甘兹菲尔德实验

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 hallucinations. 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 dreams 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" (a catch-all term used in parapsychology to denote anomalous psychic abilities) might work. Honorton believed that by reducing the ordinary sensory input, "psi-conductive states" would be enhanced and "psi-mediated information" could be more effectively transmitted.

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 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.

Analysis of results

Early experiments

Between 1974 and 1982, 42 ganzfeld experiments were performed by parapsychologists. 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.

Hyman discovered flaws in all of the 42 ganzfeld experiments, and, to assess each experiment, he devised a set of 12 categories of flaws.

Criticism

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 receivers themselves could hear the video.

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.

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.

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.