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e. See "Richard George Medhurst 1920-1971," an obituary by Mary Rose Bar-
rington J.S.P.R. 46(1971), 124-6.
f. Some years later I was reminded of this remark by Charles Honorton. By
then claims were confidently being made that techniques such as the ganzfeld and
remote-viewing were producing success rates approaching 50 percent. Unfor-
tunately, success was still limited to a few favored experimenters. My students at
Edinburgh were no more successful using these new techniques than they had been
with traditional methods of testing for ESP.
g. At that time Walter J. Levy at the Institute for Parapsychology was still
producing an unprecedented string of successes with his gerbils and other
animal subjects who were required to influence a random-event generator in
order to obtain some reward. The crash came in the summer of 1974 when Levy
was detected by his colleagues fraudulently manipulating the computer.
h. That is, Sir Alec Douglas-Home. Recently, however, Hall (1984) has
raised serious doubts as to whether Daniel Home was, in fact, related to the
Earls of Home. It was thought that his father was an illegitimate son of the 14th
Earl. D.D. Home, for understandable reasons, sought to foster belief in a rela-
tionship by adopting, as his middle name, "Dunglas." In the Currie register
he is listed simply as Daniel Home.
The Subliminal and the Extrasensory
What follows was my contribution to an international conference at
Amsterdam in August 1972 to which I had been invited by the Parapsychology
Foundation of New York. The theme of the conference was "Parapsychology
and the Sciences" (Parapsychology Foundation 1974) but the one science about
which I had any qualifications to speak was, of course, psychology and it was
the experimental study of visual perception that had been my special concern.
While reviewing Norman Dixon's Subliminal Perception (1971) for a
psychology journal, I had been struck by the implications of his findings for
parapsychology. At that time there had as yet been no empirical research link-
ing subliminal with extrasensory perception but since then there have been a
fair number of such studies (Roney-Dougal 1986; Nash 1986). Professor Dixon,
himself, is one of the few distinguished British psychologists who has been con-
sistently friendly to parapsychology. He has himself speculated since then on
the relationship that I here discuss (Dixon 1979; 1987) and provided valuable
assistance to Serena Roney-Dougal when she was working on her doctoral
dissertation on this topic (Roney-Dougal 1987).
From the earliest days of parapsychology it has generally been
acknowledged that, whatever part of us is responsible for mediating extrasen-
sory information, it is not the part that we associate with our conscious or ra-
tional intellect. The concept of the unconscious became a commonplace of
nineteenth-century thought long before it reached fruition in the work of
Freud and, as can be seen from the writings of Frederic Myers or of William
James, the phenomena of the séance-room played a part in its development
second only to those of the clinic. Indeed both depth psychology and para-
psychology can trace a common ancestor in the mesmerist movement of the
early 19th century. But, although parapsychologists have never ceased to bor-
row freely from the treasure house of psychoanalytic ideas, these ideas for the
most part were lacking the rigorous experimental basis that was necessary if
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they were to be integrated into an experimental parapsychology. There was,
however, one concept of a psychodynamic nature that right from the start was
firmly grounded in laboratory experiments rather than in clinical observations.
Such was the concept of subliminal perception. In this paper I want to consider
what implications, if any, the findings on subliminal perception may have for
the study of extrasensory perception. Is there, in short, a useful parallel to be
drawn between SP (Subliminal Perception) and ESP (if you will allow me this
play on words or on letters)?
My interest in this question arose from reading a recent book by Dr. Nor-
man Dixon of University College, London, entitled Subliminal Perception
(Dixon 1971), which I had been asked to review. Dixon, I should say, is the
foremost authority on this topic in my country and his extensive researches
have done as much as anything to establish, on a secure scientific footing, a
concept that not long ago was still being treated with suspicion, if not derision.
It is noteworthy that Dixon subtitles his book "The Nature of a Controversy."
As I read the book I was struck repeatedly by the fact that what he had to say
about SP seemed to apply equally to ESP, and the analogy seemed the more
telling inasmuch as Dixon nowhere makes it explicit. In fact, though I gather
that he is open-minded on the question, he has no special interest in and no
definite views about paranormal phenomena. To make my intentions quite
clear from the beginning, however, let me declare straight away how far I pro-
pose to press my analogy and what I take to be its necessary limits.
Obviously, no amount of knowledge that we may acquire about the work-
ing of SP will account for the existence of ESP. There is, after all, an absolute
difference between a stimulus of very low intensity and a target that, being
isolated from all sensory contact with the subject, is, in effect, a stimulus of
zero intensity. Thus, whereas Dixon devotes a considerable portion of the book
to arguing that there is nothing in the physiology of the brain or nervous
system that should preclude the existence of SP, this, of course, is just what
we cannot argue with respect to ESP. For, whether or not one believes that ESP
may eventually be assimilated within the framework of an expanded physics
and physiology, the obdurate fact that we have to face is that, as of now, the
problem of how a subject might acquire information about an extrasensory
target remains a total and absolute mystery.
Hence my analogy can begin only at the point at which we may suppose
that, somehow or other, the target has been apprehended. But, from that
point on, what happens to the information, how it is decoded and processed,
how the transition is effected from unconscious to conscious awareness, to
questions of this order, Dixon's evidence and interpretations are, I maintain,
relevant and illuminating. Following Dixon I am going to assume that we all
possess two distinct cognitive systems, each mediated by its own set of brain
mechanisms. There is, on the one hand, a primary system whose main function
is to subserve selective attention and logical thought. This always involves
consciousness, a relatively high state of arousal and the mediation of the
ascending reticular activating system of the brain. There is, on the other hand
a secondary system that may operate in the absence of consciousness, i
associated with a relatively low state of arousal and is mediated by limbic and
midbrain mechanisms. The function of this secondary system is less easy to
define but it appears to be a kind of cognitive safety valve that allows us to ac
cess to a wide range of information that would otherwise be entirely excluded
by the inhibitory mechanisms of the primary system. It is, we may suppose
involved in dreaming, in free-association and spontaneous imagery, in in
tuitive thinking and, no doubt, in those "games of the underground" tha
Koestler has described for us so graphically in connection with the bisociativ
leaps of his creative thinkers (Koestler 1964). It is to this secondaty system tha
Dixon ascribes our capacity for subliminal perception and it is my thesis tha
it is this system that is involved in the psi process.
In the classical or Cartesian tradition of European philosophy "mind" an
"consciousness" are interchangeable concepts so that events or processes the
are not conscious cannot be mental and must therefore be physical. Accordin
to a very different philosophical tradition, however, of which Bergson may her
be taken as representative (Bergson 1911), our conscious self is nothing moi
than the residue that remains when awareness has been filtered of everythin
except that which pertains to the individuals' biological needs. Mind itself
conceived of as being potentially omniscient and all-embracing but this un
versality is sacrificed, according to Bergson, in the ego-centered struggle fr
survival. Now, just as Dixon regards SP as a compromise between the restricti
demands of selective attention and the need for the organism to monitor
much wider range of stimuli, so I am going to suggest ESP may be regarde
as a compromise between the exclusiveness of the Bergsonian filter and th.
cosmic capacity of mind to transcend the limits of the senses. Both ph
nomena, however, seem to be of marginal importance in everyday life relati
to normal perception.
So much for the general viewpoint from which I am approaching th
question. Now let us take a look at some of the facts and findings that resear
on subliminal perception has uncovered. First we should note that SP is
special case of the more general phenomenon of discrimination without awar
ness. No one can deny that we constantly make all kinds of adaptive discrin
nations without being aware of what we are doing. Indeed, the more skill
we are at any given activity the less we need to be aware of the details of o
performance. What is peculiar about SP is that in this case the cues are so feel
physically that they could never reach the threshold for conscious recogniti
however hard we might try attending to them. Now it is one of the key pois
of Dixon's argument that SP is not just a dilute form of ordinary perceptic
Provided (a) the stimulus is well and truly below recognition threshold and (
that it still retains any efficacy at all, then it will be dealt with by the subj.
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in quite a different way from one that is strong enough to elicit a conscious
sensation.
This is best illustrated when the stimulus in question is a familiar
word.
Suppose your subject is shown a word and asked to report, as best he can,
what he sees. Then, provided the word is visible at all, however faintly or
however briefly, the subject's response is likely to bear at least some structural
resemblance to the actual word. But if that word is exposed at such a low inten-
sity or for such a minute duration that it is in effect invisible, so that the subject
can do no more than guess at it, as if it were an ESP target, then the evidence
suggests that the response is unlikely to have any structural resemblance to the
stimulus word but may very well have a semantic relationship. Sometimes the
semantic processing involved, which, of course, all takes place at a purely un-
conscious level, seems to involve a rather elaborate symbolic transformation.
This is particularly so if the word has some emotional or sexual significance for
the subject. Dixon himself gives several examples of such responses that show
a distinctly Freudian character. This qualitative shift in the response, which oc-
curs when the intensity of the stimulus falls well below recognition threshold,
is explained by supposing that it is then that our secondary system takes over
from the primary system. Dixon further points out that subliminal perception
is more likely to occur when the subject is in a relaxed or passive state, as when
he is made to recline on a couch; in other words he functions best in a low state
of arousal.
A special kind of subliminal perception that has long intrigued in-
vestigators is the so-called "Poetzl Phenomenon," after the Austrian neurolo-
gist, Otto Poetzl, who first drew attention to it in 1917 (Poetzl et al. 1960).
Briefly, what he found was that if his subjects were shown a picture in a tachis-
toscope for about a 10m.s. duration, so that it was impossible for them to
discern more than the most fragmentary features of the picture, much of the
remaining content could still be recovered, even if in a somewhat disguised or
symbolic form, if the subject was later asked to recall his dreams of the subse-
quent night. Although, needless to say, the validity of this phenomenon has
been strongly challenged, there have also been some good confirmations of it
from recent experiments using very carefully controlled experimental designs
(Dixon 1971). However, recent work has also shown that the effect is not
limited to dreams. It appears to be sufficient if, after being presented with the
picture in the tachistoscope, the subject is merely asked to relax and describe
any spontaneous images that may then emerge into consciousness. It surely re-
quires no special pleading to find a parallel here with the Maimonides situation
(Ullman et al. 1970). The Maimonides experiments exploit the same oblique
approach in demonstrating an ESP effect in the way the picture target in-
fluences the dream imagery of the sleeping subject. Moreover, in this case, too,
hypnotic dreams and waking imagery can be used as well as nocturnal dreams
(Krippner 1968). In general wherever free-response techniques have been use
to test for ESP, as for example in token-object reading, the symbolic distortion.
noted by Dixon when testing for SP are liable to occur.
One of the main points of departure for the modern study of SP was
series of observations arising out of the work of a group of experiment:
psychologists in the late 1940s who came to be known as the "New Look Schoc
of Perception." Leo Postman and Jerome Bruner, two of its leading exponent:
claimed that, in general, recognition thresholds for emotive words differe
from those for neutral words. If the threshold was raised, i.e., recognition too
longer, as might be expected when the word had unpleasant, alarming c
distressing connotations for the subject, then one had a case of "perceptu:
defense." If, on the contrary, the threshold was lowered, i.e., recognitio
became easier, as might be expected if the word had positive connotations fc
the subject, then one had a case of perceptual sensitization. Actually, whethe
the threshold for a given word is raised or lowered relative to a neutral wor
may depend as much on the personality of the subject as upon the character
of the word, so that a perceptually vigilant subject may be expected to respon.
sooner even to a distressing signal. The important point, however, is the ex
istence of this differential effect as between emotionally charged stimulu
words and neutral words.
A particular experiment by E. McGinnies (McGinnies 1949) in 194
sparked off what may well qualify as the longest specific controversy in th
history of experimental psychology (Brown 1961). In this experiment he ex
posed a series of words in a tachistoscope in which the critical items were sc
called "taboo" words, i.e., words with a strong sexual flavor like "whore" c
"rape." He duly reported that these critical items required longer exposure t
reach recognition than control items of the same length. The interpretation
was that a censorship was operating at an unconscious level to prevent iden
tification of the forbidden words for as long as possible. Thus the concept o
"perceptual defense" was postulated as a direct analogue to the Freudian con
cept of repression in the field of memory phenomena. Of course McGinnie:
experiment was far too full of flaws to establish the validity of such a concep
of its own accord. All kinds of reasons were put forward by critics to accoun
for the fact that the taboo words took longer to recognize - subjects might hav
hesitated before pronouncing the words until they were quite sure, or th
words might be less common than the control words, or perhaps less expecter
in the laboratory situation. Evidence and arguments both for and against th
reality of perceptual defense continued to pile up during the 1950s and 1960
as supporters of the concept strove to meet each new criticism and counter
explanation. Eventually, however, though there still are doubters and
waverers, perceptual defense does appear to have been vindicated as a genuin
manifestation of the unconscious.
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kind we owe to Dixon, or to A.G. Worthington, a Canadian psychologist, the
subject never, at any time during the experiment, suspects that there are any
words involved, let alone that some of them may be obscene. All the experi-
menter looks for is whether the critical words will raise the recognition
threshold relative to the control words with respect to some quite neutral
stimulus such as a patch of light. Thus, in Dixon's set-up, the critical word is
exposed continuously to one eye only and at a level well below that at which
he could be aware that there is any kind of stimulus present. At the same time
the other eye is presented with a visible spot of light whose intensity the subject
himself can control. His instructions are to keep the spot of light from disap-
pearing altogether while at the same time not to let it exceed in brightness a
second spot of light that surrounds it. Dixon duly found that the mere presence
of the taboo word was in itself sufficient to raise the threshold-setting for the
spot of light; the implication being that resistance to seeing the taboo word
raised the general threshold for form discrimination.
In an experiment of this kind which one of my own students carried out
this year (Gregor 1972), the subject was required only to indicate when a cer-
tain luminous rectangle was visible against a uniform luminous background.
Unbeknown to the subject the luminous rectangle was in fact a slide containing
a word, either a sexually suggestive word or a carefully matched neutral word.
Although great care was taken to guard against artifacts-for example the ex-
perimenter himself did not know which slide was being used on which trial - it
duly transpired that the mean intensity necessary to discriminate the rectangle
against its background was significantly greater when the word it contained was
of an obscene nature than when it had no such emotional connotation.
Findings like these strike one as so bizarre, from a commonsense point of
view, that one may be forgiven for wondering whether ESP might not be a
more straightforward explanation for the results than one in terms of SP. Ac-
tually, Dixon himself has told me that one cannot rule this out as a hypo-
thetical possibility since few experimenters have bothered to control for an ESP
effect. Not that this would be difficult, all one would need would be for the
stimulus to be present, as a target, on certain trials but completely screened
from the subject. I do not think Dixon takes this possibility very seriously or
he would already have done something about it. Neither do I take it seriously
for that matter. Nevertheless, it is a nice stroke of irony that, for once, we
should be discussing ESP as a potential explanation of an alleged case of SP in-
stead of, as so often, SP as an explanation for an alleged case of ESP.
threatening or disturbing nature; negative scoring is more likely to occur if, for
some reason, the subject is feeling anxious at the time or is acting under stress.
Nevertheless, given that we all tend to be apprehensive about anything
paranormal, that we instinctively recoil from anything that threatens to
penetrate our safe Bergsonian filters, it becomes understandable that we
sometimes consciously deny what our unconscious, so to speak, already knows.
For methodological reasons, however, it is difficult to compare psi-missing at
all directly with perceptual defense since the former can be clearly demon-
strated only by using quantitative experiments of the forced-choice variety
whereas the latter rely on qualitative free-response tests.ª
A type of perceptual defense that has been studied exhaustively in
Sweden is that which is observed in the so-called "Defense Mechanism Test"
designed by the Swedish psychologist Ulf Kragh (Kragh et al. 1970). This test
uses as a stimulus a TAT type of picture that invariably contains one threaten-
ing figure and one figure who is being threatened. A picture of this sort is then
exposed in a tachistoscope at successive trials of increasing duration starting at
a subliminal level, progressing through stages of preconscious recognition and
ending when the entire picture is clearly visible. The assumption behind it is
that an anxious subject will postpone for as long as possible acknowledging the
threatening figure that he will contrive to see in various innocuous ways. Mar-
tin Johnson, a parapsychologist and a colleague of Kragh's at Lund University,
using the Defense Mechanism Test (DMT) as a measure of anxiety, was able to
demonstrate a very significant correlation between the subject's score on the
DMT and his ESP score on a standard test of clairvoyance (his DMT protocols
were of course scored blind, i.e., in ignorance of his ESP scores). In general the
more anxious subject tended to be a psi-misser and the less anxious subject
tended to be a psi-hitter (Johnson et al. 1967).
Philosophers who write about parapsychology like to point out that ESP
is a misnomer, that really ESP is not a species of perception at all, or even of
cognition, since the typical ESP test is assessed solely according to the propor-
tion of guesses that coincide with the targets even though the subject himself
cannot distinguish in any way between his correct and his incorrect guesses.
This objection, however, stems from adopting the classic empiricist assump-
tion that we cannot know anything unless we are consciously aware of knowing
it. But it is precisely such an assumption that is challenged by the whole body
of evidence that Dixon brings to our notice. Consider modern signal-detection
theory as it has been developed by J.A. Swets and others as a branch of
decision-making theory (Swets 1964). Here the concept of a conscious recogni-
tion threshold is abandoned entirely. The subject is asked simply to guess
whether the signal in question is on or off for a given trial. Much of the time
the subject behaves in the same sort of way as an ESP subject, that is to say he
goes on guessing to oblige the experimenter but is not conscious either of the
The acknowledgment of perceptual defense as a genuine psychological
phenomenon should make it that much easier for us to accept the concept of
"psi-missing" as a parapsychological phenomenon. For the point about percep-
tual defense is that it implies the possibility of identifying a stimulus at an un-
conscious level in order to prevent its recognition at a conscious level. Now it
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be shown to be a direct mathematical function of the intensity of the stimulus
starting at the baseline of chance expectation, when the stimulus is at some
very low level of intensity, and climbing to 100 percent accuracy when the in-
tensity reaches some optimal level. Of course, somewhere along this con-
tinuum consciousness must supervene but from the standpoint of signal detec-
tion theory, which is behavioristic and operationist in its approach, this is quite
immaterial.
Ultimately what terms we choose to employ is always a question of seman-
tics and if a philosopher wants to insist that perception implies conscious
perception he is free to do so and can no doubt adduce good precedents for
his usage. The point I want to make here, however, is that the modern
psychophysical study of sensation and perception provides us with a good
analogue for describing extrasensory perception. The typical card-guessing
demonstration of ESP corresponds to the subliminal zone of the perceptual
continuum whereas an accurate clairvoyant ascertainment of pictures, objects
and scenes, such as is occasionally reported with certain exceptional sensitives,
corresponds to the superliminal zone. That, subjectively, there is no difference
between ESP guesswork and subliminal guesswork was shown in an experiment
that J.G. Miller published in 1940 (Miller 1940). He told his subjects that the
task was one of telepathy and that they were to gaze into a mirror, as if into
a crystal ball, and try imagining certain geometric figures that he was going to
try and transmit to them. Actually, he projected very faint real images of the
figures onto the back of the semitransparent mirror and the subjects duly
scored well above the chance level but, and this is the point I wish to bring
out, none of them suspected this ruse and all were surprised to learn that it
was not after all a genuine test of telepathy.
Finally, are there any practical implications to be derived from the work
on SP for research on ESP? One enticing possibility worth mentioning is that
of using an SP set-up in order to disguise a test of ESP. The idea has gained
currency lately that subjects perform better when they are unaware that they
are using their ESP. For example, some success has been reported using an
ostensible test of memory. Items on which the subject recalled one of the
wrong alternative answers were analyzed to see whether these corresponded
significantly with the alternatives which the experimenter arbitrarily desig-
nated as being the correct ESP target (Stanford 1971). It would not be difficult
at all from a practical point of view to reverse J.G. Miller's procedure and make
the subject think he was using his SP while in fact he was required to use his
ESP. There is, in fact, one experiment in the literature which I have come across
which does use this stratagem. This was an experiment by Jule Eisenbud pub-
lished in 1965 (Eisenbud 1965). He presented the numerals 2, 3 or 4 in a tachis-
toscope and the subject had to guess at each trial which of these three different
numerals had just been presented. On the critical runs, however, the same con-
stant stimulus, consisting of an amalgam of all three numerals, was presented
at every trial. Meanwhile, in the next room, an agent was synchronously watch-
ing a series composed of the numerals 2, 3 or 4 being flashed on a screen at
superliminal durations, the idea being to influence the subject's responses. Un-
fortunately, however, this ingenious idea did not work and no significant scores
were found on these critical runs, nor did it make any difference on the
ordinary runs whether an agent saw the stimuli or not.
There are, however, other ways of combining the subliminal and the ex-
trasensory that are worth trying. Here again Martin Johnson has been breaking
new ground with promising results (Johnson 1972). In an experiment, which
he has recently completed, he exposed his words subliminally but these words
were in the Finnish language so that any effects that they might have on the
responses of his Dutch subjects would have to be due to ESP over and above
any SP . It has also been suggested that, in a telepathic experiment, it is the
agent who should be presented with the targets on a subliminal basis. The idea
being that if it is indeed our unconscious that mediates the information, the
best results should be expected if the target directly enters the unconscious of
the agent. But, as yet, I have come across no actual accounts of experiments
using this procedure. Lastly, as I have already suggested, I hope the time wil:
come when experimental psychologists will have sufficient respect for the ESF
hypothesis to take the precaution of always introducing a set of ESP contre
trials in any future experiment on SP. It is not, however, my main concern ir
this paper to suggest how SP might be exploited in parapsychological research
My concern has been rather to consider how the advances that have been made
in our knowledge of subliminal processes, both on the psychodynamic and of
the physiological fronts, might contribute to advancing our knowledge of ps
processes.
Note
a. This was a mistake, as I later discovered thanks to Michael Thalbourne.
a ranking procedure is used in connection with some free-response target, as w.
the case in Thalbourne's own experiment on the paranormal reproduction of targ
drawings (Thalbourne 1981), then it is perfectly possible to demonstrate p:
missing.
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