/psychicpowers/ganzfeld.htm Skeptic Report, ''A History of Psi in the Ganzfeld'', Andrew Endersby]

*''[http://anson.ucdavis.edu/~utts/91a-menu.html Replication and meta-analysis in parapsychology]'', Jessica Utts, published in "Statistical Science," 1991, Vol. 6., No. 4, 363-403

[[Category:Psychology experiments]]

[[Category:Parapsychology]]

[[Category:Telepathy]]

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