Ganzfeld Experiments

The true history of the experiment that is said to present the strongest evidence yet for telepathic abilities.

by Brian Dunning

Filed under Paranormal

Skeptoid #348
February 5, 2013
Podcast transcript | Listen | Subscribe
Also available in Russian

Today we're going to enter a quiet, darkened room, sit comfortably, and prepare to receive psychic imagery, in what's often claimed to be the most convincing evidence for the reality of psi — psychic abilities. The idea of being able to transmit thoughts from one person to another is so compelling that there's never been a shortage of researchers hoping to find a way to develop it. We all wish we could have such a superpower, so we all want this to be true. Today's subject is ganzfeld experiments. Ganzfeld is German for "whole field", referring to its method of replacing the whole of your field of perception. Let's take a close look and see what it is, how it works, and — most importantly — whether it does indeed promise to be proof of psi.

A ganzfeld state is a bit different from sensory deprivation, as made famous in the movie Altered States. In sensory deprivation, the idea is to remove all stimuli, audio, visual, thermal, and tactile. Ideally the subject is placed in an isolation tank, a coffin-like device in which you float in a dense saline solution, the temperature is a constant, comfortable ambient temperature, and it's completely dark and quiet. You see, hear, and feel nothing. Sensory deprivation has often been used recreationally, both with and without hallucinogenic drugs, for its ability to make the imagination seem surprisingly real, given the lack of competing stimuli.

However, in ganzfeld, the idea is to instead provide homogenous stimuli. The subject, called the "receiver", sits comfortably in a recliner, wearing headphones playing gentle white noise. The room is bathed in red light and the receiver wears translucent cups over the eyes, so all they see is a uniform, featureless red. They are relaxed and cozy. That's the physical setting of the experiment. Two other people are involved: an experimenter and a "sender". The sender, in an isolated room where they cannot be seen or heard by the receiver, concentrates for 30 minutes on a "target", which is some object or video clip or something. Throughout the 30 minutes, the receiver is supposed to verbally recite what they see or imagine. The experimenter, who is also supposed to be isolated from both the sender and the receiver, records what the receiver says, and usually keeps notes about what they describe.

At the end of the 30 minutes, the receiver is shown the actual target upon which the sender was focusing, presented alongside with three other control objects. The receiver guesses which of the four most closely resembles their impressions during the ganzfeld session. Pure chance predicts a 25% hit rate. But ganzfeld experiments became famous within the parapsychology community because experimenters consistently found a significantly higher hit rate; closer to 35%.

The history of ganzfeld experimentation is essentially the history of a particular battle between skeptics and believers; a cordial battle, but a battle nevertheless. Beginning in the 1970s, the leading proponent was American parapsychologist Charles Honorton, a staunch believer in psychic abilities, who was dedicated to finding a reliable scientific method of establishing the reality of psi. Honorton's idea was that whatever psi abilities many people may have is lost in the sea of constant stimuli that we're all receiving all day long. We see, we hear, we touch, we think, to such a degree that if we did receive a psychic impression we'd never recognize it as such. So by placing subjects into a ganzfeld state, it's thought that the signal-to-noise ratio would be increased, by shutting off all that noise, and subjects might be more likely to recognize a psychic transmission.

Across the line of battle was Ray Hyman, at the time a professor of psychology at Harvard. In the 1980s he came across Honorton's body of work, said to be the best evidence yet for psi. Hyman studied it carefully, and came away unconvinced. In his assessment, the positive results so flaunted by the parapsychologists was due to methodological error. In 1985, Hyman published an article in the Journal of Parapsychology called "The Ganzfeld Psi Experiment: A Critical Appraisal".

Unimpressed right back, Honorton published — in that very same issue of the journal — "Meta-Analysis of Psi Ganzfeld Research: A Response to Hyman". Clearly, there was a difference of opinion.

Before we look at what happened next, let's hear out both Honorton and Hyman to see exactly what was right or wrong with the research. Most of this involved what are called meta analyses, which is when you combine the results of multiple studies with the goal of getting a better idea of what the whole body of research in a field has concluded. Meta analyses are tricky animals, because studies can be conducted in so many different ways, and are often of greatly varying quality. All sorts of statistical methods can be employed (rightly or wrongly) to try and account for and control these differences. It's not surprising — in fact it's to be expected — that researchers can come up with greatly differing findings doing meta analyses on the same set of studies.

Hyman brought a considerable amount of skepticism to the table, so I was expecting his article to find all sorts of problems with Honorton's work, which covered 42 studies in which 55% showed positive evidence of psi. Hyman did report problems, however his own corrected analysis found not the random chance result of 25%, but a still-significant 30%, which, in itself, appears to still represent pretty amazing evidence that Honorton's receiving subjects were in fact receiving some kind of impressions from the senders. However, not so fast. The criticisms that Hyman found were inadequate randomization; sensory leakage (meaning that in some cases, the receivers could actually hear what was going on in the sender's room next door; in others, it was possible for things like the sender's fingerprints to be visible on the target object for the receiver to see); and inappropriate statistical analysis.

Mainly, Hyman felt that Honorton's work suffered from a type of statistical complication called multiple testing. In a nutshell, multiple testing is when you take more and more variables into account between two groups; sooner or later you're going to find more and more differences between them. These variables included the different ways that researchers had categorized the senders and receivers, cross referencing them to the results. They found that subjects were more likely to have positive results if they had been educated in a creative field; if they already had a strong belief in psychic powers; if they were extroverted; and if the experiment was conducted in a warm and welcoming atmosphere. Hyman believed that the positive results reported by Honorton were due, at least in part, to multiple testing effects that inappropriately considered these types of variables. Hyman also found that the "file drawer effect" came into play, which is when studies are abandoned when they end up not showing any interesting results. Thus, the body of published work was inappropriately skewed to include those results which showed a positive result, which is going to happen sometimes simply due to random variances. Hyman figured that, working backwards and accounting for the degrees to which various weaknesses were present in each of the studies, the actual size of the effect was zero. His closing line was:

It is concluded that this data base is too weak to support any assertions about the existence of psi.

Honorton's reply in the journal was in kind. He acknowledged all of these potential weaknesses, but explained how he had accounted for them, and still insisted that the results supported the existence of psi. This whole discussion got about as deep into statistics as anyone might reasonably (or unreasonably) want to go; but the net result is that the men had a disagreement on the analysis of the existing body of work. So now let's look at what happened next.

It was quite refreshing, and something that I wish I've seen more often. Honorton and Hyman got together and collaborated on a new article, hoping to find an analysis they could agree on. It was published in the same journal in 1986, entitled "A Joint Communique: The Psi Ganzfeld Controversy". Essentially, Honorton and Hyman agreed on the methodological weaknesses and on ways to fix them, but were not able to come to a consensus on the proper analysis of the existing studies. They concluded:

We continue to differ over the degree to which the effect constitutes evidence for psi, but we agree that the final verdict awaits the outcome of future experiments conducted by a broader range of investigators and according to more stringent standards.

The result of this collaboration was a process called the autoganzfeld study. This was a computer controlled version of the ganzfeld experiment, where randomization and the other methodological weaknesses identified by Hyman and others were eliminated. In expressing his satisfaction with the potential of the autoganzfeld process, Hyman wrote:

Honorton's experiments have produced intriguing results. [If] independent laboratories can produce similar results with the same relationships and with the same attention to rigorous methodology, then parapsychology may indeed have finally captured its elusive quarry.

So with replication as the goal, many researchers at many locations took up the torch and began performing autoganzfeld tests. Publications continued to be produced, many of them continuing to find positive — if small — results. It was this decade and a half of replication efforts that led to the next major publication on ganzfeld experiments. Honorton and his collaborator, Daryl Bem, published this time in a more mainstream journal, Psychological Bulletin, in 1994 (after Honorton's death). Their conclusion was optimistic, but measured:

The autoganzfeld studies by themselves cannot satisfy the requirement that replications be conducted by a "broader range of investigators." Accordingly, we hope that the findings reported here will be sufficiently provocative to prompt others to try replicating the psi ganzfeld effect.

Tip Skeptoid $2/mo $5/mo $10/mo One time

Their article failed to convince. In 1999 the Bulletin published a thorough critique of Honorton and Bem's paper. Its authors were experimental psychologists Richard Wiseman and Julie Milton, and it focused on the failure of the popularly reported positive results to be replicated by independent researchers. After a deep discussion of all the problems found with Honorton's body of work, Wiseman and Milton concluded:

The new ganzfeld studies show a near-zero effect size and a statistically nonsignificant overall cumulation... The autoganzfeld results have not been replicated by a "broader range of researchers." The ganzfeld paradigm cannot at present be seen as constituting strong evidence for psychic functioning.

With the death of Charles Honorton in 1992, interest in ganzfeld has declined somewhat, though psi researchers such as Dean Radin have continued to support it. The best lesson to be learned from ganzfeld experimentation is not so much that the technique has failed as evidence for psi, but rather that it is indeed possible for skeptics and believers to work together in a productive, positive, and collaborative way to find the truth. Hyman and Honorton showed us that the mainstream and the fringe need not always be squared off with an us-vs.-them mentality, and reminded us that the best researchers, whether they're right or wrong, embrace their critics and work with them to improve the state of our knowledge.

Brian Dunning

© 2013 Skeptoid Media Copyright information

References & Further Reading

Bem, D. Encyclopedia of the Paranormal. Buffalo: Prometheus Books, 1996. 291-296.

Frazier, K. "Improving Human Performance: What about Parapsychology?" Skeptical Inquirer. 1 Jul. 1988, Volume 13, Number 1: 34-45.

Honorton, C. "Meta-Analysis of Psi Ganzfeld Research: A Response to Hyman." Journal of Parapsychology. 1 Sep. 1985, Volume 49: 51-91.

Hyman, R. "The Ganzfeld Psi Experiment: A Critical Appraisal." Journal of Parapsychology. 1 Sep. 1985, Volume 49: 3-49.

Hyman, R., Honorton, C. "A Joint Communique: The Psi Ganzfeld Controversy." Journal of Parapsychology. 1 Jan. 1986, Volume 50: 351-364.

Lilienfeld, S. "New Analyses Raise Doubts about Replicability of ESP Findings." Skeptical Inquirer. 1 Nov. 1999, Volume 23, Number 6: 9, 12.

Milton, J., Wiseman, R. "Does Psi Exist? Lack of Replication of an Anomalous Process at Information Transfer." Psychological Bulletin. 1 Jan. 1999, Volume 125, Number 4: 387-391.

Reference this article:
Dunning, B. "Ganzfeld Experiments." Skeptoid Podcast. Skeptoid Media, 5 Feb 2013. Web. 8 Oct 2015. <>


10 most recent comments | Show all 78 comments

Tom: Yes, the possibility of fraud can never be totally eliminated from an experiment. Why? Because no experiment is EVER perfect or ABSOLUTELY free from human error. Even Susan Blackmore acknowledges this. The odds of his looking through a trapdoor or some other convoluted method is just ridiculous and highly improbable. Prescott, BTW, agrees with me.

Lukas: "Nicolas claims he has no bias and dogma? So why he is writing this?"

Because I think you're incorrect, and I'm very annoyed with being talked down to. I don't WANT to be this much of a jerk.

"There is no evidence."

OK. Statistically significant findings apparently don't count as evidence. Fine.

"All you have are meta-studies of studies and some weak statistics which can be made even Steven Novella pointed that out and that in Neuroscience and other sciences:"

They're not weak. They're strong. Novella, again, belongs to the James Randi vein, and he doesn't understand how statistics work.

"Second his attacks on skeptics show his hatred and bias:"

I don't "have hatred". I'm just annoyed. Carroll doesn't understand how stats or investigation work, and I explained why.

"Second these people knew each other for two years. I read it pathetic. This is not science this is confirming believes and with a pathetic study to milk money."

Er... no. This is a science, not a will to believe. I'm sorry if the effects aren't strong enough "for you", but they're still scientifically and clinically strong.

That's it. I'm done.

Nicolas, Plymouth, MI
March 7, 2014 4:44am

"Because I think you're incorrect, and I'm very annoyed with being talked down to. I don't WANT to be this much of a jerk."

So why did you wrote that? Why do you attack people? Have you some anger issues or what??

"OK. Statistically significant findings apparently don't count as evidence. Fine."

Yeah from pathetic and weak studies like that? Sure if that is evidence for ya then believe.

"They're not weak. They're strong. Novella, again, belongs to the James Randi vein, and he doesn't understand how statistics work."

LOL!! Sorry this made me laugh. Steven Novella who has a Dr. degree and is a known neurosientists does not know how statistics work?? LOL again. Yeah I know he is with Randi and?

Sure Nicolas you know how the whole world works and everyone who does not agrees with you knows nothing.. Please stop embarrassing yourself. You again show your big hatred for skeptics and your hard beliefs..

"I don't "have hatred". I'm just annoyed. Carroll doesn't understand how stats or investigation work, and I explained why."

I think Carroll understands more then you do.

"Er... no. This is a science, not a will to believe. I'm sorry if the effects aren't strong enough "for you", but they're still scientifically and clinically strong."

Yeah if you like cheap studies made by believers with cheap tricks. Then you can rest. For you is PSI proven beyond any doubt.

Okay I am done. I had to reply because this was the kicker..It made my day thanks.

Lukas, Prague
March 7, 2014 5:33am

Nicolas you have contradicted yourself:

"the possibility of fraud can never be totally eliminated from an experiment. Why? Because no experiment is EVER perfect or ABSOLUTELY free from human error."

Firstly this opinion is not shared by all parapsychologists. Dean Radin or Charles Tart wouldn't agree for example. Secondly what you said there contradicts your comments on the Ganzfeld. You wrote:

"They're DESIGNED so that other things are ruled out, including sensory leakage."

But now you admit the possibility of fraud in the ganzfeld cannot be ruled out! Therefore you have contradicted yourself and your argument breaks down.

If you are accepting the possibility of fraud in psi experiments then those experiments can not be said to be evidence for psi it's that simple any scientist would tell you this (See Hansel's book). Psi can only be said to be demonstrated when the possibility of sensory leakage or tricks are ruled out but after 130 years no experiment has shown this. Nicolas I suggest you do some research into scientific controls and some reading up on Occam's razor which has been very useful in science. Regards.

Tom, UK
March 7, 2014 11:22am

Parapsychology is with us 130 or even more and so far has produced nothing of interest besides bad studies and wishful thinking. Other science disciplines produce new and major stuff every day. So I think there must be somewhere a error because if parapsychology would be of use we would already have something.

Also wanted to add that Dr. Steven Novella teaches at Yale:

So I think he knows science and also statistics.

Another problem is that a lot of psychics are frauds and were caught and are even facing jail:

This is just the top of the iceberg. Also last thing I wanted to add. I will not be replying here for the weekend. I need a pause from all this nonsense and I have a normal life to live also not just looking into some fantasies all the time. Have a nice weekend..

Lukas, Prague
March 7, 2014 11:35am

Oh, for God's sake. Do I really have to spell this out for you?

"But now you admit the possibility of fraud in the ganzfeld cannot be ruled out! Therefore you have contradicted yourself and your argument breaks down."

***Sigh*** NO! The entire point is that, once you rule out sensory leakage by soundproof rooms, any other idea of sensory leakage becomes ad-hoc and highly, highly improbable. And yes, both Hyman and Radin believe this, and Radin quotes this from Hyman in THE CONSCIOUS UNIVERSE (pg. 248). As Ray Hyman said in a 1984 Nova interview, "You cannot make a perfectly 100 percent fraud-proof experiment. This would apply to all science."

That's it. I'm done talking with you two. You persist in your beliefs, your materialistic dogma, and your complete ignorance, with the vague disguise of being "scientific" (despite the fact that you wouldn't know a valid clinical/psychological experiment if it dropped out of the sky). Tom, stop this "regards" crap. I don't need your arrogance, and I don't need to deal with your stupidity. Leave me alone.

Nicolas, Plymouth, MI
March 7, 2014 12:22pm

"NO! The entire point is that, once you rule out sensory leakage by soundproof rooms, any other idea of sensory leakage becomes ad-hoc and highly, highly improbable."

You misunderstand the scientific method. Hansel has it correct. It doesn't matter if you consider a naturalistic explanation "improbable", if the possibility of fraud or sensory leakage are possible in an experiment and not ruled out then any "paranormal" or magical explanation like "psi" by default are automatically disregarded for the naturalistic explanation. This is Occam's razor something you have ignored in all of your posts. Extraordinary claims require extraordinary evidence. Science does not discard a possible natural explanation for a "paranormal" one. Never ever. Only parapsychologists do this because they practice pseudoscience and are anti-scientific. Parapsychology does not make testable predictions and all it's proponents do these days is hide behind statistics because they can't show any alleged "psi" phenomena scientifically.

"You persist in your beliefs, your materialistic dogma"

Science is material, belief doesn't come into it.

Tom, UK
March 7, 2014 2:45pm

The whole problem of this discussion is that you want to believe Nicolas. Also wanted to add that Dr. Steven Novella teaches on Yale so I think he knows a lot about statistics.

Another problem is that a lot of psychics were accused of fraud and some of them are even in jail. Just google Psychic jailed in doubtful news. (I posted a longer commentary but it did not show up here because there were many links in it.)

Also this is my last post for the weekend. I want to have break of this whole "pseudo" business for the weekend. I wish you all here a nice weekend.

Lukas, Prague
March 7, 2014 10:34pm

What Dunning has said is important:

"The best lesson to be learned from ganzfeld experimentation is not so much that the technique has failed as evidence for psi, but rather that it is indeed possible for skeptics and believers to work together in a productive, positive, and collaborative way to find the truth."

If it wasn't for Ray Hyman none of those original flaws in the ganzfeld would have been found. Hyman was a scientist who went away from his career to spend a large amount of time look at the ganzfeld. Parapsychologists should respect this. Instead of psi-believers always accusing scientists of being "materialists" or "pseudoskeptics" they should acknowledge that scientists have helped parapsychology eliminate errors in their experiments. The parapsychologists rarely find the errors or sensory leakage themselves. Take for example Rhine's errors with his experiments most of them were pointed out by critics of parapsychology which he later acknowledged.

Tom, UK
March 8, 2014 12:23pm

The really big thing regarding Ganzfeld is the ability to reach the theta brain state quickly and easily. And the benefits of the theta state are numerous: deep relaxation or meditation, better intuition, quicker learning, possibility for reprogramming your subconscious mind, etc. Now you can try it with this Ganzfeld Light Mask: or
The whole Psi "haunting" is really ridiculous, isn't it?

Paul, UK
May 26, 2014 3:31pm

Time seems to have stopped in 1999 according to this podcast. Actually, several additional meta-analyses of ganzfeld studies were published after 1999, all of them showing a highly significant effect. The latest being Storm et al.'s 2010 meta-analysis. In addition, Milton and Wiseman's 1999 meta-analysis was flawed as the statistical calculations were done incorrectly. A re-analysis by Jessica Utts demonstrated that in fact Milton and Wiseman's study also shows a significant effect, and this was admitted by Wiseman. Therefore the ganzfeld has not at all been abandoned as this podcast suggests.

Andras, Hungary
September 1, 2014 4:19pm

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