HOW TO STUDY SUBLIMINAL MOVIE ADVERTISING
How to Build and Use a Tachistoscope
Robert S. Owen, CET, Ph.D.
Imagine the power of an advertiser who could put persuasive thoughts
into your mind without your conscious awareness! This is the idea
behind so-called "subliminal" advertising. According to some popular
accounts, movie theaters can sneak frames into the move that flash, "eat
popcorn," and the audience, supposedly unaware of having read this message,
will comply and buy more popcorn. The idea is that the message is
displayed for such a short period of time that the viewer does not have
time to consciously process it, and so is therefore not consciously aware
of having ever seen the message. According to proponents of this
idea, the viewer will nonetheless process the message at some level below
consciousness and thereby act upon it.
At first blush, this notion sounds very possible. After all, a
great proportion of our mental processes and subsequent behaviors happen
at a level that is below our level of awareness, even though these can
be consciously controlled: breathing, eye blinking, scratching a nose.
Have you ever been in a crowded room at a noisy party? Imagine that
you are involved in a conversation with a few friends, totally unaware
of what is being said in the conversations of dozens of groups around you.
Then you suddenly hear your name mentioned in a conversation three groups
away, and your heart steps up its pace just a little as you wonder what
they were saying about you! Ahah - here is solid evidence that we
do indeed process information at a level that is below our everyday levels
of consciousness, and that this information is being monitored in a way
that can immediately affect our conscious thoughts and behavior.
(This is called the coctail party phenomenon.)
However, if it really is possible to unconsciously influence people's
thoughts and behaviors in adverising, the word would certainly be out and
every advertiser would be doing it. Consultants who know how to do
this stuff would be making lots of money giving seminars on how to do it.
Indeed, why give seminars at all - why not just directly tap that unconscious
part of our brain and directly feed the information into memory?
The reason is that the multiple ways that our brain processes information
is not so simple, and we appear to have a lot of different kinds of processors
and pre-processors. For example, there is some pre-processing that
filters out multiple conversations at a party as a way to keep our main
processor (consciousness) from becoming overloaded with information.
The pre-processor is too small to hold very much, so it immediately flushes
apparently useless information into a shredder. Any useful piece
of information, such as the mention of our name, is passed along, but we
cannot recall any other contextual information, no matter how hard we try,
because it has already been flushed and shredded.
We cannot find any practical evidence that "subliminal" advertising
works, and yet we do know that pre-conscious processing systems exist.
The possibility that we could figure out how to tap these pre-conscious
processes for financial gain or for more wholesome purposes, such as improved
learning in school, makes this an intriguing area for study (albeit frustrating).
Below is one way that has been used to study this fascinating topic.
A tachistoscope, or t-scope, is an istrument that can flash
information before our eyes for very small and precise amounts of time.
There are two basic types: a flashtube tachistoscope and the shutter
tachistoscope. The flashtube t-scope uses a small lamp that is something
of a cross between the fluorescent tube in ceiling lights and the flash
tube used in a camera. The flash tube in a t-scope has very fast
"rise" and "fall" times in how fast it reaches maximum brightness and how
fast it turns off, and it can be kept "on" for very precise amounts of
time. This makes it possible to light up an image for a few milliseconds
at a time.
The image cards (red, green, and blue) are individually lit by the flashtubes
on the side. The red image shines through a half-silvered mirror
to reach the subject viewing through the left. The blue image shines
through a half-silvered mirror and reflects off of a second mirror to reach
the subject. The green image shines off of two mirrors. Timing
and sequencing is controlled with a computer. (Click for
A multi-channel flashtube t-scope uses mirrors in a large box so that
when subject looks in the viewng hole, any of several images that might
be lighted appear to be in the same place. In a typical experiment,
a "subliminal" image on a card is flashed for a few milliseconds, then
a "mask" card is flashed for a few milliseconds longer (with the subject
being unaware that the "subliminal" message ever appeared), and then some
other final target image is flashed for a second or two. The reason
for using the "mask" image is to flush the "subliminal" image from the
subject's retina. Ever notice that you see lights long after a camera
flash? Since the retina in your eye can thus serve as a form of memory,
and so we need to present another image to flush out the retina. (This
is why it is likely that you would recall seeing an "eat popcorn" frame
in a move if it had ever been done - as when you can clearly see the bubbles
at the end of a film reel.)
In an experiment using a three-channel t-scope as described above, the
subject would report seeing only the final target card, or perhaps noticing
some sort of flash preceeding the target card. In one experiment
(Tony Greenwald), subjects were presented with affect laden words
at the pre-conscious level of a few milliseconds. These would be
words that elicit some sort of emotional feelings, such as hate, love,
fear, disgust, etc. The final target word that was flashed at a conscious
level was a meaningless nonsense word (e.g., "prind"). A computer
was used to control the timing of presentations in the three-channel t-scope,
and was also used to collect information regarding the subject's response
to the final target word (and reaction time).
Interestingly, the researchers found that the pre-conscious affect-laden
word did appear to influence subject's feelings associated with the nonesense
target word, even though no subjects believed that they had seen anything
before the presentation of the target word. That is, a person's feelings
about a neutral object can indeed be influenced below the threshold of
awareness. However, the effects of such "subliminal" influence are
very short lived. Subjects who were asked to indicate the feelings
associated with the nonesense words a few minutes later provided resultes
that showed no correlation with the pairings that had been presented to
them on the t-scope.
A problem with the flashtube t-scope is that it is very cumbersome to
use. With its mirrors and flashtubes, it is large, heavy, and
fragile. For the poor subject, it is somewhat uncomfortable to sit
for some period of time with her/his head against the viewer of a large,
immobile box. Another instrument that can be used in a more natural
way and with larger groups of subjects is the shutter t-scope. Mechanical
shutters, much like what is used in a camera, are placed in front of slide
projectors. A computer is used to cycle the projector slides and
to open the shutters at the right times for the right amount of times.
Because the shutters are mechanical, they cannot be controlled with as
fine a resolution and with the same precision as with a flashtube t-scope,
but they are good enough for some applications. Using the two-channel
set-up shown below, it was possible to flash the iris-style shutters reliably
down to around 10 milliseconds at the center of the iris. (Click for
interface technical details. Click to
zoom image of shutters.)
T-Scope Shutter Set-up Screen (TOP)
T-Scope Shutters on Moving Cart (LEFT)
(click on image to zoom for details)
The shutter t-scope above was used in one study to see if it was possible
to influence a person's perceptions of a political candidate with pre-attentive
information (Jon Krosnick). An affect-laden word or object would
be flashed briefly before showing the photograph of a political candidate.
In another experiment, the sequencing shown on the screen above was used
to study the mere exposure effect (Tony Greenwald). The idea
of "mere exposure" is that people tend to form positive attitudes if they
are merely exposed to something - e.g., if a person sees an advertisement
several times that merely says, "vote for Smith," the person is likely
to form a positive attitude about Smith where we would expect no rational
reason to do so. With the settings of the screen above, subjects
were exposed briefly to such messages, followed by a mask (picture of a
quilt) for two seconds, allowing the experimenter to study the influence
of differences in exposure time on the mere exposure effect.
You might be wondering why we don't simply flash these things onto a
computer screen. There are three reasons why. First, the picture
on a CRT type of screen (cathode ray tube, or TV pucture tube) is painted
at a fixed rate of around 60 or 70 times per second (the vertical refresh
rate of the computer display card), a level of resolution that is inadequate
for the sorts of studies described above. Another reason is that
the picture on the screen (raster) is not simply flashed as is done
with the t-scopes described above, but is painted one line at a time, left
to right, top to bottom. (If you have a black and white TV set, you
can see these individual horizontal scan lines if you look closely.)
The top of an image can be displayed ten milliseconds before the bottom
of an image. Finally, the phosphors that make the light on the screen
(the cathode ray, or beam of electrons, hits the phosphor coating on the
screen, causing the phosphor to glow) do not "turn off" instantly, making
it impossible to precisely control the offset of the image. (Turn
off your computer screen in a dark room - notice that it will continue
to glow!) An LCD (liquid crystal display) screen suffers from similar
problems - the liquid crystal shutters are sluggish in onset and offset