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Parapsychology >> Subliminal Persuasion
signal detection theory, research controversy, sensory impressions, subliminal perception

What is Subliminal Influence?

Author: Todd I. Stark

© 2/1999 ToddStark@AOL.COM

The term subliminal
is technically archaic, though it is still in common use.   The problem
is that it is hopelessly bound to the concept of a well-defined sensory threshold, a
concept made obsolete by the introduction of signal detection theory into psychology HREF="/perl/ and Swets, 1967 Signal Detection">(Green & Swets, 1967). 

face="Georgia" size="2">We continue to use this term, (like the term "trance" in
hypnosis), because it is so deeply ingrained in the minds of both scientists and the
public.  The term itself means "below the threshold," but there is no
single clear threshold to sensory perception.  There are a vast array of different
sensory features detected and processed before being brought to awareness, with the help
of attention.  This makes for a great deal of flexibility in how and what we
integrate when we bring sensory impressions into awareness. 

In technical usage, we consider a stimulus subliminal
if  it is too faint, too brief, or otherwise does not stimulate our senses
sufficiently to cause us to notice it, yet influences subsequent tests in some way

However, a more technically accurate term for this would be HREF="Marginal.html">marginally perceptible.  

The popular meaning of the term subliminal is anything
that influences us from outside of our awareness.

Interest in subliminal influence in modern times goes
back to sensory physiologist HREF="/perl/, Otto (1917/1960). The relationship">Otto Poetzl in
the early 1900's, who studied the effect of rapidly flashed pictures on dreams.  In
the 1950's the invention of the tachistoscope for more rapidly flashing images spurred a
renewed research interest in subliminal perception, the fate of stimuli not noticed. 
Originally a sensory curiosity, it was growing into both a research controversy and a
public controversy.  

The story of "subliminal persuasion"
begins with the report of market research consultant HREF="/perl/ Vicary article">James Vicary that he could influence the
buying behavior of movie patrons by flashing invisible messages on the screen.  In a
climate prepared by the dire view of social critic HREF="/perl/, Vance, (1957). The Hidden Persuaders,">Vance Packard,
this created an amazingly widespead and enduring fear of unseen messages in media.
  This has evolved into fear of movies, television, magazine pictures, embedded
messages in Muzak in stores, in computer software and even fear of backward-played satanic
messages in music.

Packard himself seems to have been mostly concerned about
the use of psychoanalysts, or "depth men" by advertisers to craft carefully
symbolic messages in advertisements.  This created still more sources of  fear,
such as the neverending rumors of hidden sexual symbols in
children's movies. 

The story has an offshoot, into the lucrative realm
of audiotapes that are supposed to help us reprogram our mind effortlessly and
unconsciously with self-help messages.  Similar subliminal influence is also claimed
to help would-be seducers win hearts and minds of their quarry. 

The term subliminal is commonly used to mean a number of
different kinds of hidden messages. 

  • Images of carefully contrived social situations and
    suggestive body language

  • Blatant or artistically concealed symbols suggestive of
    powerful instinctual drives

  • Faint or briefly flashed words or images

  • Acoustically masked or backward messages in music

  • Metaphor and other "hypnotic" language patterns

Of these various kinds of "subliminal"
influence, psychologists usually refer only to the briefly flashed words or images, and
sometimes the acoustic masking, when they talk about marginal or subliminal
perception.  Those are the stimuli used in the subliminal priming experiments
that produce temporary, weak psychological effects.

In other words, the experimenters most
actively  involved in  research into subliminal priming generally agree that it
exists, but that it consists of relatively weak and fleeting effects of primarily
theoretical interest.  (Merikle,
in press)
This is certainly true of
unconscous semantic priming.

Several widely-read authors, particularly HREF="/perl/ (1973). Subliminal Seduction">Wilson Bryan Key
brought the term subliminal into wider public awareness.  Most of this
literature is a  warning that advertisers are capable of influencing us through
hidden messages, and actively do so, with malicious intent.   The warning refers
to not only what the psychologists would call subliminal priming, but also a variety of
other kinds of sneaky persuasion tactics popularly associated with the term subliminal.

Following the lead of HREF="/perl/ (1973). Subliminal Seduction">Key, HREF="/perl/, Vance, (1957). The Hidden Persuaders,">Vance Packard
before him, and others in their genre, the term subliminal is more commonly used to
refer to any influence on us that we don't notice.  In addition to the weak
stimuli used by researchers, this also includes things like hidden images in pictures, the
crafting of scenes for emotional content, playing sounds backwards, metaphorical or
otherwise embedded symbolism in language, the use of visual symbols to invoke instinctual
drives, and so on. 

Whether any of these things has an
"unconscious" effect is a matter of definition, but whether they are effective
is an empirical matter.  Lumping them all together into one category
with too faint and t
oo brief messages used in
cognitive science experiments makes it virtually impossible to sort out varied things like
social psychological influence, suggestion, emotional appeal, associative conditioning,
and preconscious processing. 

Subliminal semantic priming is the
effect of briefly flashed words on categorizing subsequent words in a forced choice test.
It only lasts about 100 milliseconds and does not carry over from one trial to the next in
experiments.  (Greenwald
et al, 1996)

Subliminal perceptual priming is the effect
of a briefly flashed picture on our preferences in a forced choice test, and is more
robust.  This is better known as the "mere exposure effect."  HREF="/perl/,1980">(Zajonc, 1980).  Variations of the mere exposure
effect have been demonstrated to activate emotional centers of the brain, particularly the
amygdala, without awareness.  HREF="/perl/ et al on emotional activation of amygdala">(Whalen et al, 1998).

This probably has some relevance to the "classical
conditioning" of emotional memories without awareness.   This begins to
enter into the realm of something that could be crafted into an effective propaganda tool,
especially as a reinforcer. 

psychodynamic activation
is one of the oldest methods, and the most
intriguing.  Subliminal stimuli can enter into dreams and waking imagery in a
transformed way (Shevrin,1986),
influence later recall and perception (Shevrin,
, and most remarkably even influence our social functioning. HREF="/perl/, 1976">(Silverman, 1976, HREF="/perl/, 1978">1978).    However, it is also the
most difficult to demonstrate, presumably  because it is the most vulnerable to the
individual differences and the psychological state of the recipient, and the vagueries of
subjective interpretation of results. 

The most effective techniques in practice involve
both conscious and unconscious elements, coordinated to appeal to our
emotions and exploit our natural information processing and aesthetic biases, as well as
lead our conscious thinking processes in a desired way. 

Becoming aware of subliminal stimuli generally
negates or reduces their influence, in both the mere exposure and psychodynamic
experiments.  The combination of conscious and unconscious elements must be carefully
coordinated, but not duplictated (unconscious elements should not be made conscious).

The reason why this approach is most effective,
compared to one emphasizing or relying on hidden messages, is that hidden messages can
influence our thinking and feeling, but not directly cause behavior, at least not by any
yet known effect. 

The known subliminal effects influence behavior
indireectly, if at all, by influencing perception, thinking and feeling.  Conscious
thinking organizes and triggers most behavior, even though aspects of behavior are
unconscious, such as the details of movements and the expression of much of nonverbal

Hypnosis research has shown that effective
illusions and compulsions cab be created through suggestion under some conditions with
some people, without conscious awareness of the exact source. HREF="/perl/, J.F. (1995). Hypnosis, memory, and"> (Kihlstrom, 1995) 

These hypnotic suggestion effects are limited by
the expectations of the subject, their relationship with the hypnotist,  and the
demand characteristics of the situation.  HREF="/perl/, M.T., & Evans, F.J. (1965). Social control">(Orne &
Evans, 1965).  The more the subject expects to be controlled, and the greater
their rapport or sense of cooperation with the hypnotist, the more involuntary they
perceive their response.  HREF="/perl/, Nash, Rhue, Involuntariness factors">(Lynn, Nash, Rhue, et. al.,

It is the degree to which subliminal messages could
produce a similar kind of dissociated control that is at the heart of the most virulent
potential threat of subliminal persuasion.  Without the relationship and expectancy
factors that make hypnotic suggestion effective, it is difficult to see how the comparison
can be meaningfully made.  

Unless they are tailored to the individual, there
is no convincing evidence of any more elaborate effect from purely preconscious processing
of hidden messages, or even that they are worth persuing as an aid to advertising.  HREF="/perl/, Joel (1987). Why Marketing Should Quit"> (Saegert, 1987). 

Achieving this kind of effect through a combination of
subliminal messaging and hypnotic techniques remains a theoretical possibility under some
conditions.   At issue is the problem of creating the cooperative mindset needed
for hypnosis, creating the expectancy that we can  be controlled, and  the
differences in the way individuals respond to hypnotic suggestion.

The threat of subliminal influence seems limited at this
time to relatively weak reinforcement of conscious messages, but the combination of such
effects can be difficult to determine.  A message employing subliminal techniques,
like any message, can often have unanticipated effects on the listener depending on their
own psychological needs and mindset.

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