This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.

Contribute Thoughts | Search Serendip for Other Papers | Serendip Home Page

Biology 202
2000 Second Web Report
On Serendip

What You Don't Know You Know


Mridula Shrestha

FACT: In 1957, James Vicary, a market researcher, claimed that over a six-week period, 45,699 patrons at a movie theater in Fort Lee, New Jersey were shown two advertising messages, "Eat Popcorn" and "Drink Coca-Cola" while they watched the film Picnic. Once every five seconds, one such message, 3 milliseconds in duration, was flashed throughout the movie: a duration so short that the viewers were unaware that they were being flashed at all. Despite this unawareness, Vicary claimed that over the six-week period the sales of popcorn rose 57.7% and the sales of Coca-Cola rose 18.1% (1).

UNCERTAIN: Whether Vicary's results are reproducible, and whether subliminal messages significantly affects a consumer's decision to buy a product. In an interview with Advertising Age in 1962, Vicary confessed that his original claims were a "fabrication" (1).

Subliminal perception has been a controversial topic ever since it came into discussion, and till today, neither scientists, nor marketing professionals, nor laymen, have been able to come to definitive conclusions as to whether or not it is a "valid" phenomenon. It is a fascinating, and rather frightening, thought, that things we are unaware of perceiving may significantly affect our choices and decisions. In this paper, let us take a brief look at the phenomenon and try to place it in the parameters of what we know (or think we know) about neurobiology.

When you really think about it, it is not all that bizarre that we may be unaware of perceiving things that do in fact influence our behavior. When is the last time you were conscious of perceiving the wavelengths of light that allow you to think of something as blue? When did you last think, "oh, this particular sound wave I am perceiving right now contributes to helping me hear this note?" Yet it is with the integration of these very light and sound waves that we can see and hear. Perhaps awareness is overrated after all.

There are a million things that our bodies constantly receive as input that we do not constantly think about: outside air pressure, the force of gravity, heat, etc. Internal conditions, too, like blood sugar levels, pH, and breathing and heart rate are not normal topics in our "conscious" thought. But we know we perceive these and many other conditions: in the absence of homeostasis or normalcy (i.e. conditions within the range we are used to), we do detect the difference in some way.

So why should we be so surprised to hear that what we don't know affects us, does? Given that it does take time to think-that our "consciousness", or I-function, probably operates with physical processes that occur at non-instantaneous rates, we cannot expect that every single bit of input we receive, or generate internally, for that matter, go through the I-function. At any given instant the available inputs are colossal: there is radiation from the environment, the chatter of birds and the rustling of trees, the changing spatial ratios between us and a given stationary point as we walk, the chemical makeup of our bodily fluids, the humidity of the air, and yes, the semi-funny story our roommate is telling us with great enthusiasm. And so on and so forth. We cannot be conscious of everything that is happening: it's called limited attentional resource. We must budget it, much as we budget household incomes and 24-hour days. Scarcity makes us choose. And so we don't think about the song lyrics when our friend is crying on our shoulder. We don't notice how many different shades of blue there are in the sky when we're admiring the pink and purples hues of the sunset. This is our extremely limited subset of reality-our consciousness, our awareness, allows us to allocate our attention to only so much. But that is not to say that our bodies do not perceive much more.

Let's leave the abstractions aside for a moment and talk about experiments. Subliminal messages can occur in a variety of ways: the key is to keep the perceiver's I-function unaware of the subliminal inputs. This of course involves some clever hiding. But the way you hide the subliminal message, as an advertiser or a scientist, is pretty open: common methods are flashing images on screens with a tachioscope under the threshold level for perception (as was supposedly done in Vicary's study), playing auditory messages during sleep, hiding images in larger images, and writing or playing messages backwards (2). It seems it is not all that difficult to slip in something and simultaneously have it escape one's "attention".

In perhaps the earliest studies of subliminal perception (around the late 1800s and early 1900s), people were presented with visual stimuli at a great distance, so all they could "see" were dots, or with auditory stimuli whispered so faintly that they could not "hear" them. Following the presentation of the stimuli, the subjects were asked to make guesses regarding the stimuli-for example, if the stimuli were either digits or letters, they would have to identify which of the two the stimulus just presented had been-and it was found consistently that their guesses were more accurate than could be expected on the basis of chance alone (1).

In the 1970s, British psychologist Anthony Marcel performed subliminal priming experiments, based on previous findings that seemed to show that decisions about a stimulus are facilitated when the stimulus follows a related stimulus. In one of Marcel's studies, subjects were asked to identify a letter string as a word or a nonword; it was found that subjects could classify a letter string as a word faster if it was preceded by a "semantically related word." Marcel found that related words primed subsequent word/nonword decisions even when the priming words were "presented under conditions that made it difficult if not impossible for the observers to distinguish when the words were present from when the words were absent." (1)

Patients with some neurological damage also seem to exhibit some instances of subliminal perception. For example, people with blindsight, who have damage to the primary visual cortex, are often "unaware of perceiving stimuli within a restricted area of their visual field." (1) Blindsight patients may have normal vision for stimuli presented in all but a certain area of the visual cortex-in this area, they are unaware of stimuli being presented. But while the patients claim not to see stimuli located within that area, they are often "able to guess the size, shape or orientation of the stimuli they claim not to see." (1)

Propagnosia is a condition where people are unable to recognize familiar faces. Yet, given two familiar faces and two names, some patients with propagnosia can identify which name goes with which familiar face (faces that they claim not to recognize at all). Here again we can see that we might know more than we think we know, and that processes that bypass the I-function may help us process or put to use information that we do not "know" to exist.

One of the most compelling studies regarding subliminal perception involves surgical patients under general anesthesia. Most patients claim not to remember any events that occurred during anesthesia (fortunately), but "when memory is assessed by more indirect methods, there appears to be some memory for events during anesthesia...if the words guide and proud had been presented during anesthesia, then the patients may be more likely to complete the stems gui_ _ and pro_ _ with letters that produce guide and proud than with letters than produce other possible words." (1) This study is the hardest for me to digest, mostly because in the others, the subliminal perception occurs, or seems to occur, rather, in conjunction with conscious perception. Here, subliminal perception appears to be feasible in the absence of consciousness altogether. But this brings us back to the question of how important consciousness is, after all, in regards to perception. If indeed all perception does not have to be processed by the I-function, then it is logical and expected that it should occur not only in parallel to it, but also its absence, independently.

It is not surprising that the advertising industry would be very interested in applications of such research: after all, the ability to influence a person's choices and decisions, whether subtly or blatantly, certainly empowers the industry. As Michael Buchennroth writes, "Since the 1930s, advertising researchers and the corporations they represent continually pioneer understanding of the human mind. In the past they measured things like galvanic skin response, pupil dilation with the pupilometer, heart rate, body temperature, and so on...Now they measure things such as waves indicative of eidetic images, images before thought, images before dreaming, P300 or N100 waves, event-related potentials, and evoked potentials (EP)." (3)

EPs are a "computer generated wave obtained by repeatedly administering a stimulus such as a flash of light to subjects some 200 times. An EEG measures the resulting electrical brain wave activity. A computer, by averaging results, abstracts the response evoked by that specific flash of light stimulus form the sea of background waves of the brain's normal electrical activity...This process can obtain EPs from any specific part of the brain." (3) Thus, according to Dr. Howard Beck, "EPs are like a fingerprint of the brain." (3)

Further, "the wave measured 20-30 milliseconds after a stimulus originates in the brainstem." Importantly, "it registers even in unconscious subjects." 100 ms after the stimulus, the N100 wave appears, originating from the cerebral cortex, "where sensory input is processed and synthesized, and depending upon the stimulus, in differing brain hemispheres. The P300 wave appears with a sudden or unpredictable stimulus [such as a subliminal flash of light]. The P300 wave measures decision making ability." (3)

So, by studying EPs, researchers have "mapped varying brain functions. They have mapped what part of the brain thinks before we're consciously aware of thinking. They have identified specific electrical activity that occurs prior to thought, prior to imaging, prior to dreaming, prior to comprehension...prior to consciousness or activity that occurs without test subjects' knowledge that either the brain wave electrical activity or the stimulus ever existed...Researchers are no longer concerned with consciousness or awareness...that might be one difference between mind and brain. One is simply similar to a pail of saltwater, as Dr. Hal C. Becker recently said in a 'Newsweek' article, with abundant potassium and sodium and all the accompanying electrical activity similar to a potato battery. The other I suppose is Mr. Potato, only a little more self-aware." (3) This is an analogy to the nervous system model we have developed in class, a battery of saltwater with an I-function that allows for some personality. If everything Dr. Buchennroth writes in his thesis is true, then we can be sure that events we are not aware of can physically change nervous system activity. Thus, we have here another piece evidence for perceptual work done without the I-function.

It should not shock us then, when Wilson Bryan Key writes books like 'Subliminal Seduction' and 'Media Sexploitation', which bring to our attention the idea that advertisers use subliminal sexual symbols or objects to entice consumers to buy and use products. Key "says that thousands of ads in major magazines have the word 'sex' and four-letter words secretly embedded in ice cubes, shadows, and backgrounds. A Hilton Hotel room-service menu has 'sex' embedded from breakfast through dinner, 'sex's' saturate the cover of Eldridge Cleaver's 'Soul on Ice' and even the Sears Catalog is loaded with 'fascinating subliminal perversities." (4) In other words, sex sells, and advertisers know it.

So now we should all be extremely terrified that "our body has a mind of its own," that anyone can sneakily make us believe, buy, vote for, anything they like. Right? Wrong. In light of all our evidence, all we can say is that yes, we are probably capable of receiving input without intervention from the I-function. But we have no strong evidence to show that something like the decision to believe something, buy something, or vote for someone, happens in the absence of the I-function. Ultimately, our choices, our decisions, may not be swept so easily by random subliminal inputs-so the 'sex' written on the ice cubes in the Gilbey's gin ad (4) may conceivably register in our brains-but this is not to say that we will all go out and buy cases of Gilbeys. Do we all go out and buy everything that is advertised? Why do some ads appeal to some people and not others? Clearly there is more to advertising resulting in successful selling of a product than just presentation-and I-functions probably have a lot to do with that. If Gilbey's were to write 'sex' blatantly on its ads, would its sales necessarily go up? I doubt it (but perhaps I am na´ve about human nature :)). It is one thing to perceive something, and another to act upon that perception in a particular fashion.

The only studies discussed in this paper that imply otherwise are Vicary's (which, was, by self-admission, was a hoax) and other marketing research that has claimed that sales have gone up with subliminal advertising techniques (most of these have been called questionable. The others, like subliminal perception by the anesthetized, the blindsighted, the propagnosiac, the primed subjects, and even the mapping with EPs, point only towards the existence of subliminal perception, and not its ability to influence decisions beyond recognition of what the subliminal stimuli were. As I found from most sources, the evidence of actual effects of subliminal perception on behavior are "empirically recalcitrant" (5) and "subtle" (2). In fact, as Dr. Merikle writes, "Findings from controlled studies indicate that subliminal perception, when it occurs, reflects a person's usual interpretations of stimuli." (1) The findings do not, however prove that people, based on these subliminal perceptions, can be manipulated to make judgements or choices that reflect something more than simply the perception of the stimuli. The decision to take that perception and transform it into a purchase or a vote, with the given evidence, cannot be attributed to subliminal perception, and need not be considered independent of the I-function. So as much as I was tempted to slip in the number 10 and the letter A throughout the paper, it looks like it wouldn't help me very much (shucks).

_______________________________________________________________________ Note: This may be a ridiculous thought, but I'll propose it anyway: the good thing that may come out of knowing that subliminal perception probably exists, is a way to localize the I-function. If indeed we can map brain activity in every part of the brain with EPs (as discussed earlier in the paper), and subliminal perception is the perception of stimuli without involvement of the I-function, then all other things held constant, the difference in brain activity represented in conscious perception and subliminal perception should represent the workings of the I-function. The localization of that difference, then, would be a step towards the localization of the I-function. But of course this is probably an silly as well as infeasible idea: first, of all, if the brain tends to do things in several different ways, then we should not assume the I-function can be localized to one particular place, and secondly, however would we hold all other things constant when studying something as dynamic as the brain?

Related Topics: Posthypnotic suggestions, perceptual threshold or latency, priming, Response Window Procedure, Jung's personal and collective unconscious

WWW Sources

1) Subliminal Perception, an article from the Encyclopedia of Psychology

2)Sublim, a concise introduction to the study of subliminal perception

3)Subliminal Advertising Effects In Magazine Advertisements-by Michael L. Buchenroth, the introduction to a thesis about Subliminal Magazine Advertising by a graduate student at Ohio State University

3)Subliminal Advertising Effects In Magazine Advertisements-by Michael L. Buchenroth, the introduction to a thesis about Subliminal Magazine Advertising by a graduate student at Ohio State University

4)Subliminal Advertising Effects In Magazine Advertisements-by Michael L. Buchenroth, the third chapter of a thesis about Subliminal Magazine Advertising by a graduate student at Ohio State University

5) Replicable Unconscious Semantic Priming , an article published in the Journal of Experimental Psychology

| Course Home Page | Back to Brain and Behavior | Back to Serendip |

Send us your comments at Serendip
© by Serendip '96 - Last Modified: Wednesday, 02-May-2018 10:52:54 CDT