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Does Psi Exist?
Replicable Evidence for an
Anomalous Process of Information Transfer
Daryl J. Bern
Charles Honorton
Cornell University
University of Edinburgh
Most academic psychologists do not yet accept the existence.of psi, anomalous Pr^
e8^
of in
formation or energy transfer (like telepathy or other forms of extrasensory perception
that are
currently unexplained in terms of known physical or biological mechanisms. We bel eye that
the replication rates and
effect sizes achieved by one particular experimental method, the
ganzfeld procedure, are now sufficient to warrant bringing this body of data to the attenhon ot
the
wider
psychological community. We review competing meta-analyses
of the
ganzfeld
database, one by Hyman (1985), a skeptical cntic of psi research, the other by Honorton (1985),
a parapsychologist and major contributor to the ganzfeld database Next we s^m^ the re-
sults of 11 new ganzfeld studies that comply with guidelines jointly authored by Hyman and
Honorton (1986)
Finally, we discuss issues of replication and theoretical explanation.
The term psi denotes anomalous processes of informa-
tion or energy transfer, processes like telepathy or other
forms of extrasensory perception that are currently unex-
plained in terms of known physical or biological mecha-
nisms. The term is purely descriptive:
It neither implies
that such anomalous phenomena are paranormal nor con-
notes anything about their underlying mechanisms.
Does psi exist? Most academic psychologists don t think
so A survey of over 1,100 college professors in the United
States found that 55% of natural scientists, 66% of social
scientists (excluding psychologists), and 77% of academics
in the arts, humanities, and education believed that ex-
trasensory perception
is either an established fact or a
likely possibility. The comparable figure for psychologists
was only 34%. Moreover, an equal number of psycholo-
gists declared extrasensory perception to be an impossibil-
ity, a view expressed by only 2% of all other respondents
(Wagner & Monnet, 1979).
.
.
-
Psychologists are probably more skeptical about psi tor
several
reasons.
First,
we
believe
that
extraordinary
claims require extraordinary proof. And although our col-
leagues from other disciplines would probably agree with
Sadly, Charles Honorton died of a heart attack on November
4, 1992, nine days before this article was accepted for publication.
He was 46. Parapsychology has lost one of its most valued con-
tributors. I have lost a valued friend.
This collaboration had its origins in a 1983 visit I mde to
Honorton’s
Psychophysical
Research
Laboratories
(PKL)
in
Princeton, New Jersey,
as one of several outside consultants
brought in lo examine the design and implementation of the ex-
perimental protocols.
Preparation of this article was supported, m part, by grants to
Charles Honorton from the American Society for Psychical Re-
search and the Parapsychology Foundation, both of New York
City. The work at PRL summarized in the second half of this ar-
ticle was supported by the James S. McDonnell Foundation of bt.
Louis, Missouri, and by the John E. Fetzer Foundation of Kala-
mazoo, Micliigan.
.
,
_
_
,
Helpful comments on earlier drafts were received from ilebo-
rah Delanoy, Edwin May, Donald McCarthy, Robert Morris, John
Palmer, Robert Rosenthal, Lee Ross, Jessica Utts, Philip 4im-
bardo, and two anonymous reviewers.
Correspondence should be addressed to Daryl J. Bern, Depart-
ment of Psychology, Uris Hall, Cornell University,
Ithaca, NY
14853.
this dictum, we are more likely to be familiar with the
methodological and statistical requirements for sustaining
such claims—as well as with previous claims that failed
either to meet those requirements or to survive the test of
successful replication. Even for ordinary claims, our con-
ventional statistical criteria are conservative. The sacred
p = .05 threshold is a constant reminder that it is far more
sinful to assert that an effect exists when it does not (the
Type I error) than to assert that an effect does not exist
when it does (the Type II error).
Second, most of us distinguish sharply between phe-
nomena whose explanations are merely obscure or contro-
versial
(e.g., hypnosis) and phenomena
like
psi, which
would appear
to
fall
outside
our
current explanatory
framework altogether. (Some would characterize this as
the difference between the unexplained and the inexplica-
ble.) In contrast, many laypersons treat all exotic psycho-
logical phenomena as epistemologically equivalent—many
even consider d6jh vu to be a psychic phenomenon. The
blurring of this critical distinction is aided and abetted by
the mass media, “new age” books and mind-power courses,
and by “psychic” entertainers who present both genuine
hypnosis and fake “mindreading” in the course of a single
performance.
Accordingly,
most
laypersons
would
not
have to revise their conceptual model of reality as radi-
cally as we would in order to assimilate the existence of
psi. For us, psi is simply more extraordinary.
And finally, research in cognitive and social psychology
has sensitized us to the errors and biases that plague in-
tuitive attempts to draw valid inferences from the data of
everyday
experience
(Gilovich,
1991;
Nisbett &
Ross,
1980; Tversky & Kahneman, 1971). This leads us to give
virtually no probative weight to anecdotal or journalistic
reports of psi—the main source cited by our academic col-
leagues as evidence for their beliefs about psi (Wagner &
Monnet, 1979).
Ironically, however, psychologists are probably not more
familiar than others with recent experimental research on
psi. Like most psychological research, parapsycho ogical
research is reported primarily in specialized journals; un-
like most psychological research, however, contemporary
parapsychological
research
is
not
usually
summarized
in
psychology's
textbooks
mainstream journals. For example* only
o
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tory psychology textbooks recently surveyed even men-
tions the experimental procedure reviewed in this article,
a procedure that has been in widespread use since the
early 1970s (Roig, Icochea, & Cuzzucoli, 1991). Other sec-
ondary sources
for nonspecialists are frequently inaccu-
rate in
their descriptions of parapsychological research
(Child, 1985; Palmer, Honorton, & Utts, 1989).
ThiB situation may be changing. Discussions of modem
psi research have recently appeared in a widely-used in-
troductory textbook (Atkinson, Atkinson, Smith, & Bern,
1990, 1993), two mainstream psychology journals (Child,
1985; Rao & Palmer, 1987), and a scholarly but accessible
book for nonspecialists (Broughton, 1991). The purpose of
the present article is to supplement these broader treat-
ments with a more detailed, meta-analytic presentation of
evidence issuing from a single experimental method: the
ganzfeld procedure. We believe that the replication rates
and effect sizes achieved with this procedure are now suf-
ficient to warrant bringing this body of data to the atten-
tion of the wider psychological community.
The Ganzfeld Procedure
By the 1960s, a number of parapsychologists had be-
come dissatisfied with the familiar ESP testing methods
pioneered by J. B. Rhine at Duke University in the 1930s.
In
particular, they
felt that the repetitive forced-choice
procedure in which a subject repeatedly attempts to select
the correct “target” symbol from a set of fixed-alternatives
failed to capture the circumstances that characterize re-
ported instances of psi in everyday life.
Historically, psi has often been associated with medita-
tion, hypnosis, dreaming, and other naturally occurring or
deliberately induced altered states of consciousness. For
example, the view that psi phenomena can occur during
meditation is expressed in most classical texts on medita-
tive techniques; the belief that hypnosis is a psi-conducive
state dates
all the way back to the days of early mes-
merism (Dingwall, 1968); and cross-cultural surveys indi-
cate that most reported “real-life” psi experiences are me-
diated through dreams (Green, 1960; Prasad & Stevenson,
1968; Rhine, 1962; Sannwald, 1959).
There are now reports of experimental evidence consis-
tent with these anecdotal observations. For example, sev-
eral laboratory investigators report that meditation facili-
tates psi performance (Honorton, 1977). A meta-analysis
of 25 experiments on hypnosis and psi conducted between
1945-1981 in 10 different laboratories suggests that hyp-
notic induction also facilitates psi performance (Schechter,
1984). And dream-mediated psi was reported in a series of
experiments conducted at Maimonides Medical Center in
New York, and published between 1966 and 1972 (Child,
1985; Ullman, Krippner, & Vaughan, 1973).
In
the Maimonides
dream
studies,
two
subjects—
a
“receiver” and a “sender”—spent the night in a sleep labo-
ratory. The
receiver’s brainwaves and
eye movements
were monitored as he or she slept in an isolated room.
When the receiver entered a period of REM sleep, the ex-
perimenter pressed a buzzer that signaled the sender-
under the supervision of a second experimenter—to begin
a sending period. The sender would then concentrate on a
randomly chosen picture (the “target”) with the goal of in-
fluencing the content of the receiver’s dream.
Toward the end of the REM period, the receiver was
awakened and asked to describe any dream just experi-
enced. This procedure was repeated throughout the night
with the same
target. A transcription of the
receiver’s
dream reports was given
to outside judges who blindly
rated the similarity of the night’s dreams to several pic-
tures, including the target. In some studies similarity rat-
ings were also obtained from the receivers themselves.
Across several variations of the procedure, dreams were
judged to be significantly more similar to the target pic-
tures than to the control
pictures in the judging
sets.
(Failures to replicate the Maimonides
results are also re-
viewed by Child (1985).)
These
several
lines of evidence suggested a working
model of pBi in which psi-mediated information is concep-
tualized as a weak signal that is normally masked by in-
ternal somatic and external sensory “noise." By reducing
ordinary sensory input, these diverse psi-conducive states
are presumed to raise the signal-to-noise
ratio, thereby
enhancing a person’s ability to detect the psi-mediated in-
formation (Honorton, 1969, 1977). In order to test the hy-
pothesis that a reduction of sensory input itself facilitates
psi performance, investigators turned to the ganzfeld pro-
cedure (Braud, Wood, & Braud, 1975; Honorton & Harper,
1974;
Parker,
1975), a procedure
originally introduced
into experimental
psychology during the 1930s
to
test
propositions derived from Gestalt theory (Avant,
1965;
Metzger, 1930).
Like the dream studies, the psi ganzfeld procedure has
most often been used to test for telepathic communication
. between a sender and a receiver. The receiver is placed in
a
reclining
chair
in
an
acoustically-isolated
room.
Translucent ping-pong ball halves are taped over the eyes
and headphones are placed over the ears; a red floodlight
directed toward the eyes produces an undifferentiated vi-
sual field and white noise played through the headphones
produces an analogous auditory field.
It is this homoge-
neous perceptual environment that is called the Ganzfeld
(“total field”). In order to reduce internal somatic “noise,”
the receiver typically also undergoes a series of progres-
sive relaxation exercises at the beginning of the ganzfeld
period.
The sender is sequestered in a separate acoustically-
isolated room, and a visual stimulus (art print, photo-
graph, or brief videotaped sequence) is randomly selected
from a large pool of such stimuli to serve as the target for
the session. While the sender concentrates on the target,
the receiver provides a continuous verbal report of his or
her ongoing imagery and mentation, usually for about 30
minutes. At the completion of the ganzfeld period, the re-
ceiver is presented with several stimuli (usually four) and,
without knowing which stimulus was the target, is asked
to rate the degree to which each matches the imagery and
mentation experienced during the ganzfeld period. If the
receiver assigns the highest rating to the target stimulus,
it
is scored as a “hit." Thus, if the experiment employs
judging pools containing four stimuli (the target and three
“decoys” or control stimuli), then the hit rate expected by
chance is .25. The ratings can also be analyzed in other
ways;
for example, they can be converted
to ranks
or
standardized scores within each set and analyzed para-
metrically across sessions. And, as with the dream stud-
ies, the similarity ratings can also be made by outside
judges using transcripts of the
receiver’s mentation re-
port.
Meta-analyses of the Ganzfeld Database
In 1985 and 1986, the Journal of Parapsychology de-
voted two entire issues to a
critical examination of the
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ganzfeld database. The 1985 issue comprised two contri-
butions: (a) a meta-analysis and critique by Ray Hyman
(1985), a
cognitive
psychologist and
skeptical
critic
of
parapsychological
research; and
(b) a competing meta-
analysis and
rejoinder by
Charles Honorton
(1985),
a
parapsychologist and major contributor
to the ganzfeld
database. The 1986 issue contained four commentaries on
the Hyman-Honorton exchange, a joint communique by
Hyman and Honorton, and six additional commentaries
on the joint communique itself. We summarize the major
issues and conclusions here.
Replication Rates
By study. Hyman's meta-analysis covered 42 psi ganz-
feld studies reported in 34 separate reports written or
published from 1974 through 1981. One of the first prob-
lems he discovered in the database was multiple analysis.
As noted above, it is possible to calculate several indices of
psi performance in a ganzfeld experiment and, further, to
subject those indices to several kinds of statistical treat-
ment. Many investigators reported multiple indices or ap-
plied multiple statistical tests without adjusting the crite-
rion significance level for the number of tests conducted.
Worse, some may have “shopped” among the alternatives
until finding one that yielded a significantly successful
outcome. Honorton agreed that this was a problem.
Accordingly,
Honorton
applied
a
uniform
test on
a
common index across all studies from which the pertinent
datum could be extracted, regardless ofhow the investiga-
tors had analyzed the data in the original reports. He se-
lected the proportion of hits as the common index because
it could be calculated for the largest subset of studies: 28
of the 42 studies. The hit rate is also a conservative index
because it discards most of the rating information; a sec-
ond
place
ranking—a
“near
miss”—receives
no
more
credit than a last place ranking. Honorton then calculated
the exact binomial probability and its associated z score
for each study.
Of the 28 studies, 23 (82%) had positive z scores (p =
4.6 x 10—
exact binomial test with p = q = .5). Twelve of
the studies (43%) had z scores that were independently
significant at the 5% level (p = 3.5 x 10“9
, binomial test
with n = 28 studies, p =
.05, and q =
.95) and 7 of the
studies (25%) were independently significant at the 1%
level
(.p = 9.8 x
10-9
). The composite
Stouffer z score
across the 28 studies was 6.60 (p = 2.1 x 10- *-•*). 1 A more
conservative estimate of significance can be obtained by
including 10 additional studies that also used the relevant
judging procedure but did not report hit rates. If we as-
sign these studies a mean z score of zero, then the Stouffer
z across all 38 studies becomes 5.67 (p = 7.3 x ftX-9
).
Thus, whether one considers only the studies for which
the relevant information is available or includes a null es-
timate for the additional studies where the information is
not available, the aggregate results cannot reasonably be
attributed to chance. And by design, the cumulative out-
come reported here cannot be attributed to the inflation of
significance levels through multiple analysis.
By
laboratory. One
objection
to estimates
like those
above is that studies from a common laboratory are not
IStouffer’s z is computed by dividing the sum of the z scores for
the individual studies by the square root of the number of studies
(Rosenthal, 1978).
independent of one another (Parker, 1978). Thus it is pos-
sible for one or two investigators to be disproportionately
responsible for a high replication rate while other, inde-
pendent investigators are unable to obtain the effect.
The ganzfeld database is vulnerable to this possibility.
The 28 studies providing hit rate information were con-
ducted by investigators in 10 different laboratories. One
laboratory contributed nine of the studies; Honorton’s own
laboratory contributed
five; two other laboratories
con-
tributed three each; two contributed two each; and the
remaining four laboratories each contributed one. Thus
half of the studies were conducted by only two laborato-
ries, one of them Honorton’s own.
Accordingly, Honorton calculated a separate Stouffer z
score for each laboratory. Significantly positive outcomes
were reported by 6 of the 10 laboratories and the com-
bined result across laboratories yielded a z of 6.16 (p = 3.6
x 10“ 19
). Even
if all the studies conducted by the two
most prolific laboratories are discarded from the analysis,
the Stouffer z across the eight other laboratories remains
significant (z = 3.67,p = 1.2 x 10-4
). Four of these studies
are significant at the 1% level (p = 9.2 x 10“6
, binomial
test with n = 14 studies, p = .01, and q =
.99), and each
was contributed by a different laboratoiy.
Thus, even though the total number of laboratories in
this database is small, a majority of them have reported
significant studies, and the significance of the overall ef-
fect does not depend on just one or two of them.
Selective Reporting
In recent years, behavioral scientists have become
in-
creasingly aware of the “file-drawer” problem, the likeli-
hood that successful studies are more
likely to be pub-
lished than unsuccessful studies—which are more likely
to be consigned to the file drawers of their disappointed
investigators (Bozarth & Roberts, 1972; Sterling,
1959).
Parapsychologists were among the first to become sensi-
tive to the problem; and, in 1975, the Parapsychological
Association Council adopted a policy opposing the selec-
tive reporting of positive outcomes. As a consequence,
negative findings have been routinely reported at the As-
sociation’s meetings and in its affiliated publications for
almost two decades now. As we have already seen, more
than half of the ganzfeld studies included in the meta-
analysis yielded outcomes whose significance falls short of
the conventional .05 level.
There
is a variant of the selective reporting problem
which
arises from what Hyman (1985) has termed the
“retrospective study.” An investigator conducts a small set
of exploratory trials. If they yield null results, they remain
“exploratory” and never become part of the official record;
if they happen to yield positive results, they get defined as
a study after the fact and are submitted for publication. In
support of this possibility, Hyman notes that there are
more significant studies in the database with fewer than
trials than one would expect under the assumption
that, all other things being equal, statistical power should
increase with the square root of the sample size. Although
Honorton questions the assumption that “all other things”
are in
fact equal across the studies and disagrees with
Hyman’s particular statistical analysis, he does agree that
there is an apparent clustering of significant studies with
fewer
than
trials.
(Out
of
the
complete
ganzfeld
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database of 42 studies, 8 have fewer than 20 trials, and 6
of these report statistically significant results.)
Because
it
is impossible, by
definition,
to know how
many unknown
studies—exploratory or otherwise—are
languishing in file drawers somewhere, the major tool for
estimating the seriousness of selective reporting problems
has become some
variant
of Rosenthal’s
“file
drawer”
statistic, an estimate of how many unreported studies
with z scores of zero would be required to exactly cancel
out the significance of the known database (Rosenthal,
1979). For the 28 direct-hit ganzfeld studies alone, this es-
timate is 423 fugitive studies, a ratio of unreported-to-re-
ported studies of approximately 15 to
1. When
it is re-
called that a single ganzfeld session takes over an hour to
conduct,
it
is not
surprising that—despite
his concern
with
the
retrospective study problem—Hyman concurs
with Honorton and other participants in the published
debate that selective reporting problems cannot plausibly
account for the overall statistical significance of the psi
ganzfeld database (Hyman & Honorton, 1986).
Methodological Flaws
If the most frequent criticism of parapsychology is that
it haB not produced a replicable psi effect, the second most
frequent criticism is that many,
if not most, psi experi-
ments have
inadequate
controls and
procedural
safe-
guards. A frequent charge is that positive results emerge
primarily from: initial, poorly controlled studies and then
vanish as better controls and safeguards are introduced.
Fortunately, meta-analysis provides a vehicle for empir-
ically evaluating the extent to which methodological flaws
may have contributed
to
artifactual
positive outcomes
across a set of studies. First, ratings are assigned to each
study that index the degree to which particular method-
ological flaws are or are not present; these ratings are
then correlated with the studies’ outcomes. Large positive
correlations constitute evidence that the observed effect
may be artifactual.
In
psi
research,
the most fatal flaws are those that
might permit a subject to obtain the target information in
normal sensory fashion, either inadvertently or through
deliberate cheating. This is called the problem of sensory
leakage. Another potentially serious flaw is inadequate
randomization of target selection.
Sensory leakage. Because the ganzfeld is itself a percep-
tual isolation procedure, it goes a long way toward elimi-
nating potential sensory leakage during the ganzfeld por-
tion of the session. There are, however, potential channels
of sensory leakage following the ganzfeld period. For ex-
ample, if the experimenter who interacts with the receiver
knows the identity of the target, he or she could bias the
receiver’s similarity ratings in favor of correct identifica-
tion. Only one study in the database contained this flaw, a
study in which subjects actually performed slightly below
chance expectation. Second, if the stimulus set given to
the receiver forjudging contains the actual physical target
handled by the sender during the sending period, there
might be cues (e.g., fingerprints, smudges, or temperature
differences) that could differentiate the target from the
2A 1980 survey of parapsychologists uncovered only 19 com-
pleted but
unreported
ganzfeld
studies. Seven
of these had
achieved
significantly positive
results,
a proportion
(.37) very
similar to the proportion of independently significant studies in
the meta-analysis (.43) (Blackmore, 1980).
decoys. Moreover, the process of transferring the stimulus
materials to the receiver’s room itself opens up other po-
tential channels of sensory leakage. Although contempo-
rary ganzfeld studies eliminate both of these possibilities
by using duplicate stimulus sets, some of the earlier stud-
ies' did not.
Independent analyses by Hyman and Honorton agreed
that there was no correlation between inadequacies of se-
curity against sensory leakage and study outcome. Honor-
ton further reported that if studies that failed to use du-
plicate stimulus sets were discarded from the
analysis,
the remaining studies are still highly significant (Stouffer
* = 4.35, p = 6.8 x 1CT6
)
Randomization. In many psi experiments, the issue of
target randomization is critical because systematic pat-
terns in inadequately randomized target sequences might
be detected by subjects during a session or might match
subjects’ pre-existing response biases. In a ganzfeld study,
however, randomization is a much less critical issue be-
cause only one target is selected during the session and
most subjects serve in only one session. The primary con-
cern is simply that all targets be sampled about equally
over the course of the study. Similar considerations gov-
ern the second randomization, which takes place after the
ganzfeld period and determines the sequence in which the
target and decoys are presented to the receiver (or exter-
nal judge) for judging.
Nevertheless, Hyman and Honorton disagreed over the
findings here. Hyman claimed there was a correlation be-
tween flaws of randomization and study qutcome; Honor-
ton claimed there was not. The sources of this disagree-
ment were in conflicting definitions of flaw categories, in
the coding and assignment of flaw ratings to individual
studies, and in the subsequent
statistical treatment of
those ratings.
Unfortunately, there have been no ratings of flaws by
independent raters who were blind to the studies’ out-
comes (Morris, 1991). Nevertheless, none of the contribu-
tors to the subsequent debate concurred with Hyman’s
conclusion
whereas
four
nonparapsychologists—two
statisticians and two psychologists—explicitly concurred
with Honorton’s conclusion (Harris & Rosenthal,
1988b;
Saunders,
1985; Utts,
1991a). For example, Harris and
Rosenthal (one of the pioneers in the use of meta-analysis
in psychology) used Hyman’s own flaw ratings and failed
to find any significant relationships between flaws and
study outcomes in each of two separate analyses: “Our
analysis of the effects of flaws on study outcome lends no
support to the hypothesis that Ganzfeld research results
are
a
significant function of the set of flaw variables”
(1988b, p. 3). (For a more recent exchange over Hyman’s
analysis,
see Hyman
(1991),
Utts
(1991a),
and
Utts
(1991b).)
Effect Size
Some critics of parapsychology have argued that even if
current
laboratory-produced
psi
effects turn out
to be
replicable and non-artifactual, they are too small to be of
theoretical interest or practical importance. We do not be-
lieve this to be the case for the psi ganzfeld effect.
In psi ganzfeld studies, the hit rate
itself provides a
straightforward descriptive measure of effect size, but this
cannot be compared directly across studies because they
do not all use a four-stimulus judging set and, hence, do
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