Subliminal advertising and the psychology of processing unconscious stimuli: A review of research

Subliminal Advertising and the Psychology of Processing Unconscious Stimuli: A Review of Research Kathryn T. Theus Rutgers University

ABSTRACT

This article reviews progress to date on research on the effects of subliminal stimulation on subject populations and potential applications to persuasive communications. Three areas of inquiry covered in the literature include psychological, physiological, and behavioral (choice) responses, the last of which is of particular interest to advertising and marketing specialists. The article identifies several fruitful areas for continued research and experimentation, especially in areas of social marketing research. 0 1994 John Wiley & Sons, Inc.

Despite a nearly century-long quest to clarify the effects of subliminal stimulation, and more recently its potential effects in advertising and marketing, social scientists have been able to offer few hard conclusions concerning its effectiveness. Researchers have generally pursued three areas of inquiry in trying to determine what occurs when subjects are exposed to stimuli of which they are not consciously aware. These emphases include research on psychological, physiological, and behavioral (choice) responses, the last of which is of particular interest to advertising and marketing specialists. In this review of the literature, findings from each of the three emphases will be examined and applied to

Psychology & Marketing Vol. l l (3) : 271-290 (May/June 1994) 0 1994 John Wiley & Sons, Inc. CCC 0742-6046/94/030271-20

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advertising and marketing situations. Implications for alternative research directions will be discussed.

Laboratory psychologists first began exploring accuracy in perception in the mid-1800s by estimating thresholds whereby individuals could respond to stimuli without conscious perception of their existence. This line of investigation led to studies of involuntary motor-physical response through self-report.

In the late 1800s and early 19OOs, visceral and mental determinants of response became the focus in experimental psychology. Through dif- ferentiating between objective measures of motorphysical response and subjective report, researchers attempted to uncover psychological influences on perception. A distinction was made by psychoanalytic researchers between the inability to perceive stimuli and inattention to stimuli. Those interested in cognition and attitude development attempted to determine psychological blocks to conscious perception.

In a parallel vein during the 1930s, psychologists interested in motivation attempted to determine whether visceral or attitudinal response to subliminal stimulation influenced behavior. A long series of reinforcement studies indicated that behavioral response could be stimulated by imperceptible conditioning shock, or cues, to which subjects were not consciously attending (McConnell, Culter, & McNeil, 1958).

Work on subliminal effects since the late 1950s has investigated marketing and advertising applications of the question of effects on behavior, incorporating past research in motorphysical, cognitive, attitude, and conditioning research. Surprisingly, the earliest research in the area of advertising applications dates from 1913 (Hollingworth, 1913).

Definitions of subliminal have changed along with research foci. The subliminal threshold in early studies was defined as the stimulus intensity that is correctly perceived by the individual 50% of the time, or some other arbitrarily chosen figure (Weiner & Schiller, 1960). Lazarus and McCleary (1951) used the term subception to note the phenomenon that subjects can discriminate among stimuli even when they are unable to consciously identify stimuli. Erdelyi (1974), recognizing theories of selec- tive perception, which cause information processing to be independent of particular input, described perception as the conscious terminus of a se- quence of nonconscious processes.

Silverman’s (1976) definition reflects more nearly an advertising or marketing interest. He defined subliminal as “the absence of evidence that the individual is aware of the impinging stimulus before its effect is felt” (p. 311). By this definition, any stimulus can be subliminal if the observer is not attending to it consciously.

PSYCHOLOGICAL FACTORS

Psychological research has successfully shown the effect of symbolic, value, need, tension, tension release, emotions, and selectivity on the

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perceptual process (Bruner & Postman, 1947a, 194713, 1948, 1949; Bru- ner & Goodman, 1947; Carter & Schooler, 1949; Cowan & Beier, 1952, 1954; Lazarus, Ericksen, & Fonda, 1951). Research has also shown psychological need, conflict, and defense affect perception (McClelland & Atkinsn, 1948; McClelland & Liberman, 1949a, 1949b; Sanford, 1936). Psychologists concerned with unconscious perception sought to extend research on inner states to the perception of subliminal stimuli by employing two related research approaches: One dealing with the theory of perceptual defense, by which perception is associated with a multiprocess chain of events that begins with a stimulus input and terminates (subjectively) with conscious recognition, and the other with the theory of partial cues, a physiological and cognitive process invol- untarily determined by a particular stimulus pattern. Both offer ex- planations as to why subjects are able to respond to stimuli that are supposedly beyond the realm of conscious awareness.

Perceptual Defense Perceptual defense is the unconscious mechanism that resists the recognition of threatening stimuli (Blum, 1955). The pioneer experiment on this phenomenon was the McGinnies “dirty word” experiment. In this study, taboo words had elevated recognition thresholds and evoked GSR responses prior to the correct report of them by the subject (McGinnies, 1949). Dixon (1958) also found differences in perceptual thresholds for taboo words. Howes and Solomon (1950) argued that the difference in threshold between neutral and taboo words reflects a difference in familiarity and that in the case of taboo words, the subject may be suppressing rather than repressing a response. For research demonstrating similar findings, see Postman, 1953; Postman, Bronson, & Gropper, 1953.

Lazarus and McCleary (1951) simulated the anxiety response associated with taboo words by a pretest application of conditioning shock along with the presentation of nonsense syllables. The subsequent recognition thresholds for these taboo syllables were higher than for other neutral syllables, although there was no difference in familiarity among the syllables nor was there any reason to expect suppression (see also Howes & Solomon, 1950; McGinnies, 1949). McClelland and Liberman (1949a, 1949b) suggested that if anxiety is expected to raise thresholds, positive values should lower them. However, like experiments on defense, results from their sensitization studies were inconsistent. Some research indicated an increase in threshold for both positively and neg- atively toned words. Others reported a decrease for both (Banks, 1959; Bevan, 1964; Blum, 1955; Davis, 1959; Dulaney, 1960; Gilchrist, Lude- man, & Lysok, 1954; McClelland & Liberman, 1949; Reece, 1954; Spence, 1957).

In order to meet the methodological criticisms of the Lazarus and McCleary subception experiment, Dixon (1958) not only measured rec-

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ognition thresholds for emotional and neutral words, but also required subjects to guess the identity of subliminally presented words, to give free-association responses to these stimuli, and then to match their guesses to the stimuli they thought had been presented. Although no reliable increase in latency was noted for the emotional words, the emotional words provoked larger GSRs and several subjects matched their guesses to the stimuli that accompanied them more frequently than could be expected by chance. Questioning at several stages of the experiment revealed no evidence of awareness of the subliminally presented stimuli. Fuhrer and Erickson (1960) repeated Dixon’s experiment but were unable to obtain better than chance matches between presented works and guessed responses.

Several important review articles were generated out of this research tradition that are still useful in identifying the early directions taken in research on perceptual defense (Adams, 1957; Blum, 1955; Gilchrist et al., 1954; McConnell et al., 1958).

Along a similar vein, Bevan (1964) and others pointed to findings that demonstrate sensitization varies with individuals (Carpenter, Wei- ner, & Carpenter, 1956; Ericksen, 1952; Goldiamond, 1958). Kuilano (1954) found that hospitalized neurotics perceived emotional words at significantly lower thresholds than did a group of normal subjects. And Kretch and Calvin (1953) found visual discrimination of patterns at close to liminal values higher among more intelligent college students. Blum (1955) maintained that visual discrimination cues an avoidance reaction. Subjects were less likely to choose conflict-relevant stimuli than neutral from a group presented at subliminal speeds (Blum, 1955). Ericksen, Azuma, and Hicks (1959) reported that subjects can identify the affective quality of a stimulus word reliably when they fail at actual recognition. However, there was no evidence of a lower discrimination threshold for affective judgments than for specific identifications.

More recently, Zajonc (1980) has reviewed evidence from several studies showing that, under some circumstances, unattended stimuli can be processed through mere exposure, to a degree that is sufficient to elicit a subsequent affective reaction (i.e., like/dislike) without their being recognized as having been previously encountered (cognitively encoded).

Because of confusion and contradictions in findings of research related to perceptual defense, researchers began to point out that a rig- orous operational definition of perceptual defense was needed to anchor the concept in antecedent as well as in consequent conditions.

PHYSIOLOGICAL FACTORS

At the same time that theories of perceptual defense were being investigated, researchers were considering what effects could be attrib- uted to physiological thresholds, alone.

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Cues, Latency, and Response Research on physiological thresholds is rooted in a long-standing research tradition. As early as 1862, Suslowa (1863) applied low-intensity electrical currents to subjects to determine their ability to make two- point threshold discriminations even though these currents were below the limen of perception or threshold of awareness (Baker, 1937a, 193713). In 1883 Pierce and Jastions (1884) showed that subjects could discriminate between different weights significantly better than would be pre- dicted by chance alone, even though subjects had no confidence in their judgments. Others have also used the criterion of zero confidence to establish that discrimination below the limen of consciousness is possible. Color and shape discrimination at low levels of illumination and auditory and olfactory discrimination at low levels of stimulation have been demonstrated in laboratory experiments as measured by physiological response and verbal report (Baker, 1937a, 1937b; Byrne, 1959; Coyne, King, Zubin, & Landis, 1943; Fullerton & Cattell, 1982; Hol- lingworth, 1913; Laird, 1932; Miller, 1939; Sidis, 1898; Stroh, Shaw, & Washburn, 1908; Vinacrc, 1942; Williams, 1938).

However, unlike visual stimuli, not much evidence has been shown of effects from subliminal verbal stimuli. Auditory discrimination fails under two conditions: signal degradation (rapid speech) and channel capacity (word rates exceeding 300 per minute). Under such conditions, meaning is rendered unintelligible (Licklider & Miller, 1951). Subau- dible message thresholds may also be masked by other stimuli, and therefore rendered ineffective as subliminal phenomena (Broadbent, 1958; Dixon, 1971, 1981; Eriksen & Johnson, 1964; Kahneman, 1973; Petersen & Kroener, 1964).

Correspondingly, research has indicated that reliability of subject’s judgments increases with the intensity of the stimuli; that is, the accuracy of perception increases as stimulation approaches a supraliminal level (Lazarus & McCleary, 1951; Lowenfeld, 1961; Taylor, Rosenfeldt, & Shulz, 1961). Research has also shown that need states affect perception. However, individual differences affect the degree of response one might anticipate.

Sanford (1936) initiated work in this area as early as 1935 by showing that subjects who had been deprived of food were more prone to produce food relevant responses to stimuli. McClelland and Atkinson (1948) showed level of response to be systematically related to levels of hunger (McClelland & Liberman, 1949). Dixon (1958) attempted to find differences in physiological and the psychological thresholds by seeking differences between the perceptual threshold and a threshold for verbal report. Higher thresholds for the left eye were found to accompany taboo words, an early finding anticipating later brain hemisphere studies currently under way.

The literature indicates perception is a highly complex response or- ganized in a hierarchical fashion, some facets capable of appearance


prior to recognition or verbal identification. Boardman (1957) argued that subjects in subliminal perception experiments are capable of dis- criminating structural differences between words when tachistoscopically presented below verbal recognition levels, depending upon the presence or absence of electrical shock. With repeated trials, accuracy increased, e.g. learning took place. Goldberg and Fiss (1959) suggested this partial information hypothesis applies to the discrimination without awareness literature as well as to the subliminal perception data. They found partial cues facilitated performance; therefore, they inter- preted discrimination without awareness as an artifact. Bevan (1964) and others concurred (Bricker & Chapanes, 1953; Murdock, 1954; Voor, 1956). Hoisington and Spencer (1958) found that if the subject knows what to look for, he will have less difficulty in organizing his perceptual field. Weiner and Schiller (1960) found the number of correct identifications of ambiguous figures to be directly related to stimulus intensity of the identifying cue.

Thus, researchers suggested test attitude, familiarity with task, and partial cues as important considerations in the correct interpretation of perceptual defense and all other subliminal phenomena. Weiner and Schiller (1960) enlarged on the discussion by indicating that to assert true subliminality, researchers must be able to rule out the possibility of partial cues. They called into question findings of research on subliminality because of the imprecision of threshold definition. They suggested that those contending that no subliminal effect occurs must be able to demonstrate the presence of liminal cues, and that those suggesting that the effect does occur must be able to rule out the possibility of cuing (Giodian & Ericksen, 1959; Sharp, 1959; Spence & Bressler, 1962).

PSYCHOLOGICAL AND PHYSIOLOGICAL EFFECTS ON ADAPTIVE BEHAVIOR

In the past 15 years studies have built on the themes of perceptual defense and partial cues as applied to areas of adaptive behavior and cognition. Research on the relationship between subliminal stimulation, attitude, and behavior purports to demonstrate Freudian psychoanalytic theory by using subliminal messages to influence the behavior of neurotically and psychotically depressed individuals. Freudian theory ascribes depression to the process of turning unconscious aggressive wishes against oneself.

In a series of 16 experiments, Silverman (1976) tachistoscopically presented “Destroy Mother” to an experimental group of depressives and “Thinking People” to a depressive control group. The experiment yielded higher self-ratings of depression for the experimental groups only. In further tests with schizophrenics, depressives, homosexuals,

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and stutterers, Silverman found positive results only when stimuli were specific to their conditions. Further work supporting the effectiveness of subliminal primes has shown facilitation of recognition time for words (Spence, 1983); improvement of agoraphobic tendencies among patients (Lee, Tyrer, & Horn, 1983) and the positive adaptation of schizophrenics when “oneness fantasies” with others of importance are subliminally suggested (Silverman, Lachman, & Melich, 1984).

Among the interesting studies along this latter theme, Schurtman, Palmatier, & Martin (1982) showed that subliminal exposure of alcoholics to the message “mommy and I are one” (experimental) and “people are walking” (control) lowered anxiety and depression, en- hanced self-concept, and reduced alcohol consumption after a three- month follow-up. Other studies of a similar nature suggested that psychodynamic effects can stimulate academic performance, reduce pathological thinking, and reduce heroin use among addicts, provided care is taken both to select relevant psychodynamic content and to select candidates for whom there is reason to believe this content is particularly relevant (Bryant-Tuckett & Silverman, 1984; Dauber, 1984; Jackson, 1983; Parker, 1982).

The work of Silverman and Schurtman and their use of Subliminal Psychodynamic Activation (SPA) has stimulated considerable debate over the validity and rigor of the method (Balay & Shevrin, 1989; Fi- gueroa, 1989; Fudin, 1987; Silverman, 1989; Weinberger, 1989; Wer- man, 1984). In a quantitative review of SPA, where the results of meta-analyses were corrected for statistical artifacts, small but significant effects were, nevertheless, revealed (Hardaway, 1990). Similarly, in an extension of the original work, Gustafson and Kallmen (1990) used cognitive (Gestalt) and motor (following a printed line with non- dominant hand) tests and found a significant improvement in motor performance scores after the delivery of a symbiotic message as com- pared with a neutral one. And Talbot, Duberstein, and Scott (1991), in a study of the effects of a message related to loss and separation (mommy is leaving me) versus a neutral control (Mona is loaning it) found that subjects exposed to the experimental message reported less confidence in their interpersonal attractiveness than did those subliminally shown the neutral stimulus, supporting the hypothesis that semantic analyses are performed unconsciously. In addition, those subjects exposed to the subliminal message ate significantly fewer crackers than those exposed to the neutral message. Interestingly, when subjects were exposed to a supraliminal message, those confronted with the loss message tended to eat more crackers than the control. This finding suggests that the subliminal message may bypass ego defenses, and supraliminal messages stimulate action-oriented defense against anxiety.

A focus on the production of anxiety states through subliminal messages has produced a related strain of work. Erdley & D’Agostino (1988) suggested that subjects subliminally exposed to honest-related words


projected over an ambiguous face, resulted in higher ratings of honesty; he achieved similar findings for mean-related words. Similarly, state anxiety was raised in an experimental group subliminally exposed to threatening images (Robles, Smith, Carver, & Wellens, 1987) including such feelings of isolation, reaction formation, and introaggression (Wes- terlundh & Terjestam, 1987). Mendelsohn and Silverman (1982) suggested, however, that once a stimulus that activates disturbing mental content reaches awareness, its status as a motivator may be diminished.

Neidenthal(1990), in experimental pairing of slides of novel cartoon characters with undetectable slides of faces expressing joy or disgust, found faster recognition by subjects when pairs were consistent, and higher ratings of disgust or joy when those conditions were paired ap- propriately. This outcome provides some evidence for the role of non- verbal, implicit cues in reinforcing or strengthening social perception.

Other studies have focused on the differential perceptual capacities of the brain, looking particularly at brain hemisphere. Barkoczi, Sera, and Komlosi (1983) found the right hemisphere to be superior in the preprocessing of emotionally loaded stimuli. Carlson (1989) found signs of repressive plus isolating defenses associated with the left hemisphere and more projection plus regression with the right hemisphere, indicating differing perceptual styles or ego defense mechanisms. Yahnke (1989) found that left hemisphere cognition was more sensitive to subliminal stimulation than bilateral processing.

Research has also shown that a subject's attitudes toward unfamiliar subliminally presented stimuli become significantly more positive with repeated exposures. Bornstern, Leone, & Galley (1987) suggested that, based on Freud's theory of individual preference for the familiar, individuals will build positive affects toward objects as they become more familiar with them, particularly if the individual does not have a mental representation of similar objects with which to compare (e.g., past experiences can have no influence on affective judgments of new, unfamiliar objects).

POTENTIAL EFFECTS OF SUBLIMINAL STIMULATION

What might be expected in response to subliminal messages is murky and contradictory. What may be true in laboratory experiments may not be true for nonlaboratory conditions. A summary of research thus far has established the following possible effects:

The closer to the threshold of awareness, the more effect stimuli are likely to have. However, establishing a consistent threshold is a problem, as individual thresholds vary from day to day. People can make use of subthreshold cues in making difficult perceptual judgments. Visual effects are more probable than auditory effects.

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People can learn (be conditioned) through subliminally presented stimuli. Psychodynamic effects may also be demonstrated under these conditions, provided subliminal messages conveyed are relevant to the subjects chosen. For subliminal perception to be effective, it must be incorporated into some drive system. Subjects may not respond to stimuli of which they may be aware that are completely liminal. Repetition of subliminal stimuli may increase the chance of behavior but it may also raise the stimulus above the limen of awareness. Unilateral brain processing may contribute to differential ego defense mechanisms, and may be more affected by subliminal stimuli than bilateral processing.

CHOICE BEHAVIOR: A SPECIAL CASE FOR ADVERTISING AND MARKETING

The question of particular interest in the fields of advertising and marketing research is whether or not subliminal suggestion can be choice specific. Can weak or unobtrusive stimuli prompt choice behavior such as buying refreshments at movies or selecting certain kinds of mer- chandise? The issue has been of concern since the autumn of 1957 when Vicary claimed to increase concession sales in a movie theater through the tachistoscopic presentation of the phrases “Eat Popcorn” and “Drink Coca Cola” at 1/2000 of a second (Bevan, 1964). Even so, there have been relatively few controlled studies of the effectiveness of subliminal stimuli on preference or choice, and the results have often been contradictory.

Champion and Turner (1959) showed a film that included the subliminally presented slide of a bowl of rice labeled “Wonder Rice.” Af- terward, experimental groups performed no better than the control when asked to identify the bowl of rice by the brand name. Calvin and Dollenmayer (19591, in a guessing game format flashed subliminal instructions “choose left,” “choose right,” to subjects, but the instructions failed to influence choice behavior so long as they were subliminal. Similar negative results were also obtained by Vernon and Badger (1959).

Likewise, Byrne (1959) flashed the word “beef” for 1/200 of a second to subjects watching a film. Following the film subjects rated themselves for hunger and then were encouraged to pick a sandwich from a variety presented to them. Those in the experimental group were hungrier than those in the control, but were not more apt to choose beef sandwiches.

Hawkins (1970) replicated the Byrne study by presenting the word “Coke” at below subliminal threshold levels to an experimental group.


The message was able to produce greater thirst ratings among the experimental group than a nonsense syllable did in the control. Other researchers have not been able to produce this finding (Beatty & Haw- kins, 1989; Saegert, 1979). For example, researchers attempting to correct methodological weaknesses of previous experiments, in two studies presented at subthreshold levels, “Hershey’s Chocolate,” to an experimental group and no message to a control watching a film. No support was found for claims of choice behavior (George & Jennings, 1975).

Testing for attitude change in marketing situations has not yielded much support for the influence of subliminal stimulation either (George & Jennings, 1975). Kolees (1957) in an experimental study of cognitive functions, found subjects identified the subliminal figure correctly more frequently than controls, and solved more problems correctly than did controls. However, Gerard (1960), in replicating the study, was unable to obtain positive results. Zuckerman (1960) elicited increased writing with an experimental group when instructions to do so were tachistoscopically superimposed on pictures they were asked to describe, and elicited less writing when instructions were “don’t write.” Dixon (1971) and Moore (1982) suggested these results were due to a methodological artifact called “ceiling effect” when performance reaches an asymptote and cannot be improved upon. The dropping off may have been due to fatigue. In any case, the finding has not been replicated.

Wilson Bryan Key contended that advertising embeds in messages, not consciously attended to, are perceived and stimulate an emotional response as well as identification with the brand name. Further, he suggested advertisers commonly use embeds as an effective selling de- vice. In a poorly designed and reported study, Key tested over 1000 adults, both male and female, who were shown a gin advertisement that contained sexual embeds. Subjects were asked to describe their feelings as they looked at the ad. Key reported that 62 percent of the subjects claimed feelings of sexual stimulation or excitement (Key, 1972, 1976, 1980).

Kelly and Kessler (1978) (Kelly, 1977), attempting to test whether ads with subliminal embeds stimulate greater brand name and ad recall than similar ads without embeds, found no difference between a control and test group immediately after treatment. Nor did the researchers find a “sleeper effect” operant a full week later. Similar studies have also found negative effects (see also Caccavale, Wanty, & Edell, 1981; Dixon, 1971; Mobley & Boles, 1980; Zajonc, 1980).

Bagley and Dunlap (1980), in setting out to correct Key’s methodology, found a significantly higher percentage of response to two ads with sexual embeds of four used. The Bagley and Dunlap study was criticized as only an improvement over Key’s study, failing in the important task of measuring the degree of effect ads had on subjects and of effect on brand attitude, purchase intentions, or brand recall. Kil-

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bourne, Painton, & Ridley (1985) in studying the effectiveness of sexual embedding in advertising, found that galvanic skin response measurements were heightened for versions of the ads with embeds, which may influence viewer’s evaluations of ads. Other research (Gable, Wilkens, Harris, & Fernberg, 1987; Rosen and Singh, 1992) in experiments with embedded variables, found that subliminally embedded, sexually oriented stimuli do not influence consumer preference.

DeFleur and Petranoff (19591, in an experiment with closed-circuit TV and commercial TV, found communication using subliminal messages over these media to be possible, but messages are ineffective as persuasive devices. Vokey and Read (1985) likewise examined the impact of subliminal messages in popular music and in advertising and found no evidence to support a claim of impact. They did find evidence to suggest that the apparent presence of backward messages in popular music is a function more of active construction on the part of the per- ceiver than of the existence of the messages themselves. And in double- blind tests of subliminal self-help audiotapes, three replications showed that products did not improve memory or increase self-esteem as claimed; however, general improvement for all subjects occurred in both memory and self-esteem, and more than a third of the subjects had the illusion of improvement specific to the domain named on the tape’s label (Greenwald, Spangenberg, Pratkanis, & Eskenazi, 1991).

Kotze and Moller (1991) attempted to relate choice behavior to personality correlates, suggesting that low anxiety, less neurotic, and more extroverted individuals would be more susceptible to subliminal messages. The experiment exposed subjects to subliminal messages urging subjects to choose symbols instead of numbers or letters. Although no support was found for the hypothesis, the researchers suggested that the outcome may have occurred because the messages were neutral and subjectively meaningless, and did not relate to the subject’s needs or motivation. With such a psychodynamically irrelevant message, it may be likely that subliminal stimulation will be less effective and that stable personality dispositions such as extraversion will exert less influence on susceptibility.

Krugman (1977), writing in support of subliminal effects, suggested that advertising research should pay attention to the different functions of the hemispheres of the brain. Asserting that the right brain absorbs images while the left brain controls verbal recall, he projected that in scanning ads, the eyes (and mind) must take in stimuli through pe- ripheral vision while rejecting a great deal. This process of selection establishes what material to attend to. He suggests that the “picture taking” ability of the right brain screens the environment to select the material the left brain should focus on. Cuperfain and Clark (1985) tested a model of subliminal stimulation based on studies of information processing by the right hemisphere and found significant effects on

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stated preference for highly advertised products when subjects viewed tachistoscopic presentations in the context of a film concerning woolen- clothing soaps, but not for relatively unknown ones.

Saegert (1979) suggested the reason subliminal influence has not been found in choice behavior studies is that studies have not concen- trated on isolating subjects who can be identified as harboring specific unconscious wishes. Zajonc (1980) reviewed a number of studies that indicate affective reactions to stimuli can occur even in the absence of recognition memory. He asserted one can like something or be afraid of it without actually knowing what it is and proposed that the affect may be processed through a related but different system from that used to assign meaning and process information.

In response to Moore’s (1982) suggestion that choice behavior is prob- ably not affected by subliminal stimuli, Cuperfain and Clarke (1985) warned advertisers not to discount its use too quickly. They suggest that consumer attitudes may be positively affected by advertising for image creation, preference, or some other objective short of actual purchase.

SUMMARY

Research on brand choice behavior, per se, seems to be subject to little or no influence by subliminal suggestion. But in looking at research on subliminal perception generally, certain themes might be effectively applied by advertising or marketing specialists hoping to use subliminal techniques to make a difference in consumer attitude and/or perhaps consumer preference. Limited evidence suggests that need-state behaviors may be stimulated, as well.

First, research suggests that the kind of subliminal stimulation makes a difference in effect. Subliminal visual stimuli appear to have a much higher probability of being cognitively processed by subjects than do auditory stimuli. In studies of perceptual defense, semantic material used to arouse need states resulted in significant precognitive effects. Thus both the message used and the approach to messages should be considered in applying findings from studies of perceptual defense. Media such as print, film, video, and other visual stimuli might be considered for campaigns, using carefully considered familiar images and words for arousal.

As important as the kind of stimulation, is the kind of target audience stimulated. More segmentation based not on traditional demographic variables, but on psychogenic or need-based states, should enhance the effectiveness of subliminal advertising or communication campaigns. Psychodynamically irrelevant messages will be less effective for stable personality dispositions, studies indicate. If there were a way of ensur- ing that the messages conveyed were relevant to the subjects chosen with respect to their own psychological drives, then potential effects

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might be predictable. It seems important that studies of susceptibility match the content of the subliminal message to the psychodynamics of subjects. Then one may assess whether susceptibility to subliminal stimulation is related to personality variables, as tentative reports in the literature have suggested (Dixon, 1981).

Given these two a priori conditions, some research shows that as long as subliminal cues remain subliminal (do not exceed the threshold of conscious recognition) stimuli may be processed more readily than liminal stimuli to which subjects are inattentive. But at the same time, the cue should be as near the liminal threshold as possible. Research suggests that such subliminal messages may bypass ego defense mechanisms, stimulating behaviors that defenses to liminal messages in- hibit. Thus, in recent experiments with messages pertaining to loss which produced depressed food consumption as well as feelings of lowered self-esteem, actual behaviors related to messages were observed. Behavioral indices may be more sensitive indicators of Silverman’s SPA influences than either self-report measures or projective measures (Bornstein, 1990; Talbot, Duberstein, & Scott, 1991). Further, just as Silverman and Weinberger (1985) have written about the subliminal message, “mommy and I are one,” as a ubiquitous therapeutic agent, Talbot et al. (1991) suggests that “mommy is leaving me” may have a ubiquitous antitherapeutic effect.

Repetition of cues or images may also predispose subjects (or consumers) to view a brand advertisement more favorably, although previous positive experiences with a specific or favorite product may override potential receptivity to a new product with which a consumer has had no experience. (In this case, direct distribution of free product samples prior to launching a subliminal campaign might enhance its effectiveness, just as in a traditional campaign.) In any case, prolonged campaigns will more likely have impact.

Along a similar vein, repetition of subliminal cues may also heighten the arousal of need states, as shown in perceptual defense studies. Under conditions of moderate arousal, positive affective states may be generated. Under conditions of high arousal, however, the consumer’s in- herent response to the product, whether more or less favorable, may be induced (Singh & Hitchon, 1989). If effects of subliminal cues correspond with studies of arousal generally, intense arousal may provide a favorable climate for immediate response, e.g., purchase through an 800 number, consumption of a product already purchased or available readily, or delayed purchase behavior (Singh & Hitchon, 1989).

Research on brain hemispheres and information processing compli- cates the notion of successful marketing or advertising applications further. The variability in findings of experimental studies of choice behavior may be affected by this uncontrolled and subtle intervening variable. Even if left-handed (right-brained) individuals process emotionally laden material more effectively than others and right-handed


(left-brained) individuals are more sensitive to subliminal stimulation than others, we have too little information about the prevalence of bilateral processing, which i s not particularly vulnerable to subliminal suggestion and may comprise a large number of potential consumers to estimate effects. Subliminal messages do appear to reinforce stated preference for highly advertised products among right-brained individuals. The difficulty for advertising and marketing applications, ob- viously, is that traditional target populations cannot be easily seg- mented by brain function.

Nevertheless, perceptual defense research suggests that subliminal advertising may provide new opportunities for modifying social behavior through public or community awareness campaigns, which do not require publics to select specific brands from among product types, but call for more generalized responses to suggestions that enhance personal performance, improve or consolidate attitudes, or facilitate adjustment. If experimental manipulations targeting heroin or alcohol users can induce more positive self-images and less reliance on those drugs over prolonged periods in experimental situations, there is a t least a potential for such effects in nonexperimental conditions. Applications could be made to the drug problem in the United States, to seat-belt use, to smoking, to physical abuse, to sexual harassment, or to any number of public issues that affect large portions of the population.

To the extent that product advertising may also support such social outcomes, then the building of a context, image or favorable climate for a product within that social milieu may have some associative ben- efit.

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Subliminal advertising and the psychology of processing unconscious stimuli: A review of research