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PSI PHENOMENA
Daryl J. Bern
Cornell University
Experimental Evidence
Debate over the Evidence
Replication Problem
Inadequate Controls
File-Drawer Problem
Anecdotal Evidence
Skepticism about
Psi
Extraordinary Claims
Skepticism of Psychologists
References
Prepared for inclusion in Atkinson, R, L, Atkinson, R. C., Smith, E. E., & Bern, D. J.
(1990). Introduction to Psychology
(10th Ed). San Diego: Harcourt Brace Jovanovich.
I am grateful to Charles Honorton, Robert Rosenthal, and Marcello Truzzi for comments
on earlier drafts.
Still subject to editing. Please do not quote without permission.
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Psi Phenomena
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PSI PHENOMENA
Is it possible for us to acquire information about the world in ways that do not involve
stimulation of the known sense organs or to influence physical events by purely mental means?
These questions are the source of controversy over the existence ofpsi, processes of
information and/or energy exchange not currently explicable in terms of known science. The
phenomena of psi are the subject matter of parapsychology (“beside psychology”) and include
the following:
1. Extrasensory Perception (ESP). Response to external stimuli without
sensory contact.
a. Telepathy. Response to the mental state of another person without the
mediation of any known channel of sensory communication (for example,
identifying a playing card merely being thought of by another person)
b. Clairvoyance. Response to objects or events that do not provide a stimulus
to any known sense (for example, identifying a concealed playing card
whose identity is unknown to anyone)
c. Precognition. Response to a future event that could not be anticipated
through any known inferential process (for example, predicting which digit a
random number generator will generate on the next trial)
2. Psychokinesis (PK). Mental influence over physical events without the
mediation of any known physical force (for example, influencing which digit a
random number generator will generate on the next trial)
Experimental
Evidence
Most parapsychologists consider themselves to be scientists applying the usual rules of
scientific inquiry to admittedly unusual phenomena. Yet the phenomena of psi are so
extraordinary and so similar to what are widely regarded as superstitions that some scientists
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Psi Phenomena
declare psi to be an impossibility and reject the legitimacy of parapsychological inquiry. Such
a priori judgments are out of place in science; the real question is whether the empirical
evidence is acceptable by scientific standards. Many psychologists who are not yet convinced
that psi has been demonstrated are nevertheless open to the possibility that new evidence might
emerge that would be more compelling. For their part, many parapsychologists believe that
several recent experimental procedures either provide that evidence already or hold the potential
for doing so. We shall examine one of the most promising of these, the ganzfeld procedure.
The ganzfeld procedure tests for telepathic communication between a subject acting as
the “receiver” and another person who serves as the “sender.” The subject is sequestered in an
acoustically-isolated room and placed into a mild form of perceptual isolation: translucent
ping- pong ball halves are taped over the eyes and headphones are placed over the ears; diffuse
red light illuminates the room, and white noise is played through the headphones. (White noise
is a random mixture of sound frequencies similar to the hiss made by a radio tuned between
stations.) This homogeneous visual and auditory environment is called the Ganzfeld, a German
word meaning “total field.”
The sender is sequestered in a separate acoustically-isolated room, and a visual stimulus
(picture, slide, or brief videotaped sequence) is randomly selected from a large pool of similar
stimuli to serve as the “target” for the session. While the sender concentrates on the target, the
subject attempts to describe it by providing a continuous verbal report of his or her ongoing
imagery and free associations. Upon completion of the session, the subject is presented with
four stimuli—one of which is the target—and asked to rate the degree to which each matches
the imagery and associations experienced during the ganzfeld period. A “direct hit” is scored if
he or she assigns the highest rating to the target. (In some studies, individuals unconnected
with the experiment also attempt to match a transcript of the subject’s verbal report to the
target.)
More than 50 ganzfeld experiments have been conducted since the procedure was first
introduced in 1974. An overall analysis of 28 studies reported through 1981—comprising 835
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ganzfeld sessions conducted in 10 different laboratories—reveals that subjects selected the
target 38% of the time on the average. (Because there are 4 alternatives, we would expect a
success rate of 25% if only chance were operating.) Statistically this result is highly significant:
the probability that it could have arisen by chance is less than one in a billion (Honorton,
1985).
Debate over the Evidence
In 1985 and 1986, the Journal ofParapsychology published an extended examination
of the ganzfeld studies, focusing on a debate between Ray Hyman, a cognitive psychologist
and critic of parapsychology, and Charles Honorton, a parapsychologist and major contributor
to the ganzfeld database. They agree on the basic quantitative results but disagree on points of
interpretation (Hyman, 1985; Hyman & Honorton, 1986; Honorton, 1985). We shall use their
debate as a vehicle for examining the major issues involved in evaluating all claims of psi.
Replication Problem
In science generally, a phenomenon is not considered
established until it has been observed repeatedly by several researchers. Accordingly, the most
serious criticism of parapsychology is that it has failed to produce a single demonstration of psi
that can be reliably replicated (successfully reproduced) by other investigators. Even the same
investigator testing the same individuals over time may obtain significant results on one
occasion but not on another. The ganzfeld procedure is no exception; fewer than half (43%) of
the 28 studies analyzed in the debate yielded statistically significant results.
The parapsychologists’ most effective response to this criticism actually comes from
within psychology itself. Many statisticians and psychologists are dissatisfied with
psychology’s focus on the significance level as the sole measure of a study’s success. As an
alternative, they are increasingly adopting the technique of meta-analysis, a technique that treats
the accumulated studies of a particular phenomenon as a single grand experiment and each
study as a single observation. Thus any study that obtains results in the positive direction
even though it may not be statistically significant itself—contributes to the overall strength and
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