PerceptualandMotor Skills, 1991, 72, 315-322. O Perceptual and Motor Skills 1991
SUBLIMINAL STIMULATION, CHOICE BEHAVIOR AND SOME PERSONALITY CORRELATES O F SUBLIMINAL SENSITIVITY ' HENDRIK F. KOTZE Unit for Clinical Psychology University of Stellenbo~cb
AND
ANDRE T. MOLLER UniuersiQ of Stellenbosch
Summary.-The aim of this study was to investigate the possible relations between specific personality variables and the effect of subliminal stimulation on choice behavior. It was hypothesized that subjects with low anxiety, less neuroticism, and external locus of control and the trait of extraversion would be more susceptible to subliminal stimulation, 38 undergraduate students were exposed to subliminal messages urging them to choose symbols instead of numbers or letters. Analysis showed that subliminal stimulation did not generate a preference for symbols over numbers or letters. No support was observed for the hypothesis of an association between susceptibility and personality variables. These results may be explained in terms of symbol choice being a neutral message that did not relate to the subjects' needs and motivation.
A review of the literature on subliminal perception by Dixon (1981) has demonstrated that the phenomenon as such does indeed exist; however, as far as choice behavior is concerned, Dixon (1971) concluded that ". . . the evidence suggests that, whereas verbal behaviour can be affected by subliminal stimuli, these may have little effect upon other overt acts of choice" (p. 176). Dixon based his conclusion on studies by Byrne (1959), Goldstein and Barthol (1960), and Goldstein and Davis (1961) which suggested that, while "stimulus registration without awareness serves to modify or increase subjects' level of motivation or arousal . . . the overt behaviour which occurs in response to the increased motivation will be more closely related to subjects' past history of reducing this motivation" (Goldstein & Davis, 1961, p. 254). The question arises as to whether the effect of subliminal stimulation on choice behavior might be related to personality variables. Since Eagle (1962) suggested that some subjects are more sensitive to the effects of subliminal stimuli than others, various studies investigated the susceptibility to subliminal stimulation. A review of the factors related to the appearance and strength of sublirninal effects suggests that individual differences in hemisphericity are associated with the strength of subliminal perception. Several researchers showed that a relaxed rather than a focally alert state of mind increases sensitivity to subliminal stimulation (Bloem, 1973; Dixon, Hentschel, & Smith, 1984; Eagle, 1962; Murch, 1969). Eagle (1962) noted 'Requests for reprints should be addressed to Hendrik F. Kotzi, Unit for Clinical Psychology, University of Stellenbosch, Stellenbosch 7600, South Africa.
that subjects high and low in sensitivity showed different cognitive styles, which he described in terms of the following dimensions: (1) receptivity to inner cues, (2) ability to relax cognitive controls, and (3) style of attention deployment. Similarly, a study of Alison (1963) showed that, when subjects were encouraged to think intuitively, globally and freely, subliminal effects were demonstrated. No effects were found when they were encouraged to thlnk in organized, analytic, and logical modes. Murch (1969) also found that subjects who used intuitive strategies showed greater subliminal effects than those subjects who used an analytical approach. Similar results were reported by Hansen (1984) and Sherrod (1972). Sackeim, Packer, and Gur (1977) suggested that the terms used to describe the characteristics of individuals who appear to differ in susceptibility to subliminal perception, are similar to those used to characterize individuals who differ in hemisphericity. Their study indicated that the effect of subliminal cues upon perception of a neutral face is significantly more pronounced in subjects showing the general trait of right hemisphericity, as indicated by direction of eye movement upon interrogation (Day, 1967). They also found that a relaxed state favoured subliminal perception of the neutral face but again this was only true of the subjects with right hemisphericity. These results, indicating that hemisphericity and cognitive set interact in producing subliminal effects, led Dixon (1981, p. 34) to conclude: "Evidently low arousal, as well as right hemisphericity, makes for susceptibfity to stimuli below the awareness threshold." Other variables associated with susceptibility to subliminal stimulation have also been described in the literature. Shevrin (1984), for example, stressed the relationship between the type of stimulus presented and the motivational state of the observer. The same stimulus might evoke a wide range of reactions from different individuals; the process of perception is highly idiosyncratic and is coloured by factors like the individual's needs, values, emotional state, defence mechanisms and cognitive styles (Bloem, 1973; Dixon, et al., 1984; Hansen, 1984; Sackeim, et al., 1977; Shevrin, 1984). O n the other hand, stimulus variables obviously also influence the way an individual may react; these may include depth of subliminality, order of presentation relative to supraliminal stimuli, length and number of stimuli, as well as emotional content (Bloem, 1973; Hansen, 1984; Shevrin, 1984). Baird and Wilding (1980, cited by Dixon, 1981) found that the use of subliminal verbal reinforcers, "good" and "bad" upon judging the lengths of supralirninal lines, were only effective with extraverts and had no effect on introverts. However, subliminal sensitivity has not yet been extensively studied and little has been done on the ~ossiblepersonality correlates of subliminal susceptibility. The aim of the present study was to investigate the possible
SUBLIMINAL STIMULATION AND CHOICE BEHAVIOR
3 17
relationship between specific personality variables and the effect of subliminal stimulation on choice behavior. Because little is known about susceptibility to subliminal perception, some cues had to be taken from research on hypnotizabhty. According to Meichenbaum and Gilrnore (cited by Bowers & Meichenbaum, 1984) both subliminal perception and the hypnotic state are examples of the concept of unconscious events. Accordingly, it was found that emotionally stable subjects with low anxiety and an external locus of control were more susceptible to hypnotic induction (Barber, 1956; Levitt & Persky, 1962; Souheaver & Schuldt, 1978). It was, therefore, hypothesized that subjects who show low anxiety, less neuroticism, an external locus of control, and the trait of extraversion would be more susceptible to subliminal stimulation. METHOD Subjects Thirty-eight undergraduate students (17 men and 21 women) were selected from 5 5 volunteers to participate in the study (mean age, 22.6 yr.). Persons with hearing deficits and psychiatric problems were excluded. Only subjects showing the general trait of right hemisphericity, as indicated by direction of eye movement upon interrogation (Day, 1967) were included (Sackeim, et al., 1977). Apparatus Subliminal stimulation was delivered by means of a Becker Mark 111-B audiosubliminal processor. Two separate taped sets of subliminal stimuli were prepared. The fust set, constructed for the establishment of individual thresholds, consisted of nine emotional and nine neutral words, with 5-sec. intervals between words. The second set consisted of nine short messages; three or four words administered every 20 sec. urging subjects to choose symbols, e.g., "I prefer symbols," "Choose symbols," or "Ignore numbers." Assessment Instruments The IPAT Anxiety Scale is a 14-item self-report inventory, designed to measure free-floating manifest anxiety (Cattell, Scheier, & Madge, 1968). Rotrer's Internal-External Locus of Control Scale consists of 23 question-pairs, using a forced-choice format, plus six filler questions, and provides a measure of whether a person perceives events as contingent upon his behavior or characteristics (Rotter, 1966). Adequate reliability and validity for this scale has been reported by Robinson and Shaver (1973) and Rotter (1966). The Eysenck Personahty Inventory consists of 57 items and measures two dimensions of personality, Neuroticism and Introversion-extraversion (Eysenck & Eysenck, 1964).
As the subliminal messages were meant to influence choice behavior, a choice task had to be designed to measure overt choice behavior. The choice task consisted of 48 symbols, 48 numbers and 48 letters, randomly selected and randomly assigned to 12 columns on a sheet of paper. Several trials on which a group of graduate students were requested to mark any 50 characters showed that no patterns were recognized. Scores on the choice task were ascertained by separately counting the numbers, symbols, and letters marked during each completion of the choice task.
Procedure Upon selection, subjects attended a group session during which they were briefed on the aim of the study and the experimental procedure. The equipment used was also described. Written consent for their participation was also obtained. At the beginning and again at the end of the session subjects completed the choice task. They were instructed to mark, as quickly as possible, any 5 0 characters on the answer sheet. During this session subjects also completed the IPAT Anxiety Scale, I-E Scale, and Eysenck's inventory. Each subject then came individually to the laboratory for nine sessions, three per week, two days apart, that followed a similar sequence and lasted about 15 min. each. At the beginning of the first experimental session subjects again completed the choice task. This measurement, combined with the two obtained during the group session, was used to calculate a mean pretest measurement for each subject. The choice task was completed again at the end of the third, sixth, and ninth sessions, yielding a mean subliminal stimulation measurement for each subject directly after stimulation. During each experimental session, the individual threshold was determined by means of the taped emotional and neutral words, masked by 45-dB white noise. The Method of Limits was used, with nonverbal yeslno-responses i n both ascending and descending order. Each such stimulus was alternated with a 0-dB stimulus for control purposes. The mean of the ascending and descending thresholds was used as the subject's threshold for that specific session. The subliminal processor was adjusted an additional 3 dB below the threshold for each subject. The subliminal message (preference for symbols), again masked by 45-dB white noise, were then presented. Approximately 90 messages were presented during each session. No subject reported hearing any stimulus when asked at the end of each session. Subjects attended a group session six weeks after the final experimental session, during which their enquiries were dealt with, and they were remunerated for their participation. At the beginning, during, and at the end of this session the choice task was again completed, yielding a mean posttest measurement for each subject.
3 19
SUBLIMINAL STIMULATION AND CHOICE BEHAVIOR
RESULTS Mean choices of symbols, letters, and numbers before, during, and after subliminal stimulation, are presented in Table 1. To evaluate whether subliminal stimulation had any effect on the choice of symbols, letters or numbers, the General Linear Models procedure (Roscoe, 1975) was used. This analysis showed that no significant differences occurred [F,,,,, (symbols) = 0.41, p = .67; F,,,,, (numbers) = 0.59, p = .55; F,,,,, (letters) = 0.47, p = .62]. Also no significant difference was found between symbol choices before and during subliminal stimulation (t,, = 0.01, p = .99) or symbol choice before and after subliminal stimulation (t,, = 1.41, p = .16). TABLE 1
Choice
Time
M
SD
Symbols
Before
19.5 19.5 18.1
6.2
9.3
15.6 14.7 16.2
4.5 5.5 7.6
15.2 15.7 16.9
5.7 6.9 10.1
During
Letters
Numbers
After Before During After Before During After
7.6
As these results showed that subliminal stimulation did not affect the choice of symbols significantly, it was decided to assess whether differences in person&ty ratings might exist between those subjects for whom symbol choice increased after subliminal stimulation and those for whom no increase occurred. Means, standard deviations, and ranges of scores of the personality measures are shown in Table 2. TABLE 2 MEANS,STANDARD DEVIATIONS, AND RANGES OF SCORES ON PERSONALITY MEASURES (N= 38) Personality Measure Locus of Control Neuroticism Introversion-Extraversion Anxiety
Range 18-3 20-1
20-8 50-7
M 10.1 10.9 13.9 26.5
SD 3.7 4.7
3.3 11.2
According to the symbol choice before and during subliminal stimulation (Diff. 1) and symbol choice before and 6 wk. after subliminal stimulation (Diff. 2), subjects were divided into three subgroups: Group 1 (Q, and below), Group 2 (Q, to Q,), and Group 3 (above Q,). Group 1 consisted of
subjects who showed little reaction to subliminal stimulation (n = 10 for Diff. 1 and n = 8 for Diff. 2), Group 3 those who showed marked reaction (ns = 9 and 8 for Diffs. 1 and 2, respectively) and Group 2 those in between (ns = 19 and 22). To test the hypothesis that subliminal effects would be associated with personality variables, the personality scores of the three subgroups were compared by means of the General Linear Models procedure. The results are shown in Table 3. No differences were found among these subgroups, indicating that the choice of symbols during or after subliminal stimulation was not associated with personality variables chosen for this study. TABLE 3 COMPARISON OF PERSONALITY SCORES OF SUBGROUPS ACCORDING TO SYMBOL CHOICEBEFOREAND DURINGSUBLIMINAL STIMULATION ( D m . 1) A N D BEFOREAND A ~ SUBLIMINAL R STIMULATION ( D m . 2) Diff. 1
Personality Measure Locus of Control Neuroticism Introversion-Extraversion Anxiety
Diff. 2
F
P
F
P
1.55 0.51 1.93 0.20
.23 .60 .16 .82
0.70 0.05
.50 .95 .13 .22
2.15 1.56
DISCUSSION The results showed that subliminal messages urging subjects to choose symbols instead of numbers or letters did not generate a preference for symbols above letters and numbers. No evidence was found to reject the hypothesis that subliminal stimulation has no effect on overt choice behavior. No results were found in spite of the fact that the subliminal messages used in the present study were in the imperative as suggested by Zuckerman (1960). Similarly, no support was observed for the hypothesis that personality variables such as anxiety, neuroticism, locus of control, and introversion-extraversion may be associated with susceptibility to the type of subliminal stimulation investigated. A possible explanation for these results may be found in the content of the subliminal messages used, as suggested by Shevrin (1984). Choice of symbols, employed in the present study, represents a rather neutral and subjectively meaningless assignment that did not relate to the subjects' needs or motivation. With such a psychodynamically irrelevant message, it may be likely that subliminal stimulation will be less effective and that stable person&ty dispositions such as extraversion or locus of control will exert less influence on susceptibility to subliminal stimulation. That no association between the selected personality variables and susceptibility was found cannot simply be regarded as evidence that no such
SUBLIMINAL STIMULATION AND CHOICE BEHAVIOR
32 1
relationship exists. I t seems important that studies of susceptibility match the content of the subliminal messages carefully to the psychodynamics of the subjects. Then one may assess whether susceptibility to subliminal stimulation is relared to personality variables, as tentative reports in the literature have suggested (Dixon, 1981). REFERENCES ALISON,J. (1963) Cognitive structure and receptivity to low-intensity stimulation. Journal of Abnormal and Social Psychology, 67, 132-138. BARBER,T. X. (1956) A note on "hypnotizab~lity" and personality traits. lournal of Clinical and Experimental Hypnosis, 4, 109-114. BLOEM,S. J. P (1973) 'n Empiriese ondersoek no die invloed van subliminale prikkels by die oordrag van inligting. [An empirical investigation into the effect of subliminal stimuli on the transfer of information.] Unpublished master's thesis, Univer. of South Africa, Pretoria. BYRNE,D. (1959) The effects of a subliminal food stimulus on verbal responses. Journal of Applied Psychology, 43, 249-252. CAT~ELL, R. B., SCPLEIER, I. H., & MADGE,E. M. (1968) Handleiding vir die IPAT-angsskaal. [Manual of the IPAT Anxiety Scale.] Pretoria: National Bureau for Educational and Social Research. DAY, M. E. (1967) An eye-movement indicator of individual differences in the physiological organization of attentional processes and anxiety. lournal of Psychology, 66, 51-62. DIXON,N. F. (1971) Subliminal perception: the nature of a controversy. New York: McGraw-
W.
DIXON,N. F. (1981) Preconscious processing. New York: Wiley. DIXON,N. F,, HENTSCHEL, U., & SMITH,G. (1984) Subliminal perception and microgenesis in the context of personality research. (Unpublished manuscript) EAGLE,M. (1962) Personality correlates of sensitivity to subliminal stimulation. lournal of Nervous and Mental Disease, 134, 1-17. H. J., & EYSENCK,S. B. G. (1964) Manual of the Eysenck Personality Inventory. EYSENCK, London: Univer. of London Press. GOUISTEM,M. J., & BARTHOL, R. I? (1960) Fantasy responses to subliminal stimuli. lournal of Abnormal and Social Psychology, 60, 22-26. GOLDSTEM,M. J., & DAVIS,D. (1961) The impact of stimuh reg~sreringoutside of awareness upon personal preferences. lournal of Personality, 29, 247-257 HANSEN,P. (1984) Subliminal perception. Paper presented at the conference of the International Motivation Corporation, Canberra, Australia. L ~ v r r r ,E. E., & PERSKY,H . (1962) Experimental evidence for the validity of the IPAT Anxiety Scale. Journal of Clinical Psychology, 18, 458-461. MEICFIENBAUM, D., & GILMORE,J. B. (1984) The nature of unconscious processes: a cognitive-behavioral perspective. In K. S. Bowers & D. Meichenbaum (Eds.), The unconscious reconsidered. New York: Wiley. Pp. 273-298. MURCH,G. M. (1969) Responses to incidental stimuli as a function of feedback contingency. Perception 6 Psychophysics, 5 , 10-12. R o e m s o ~ J. , P, & SFLAVER, I? R. (1973) Measures of social psychological attitudes. Ann Arbor, MI: Survey Research Center. ROSCOE,J. T. (1975) Fundamental research statistics for the behavioral sciences. New York: Holt, Rinehart & Winston. R o ~ RJ., B. (1966) Generalised ex ectancies for internal versus external control of reinforce, No. 1 (Whole No. 609). ment. Psychological ~ o n o g r a p E 80, SACKEIM,H . A., PACKER,I. K., & GUR,R. C. (1977) Hemisphericity, cognitive set, and susceptibility to subliminal perception. Journal ofAbnorma1 Psychology, 86, 624-630. SHERROD, D. R. (1972) Lateral eye movements and reaction to persuasion. Perceptual and Motor Skills.. 35,. 355-358. SHE-, H. (1984) Subliminal perception and subliminal communication technology. Invited
testimony presented at the meeting of the Science and Technology Subcommittee on Transportation, Aviation and Mater~als,University of Michigan. SOUHEAVER, G. T., & SCHULLIT,W. J. (1978) Effects of differences in suggestibility within self- and external-control conditions lournal of Consulting and Clinical Psychology, 46, 1230-1233. ZUCKERMAN, M. (1960) The effects of subliminal and supraliminal suggestion on verbal productivity. Journal of Abnormal and Social Psychology, 60, 404-411.
Accepted February 11, 1391.
SUBLIMINAL STIMULATION, CHOICE BEHAVIOR AND SOME PERSONALITY CORRELATES O F SUBLIMINAL SENSITIVITY ' HENDRIK F. KOTZE Unit for Clinical Psychology University of Stellenbo~cb
AND
ANDRE T. MOLLER UniuersiQ of Stellenbosch
Summary.-The aim of this study was to investigate the possible relations between specific personality variables and the effect of subliminal stimulation on choice behavior. It was hypothesized that subjects with low anxiety, less neuroticism, and external locus of control and the trait of extraversion would be more susceptible to subliminal stimulation, 38 undergraduate students were exposed to subliminal messages urging them to choose symbols instead of numbers or letters. Analysis showed that subliminal stimulation did not generate a preference for symbols over numbers or letters. No support was observed for the hypothesis of an association between susceptibility and personality variables. These results may be explained in terms of symbol choice being a neutral message that did not relate to the subjects' needs and motivation.
A review of the literature on subliminal perception by Dixon (1981) has demonstrated that the phenomenon as such does indeed exist; however, as far as choice behavior is concerned, Dixon (1971) concluded that ". . . the evidence suggests that, whereas verbal behaviour can be affected by subliminal stimuli, these may have little effect upon other overt acts of choice" (p. 176). Dixon based his conclusion on studies by Byrne (1959), Goldstein and Barthol (1960), and Goldstein and Davis (1961) which suggested that, while "stimulus registration without awareness serves to modify or increase subjects' level of motivation or arousal . . . the overt behaviour which occurs in response to the increased motivation will be more closely related to subjects' past history of reducing this motivation" (Goldstein & Davis, 1961, p. 254). The question arises as to whether the effect of subliminal stimulation on choice behavior might be related to personality variables. Since Eagle (1962) suggested that some subjects are more sensitive to the effects of subliminal stimuli than others, various studies investigated the susceptibility to subliminal stimulation. A review of the factors related to the appearance and strength of sublirninal effects suggests that individual differences in hemisphericity are associated with the strength of subliminal perception. Several researchers showed that a relaxed rather than a focally alert state of mind increases sensitivity to subliminal stimulation (Bloem, 1973; Dixon, Hentschel, & Smith, 1984; Eagle, 1962; Murch, 1969). Eagle (1962) noted 'Requests for reprints should be addressed to Hendrik F. Kotzi, Unit for Clinical Psychology, University of Stellenbosch, Stellenbosch 7600, South Africa.
that subjects high and low in sensitivity showed different cognitive styles, which he described in terms of the following dimensions: (1) receptivity to inner cues, (2) ability to relax cognitive controls, and (3) style of attention deployment. Similarly, a study of Alison (1963) showed that, when subjects were encouraged to think intuitively, globally and freely, subliminal effects were demonstrated. No effects were found when they were encouraged to thlnk in organized, analytic, and logical modes. Murch (1969) also found that subjects who used intuitive strategies showed greater subliminal effects than those subjects who used an analytical approach. Similar results were reported by Hansen (1984) and Sherrod (1972). Sackeim, Packer, and Gur (1977) suggested that the terms used to describe the characteristics of individuals who appear to differ in susceptibility to subliminal perception, are similar to those used to characterize individuals who differ in hemisphericity. Their study indicated that the effect of subliminal cues upon perception of a neutral face is significantly more pronounced in subjects showing the general trait of right hemisphericity, as indicated by direction of eye movement upon interrogation (Day, 1967). They also found that a relaxed state favoured subliminal perception of the neutral face but again this was only true of the subjects with right hemisphericity. These results, indicating that hemisphericity and cognitive set interact in producing subliminal effects, led Dixon (1981, p. 34) to conclude: "Evidently low arousal, as well as right hemisphericity, makes for susceptibfity to stimuli below the awareness threshold." Other variables associated with susceptibility to subliminal stimulation have also been described in the literature. Shevrin (1984), for example, stressed the relationship between the type of stimulus presented and the motivational state of the observer. The same stimulus might evoke a wide range of reactions from different individuals; the process of perception is highly idiosyncratic and is coloured by factors like the individual's needs, values, emotional state, defence mechanisms and cognitive styles (Bloem, 1973; Dixon, et al., 1984; Hansen, 1984; Sackeim, et al., 1977; Shevrin, 1984). O n the other hand, stimulus variables obviously also influence the way an individual may react; these may include depth of subliminality, order of presentation relative to supraliminal stimuli, length and number of stimuli, as well as emotional content (Bloem, 1973; Hansen, 1984; Shevrin, 1984). Baird and Wilding (1980, cited by Dixon, 1981) found that the use of subliminal verbal reinforcers, "good" and "bad" upon judging the lengths of supralirninal lines, were only effective with extraverts and had no effect on introverts. However, subliminal sensitivity has not yet been extensively studied and little has been done on the ~ossiblepersonality correlates of subliminal susceptibility. The aim of the present study was to investigate the possible
SUBLIMINAL STIMULATION AND CHOICE BEHAVIOR
3 17
relationship between specific personality variables and the effect of subliminal stimulation on choice behavior. Because little is known about susceptibility to subliminal perception, some cues had to be taken from research on hypnotizabhty. According to Meichenbaum and Gilrnore (cited by Bowers & Meichenbaum, 1984) both subliminal perception and the hypnotic state are examples of the concept of unconscious events. Accordingly, it was found that emotionally stable subjects with low anxiety and an external locus of control were more susceptible to hypnotic induction (Barber, 1956; Levitt & Persky, 1962; Souheaver & Schuldt, 1978). It was, therefore, hypothesized that subjects who show low anxiety, less neuroticism, an external locus of control, and the trait of extraversion would be more susceptible to subliminal stimulation. METHOD Subjects Thirty-eight undergraduate students (17 men and 21 women) were selected from 5 5 volunteers to participate in the study (mean age, 22.6 yr.). Persons with hearing deficits and psychiatric problems were excluded. Only subjects showing the general trait of right hemisphericity, as indicated by direction of eye movement upon interrogation (Day, 1967) were included (Sackeim, et al., 1977). Apparatus Subliminal stimulation was delivered by means of a Becker Mark 111-B audiosubliminal processor. Two separate taped sets of subliminal stimuli were prepared. The fust set, constructed for the establishment of individual thresholds, consisted of nine emotional and nine neutral words, with 5-sec. intervals between words. The second set consisted of nine short messages; three or four words administered every 20 sec. urging subjects to choose symbols, e.g., "I prefer symbols," "Choose symbols," or "Ignore numbers." Assessment Instruments The IPAT Anxiety Scale is a 14-item self-report inventory, designed to measure free-floating manifest anxiety (Cattell, Scheier, & Madge, 1968). Rotrer's Internal-External Locus of Control Scale consists of 23 question-pairs, using a forced-choice format, plus six filler questions, and provides a measure of whether a person perceives events as contingent upon his behavior or characteristics (Rotter, 1966). Adequate reliability and validity for this scale has been reported by Robinson and Shaver (1973) and Rotter (1966). The Eysenck Personahty Inventory consists of 57 items and measures two dimensions of personality, Neuroticism and Introversion-extraversion (Eysenck & Eysenck, 1964).
As the subliminal messages were meant to influence choice behavior, a choice task had to be designed to measure overt choice behavior. The choice task consisted of 48 symbols, 48 numbers and 48 letters, randomly selected and randomly assigned to 12 columns on a sheet of paper. Several trials on which a group of graduate students were requested to mark any 50 characters showed that no patterns were recognized. Scores on the choice task were ascertained by separately counting the numbers, symbols, and letters marked during each completion of the choice task.
Procedure Upon selection, subjects attended a group session during which they were briefed on the aim of the study and the experimental procedure. The equipment used was also described. Written consent for their participation was also obtained. At the beginning and again at the end of the session subjects completed the choice task. They were instructed to mark, as quickly as possible, any 5 0 characters on the answer sheet. During this session subjects also completed the IPAT Anxiety Scale, I-E Scale, and Eysenck's inventory. Each subject then came individually to the laboratory for nine sessions, three per week, two days apart, that followed a similar sequence and lasted about 15 min. each. At the beginning of the first experimental session subjects again completed the choice task. This measurement, combined with the two obtained during the group session, was used to calculate a mean pretest measurement for each subject. The choice task was completed again at the end of the third, sixth, and ninth sessions, yielding a mean subliminal stimulation measurement for each subject directly after stimulation. During each experimental session, the individual threshold was determined by means of the taped emotional and neutral words, masked by 45-dB white noise. The Method of Limits was used, with nonverbal yeslno-responses i n both ascending and descending order. Each such stimulus was alternated with a 0-dB stimulus for control purposes. The mean of the ascending and descending thresholds was used as the subject's threshold for that specific session. The subliminal processor was adjusted an additional 3 dB below the threshold for each subject. The subliminal message (preference for symbols), again masked by 45-dB white noise, were then presented. Approximately 90 messages were presented during each session. No subject reported hearing any stimulus when asked at the end of each session. Subjects attended a group session six weeks after the final experimental session, during which their enquiries were dealt with, and they were remunerated for their participation. At the beginning, during, and at the end of this session the choice task was again completed, yielding a mean posttest measurement for each subject.
3 19
SUBLIMINAL STIMULATION AND CHOICE BEHAVIOR
RESULTS Mean choices of symbols, letters, and numbers before, during, and after subliminal stimulation, are presented in Table 1. To evaluate whether subliminal stimulation had any effect on the choice of symbols, letters or numbers, the General Linear Models procedure (Roscoe, 1975) was used. This analysis showed that no significant differences occurred [F,,,,, (symbols) = 0.41, p = .67; F,,,,, (numbers) = 0.59, p = .55; F,,,,, (letters) = 0.47, p = .62]. Also no significant difference was found between symbol choices before and during subliminal stimulation (t,, = 0.01, p = .99) or symbol choice before and after subliminal stimulation (t,, = 1.41, p = .16). TABLE 1
Choice
Time
M
SD
Symbols
Before
19.5 19.5 18.1
6.2
9.3
15.6 14.7 16.2
4.5 5.5 7.6
15.2 15.7 16.9
5.7 6.9 10.1
During
Letters
Numbers
After Before During After Before During After
7.6
As these results showed that subliminal stimulation did not affect the choice of symbols significantly, it was decided to assess whether differences in person&ty ratings might exist between those subjects for whom symbol choice increased after subliminal stimulation and those for whom no increase occurred. Means, standard deviations, and ranges of scores of the personality measures are shown in Table 2. TABLE 2 MEANS,STANDARD DEVIATIONS, AND RANGES OF SCORES ON PERSONALITY MEASURES (N= 38) Personality Measure Locus of Control Neuroticism Introversion-Extraversion Anxiety
Range 18-3 20-1
20-8 50-7
M 10.1 10.9 13.9 26.5
SD 3.7 4.7
3.3 11.2
According to the symbol choice before and during subliminal stimulation (Diff. 1) and symbol choice before and 6 wk. after subliminal stimulation (Diff. 2), subjects were divided into three subgroups: Group 1 (Q, and below), Group 2 (Q, to Q,), and Group 3 (above Q,). Group 1 consisted of
subjects who showed little reaction to subliminal stimulation (n = 10 for Diff. 1 and n = 8 for Diff. 2), Group 3 those who showed marked reaction (ns = 9 and 8 for Diffs. 1 and 2, respectively) and Group 2 those in between (ns = 19 and 22). To test the hypothesis that subliminal effects would be associated with personality variables, the personality scores of the three subgroups were compared by means of the General Linear Models procedure. The results are shown in Table 3. No differences were found among these subgroups, indicating that the choice of symbols during or after subliminal stimulation was not associated with personality variables chosen for this study. TABLE 3 COMPARISON OF PERSONALITY SCORES OF SUBGROUPS ACCORDING TO SYMBOL CHOICEBEFOREAND DURINGSUBLIMINAL STIMULATION ( D m . 1) A N D BEFOREAND A ~ SUBLIMINAL R STIMULATION ( D m . 2) Diff. 1
Personality Measure Locus of Control Neuroticism Introversion-Extraversion Anxiety
Diff. 2
F
P
F
P
1.55 0.51 1.93 0.20
.23 .60 .16 .82
0.70 0.05
.50 .95 .13 .22
2.15 1.56
DISCUSSION The results showed that subliminal messages urging subjects to choose symbols instead of numbers or letters did not generate a preference for symbols above letters and numbers. No evidence was found to reject the hypothesis that subliminal stimulation has no effect on overt choice behavior. No results were found in spite of the fact that the subliminal messages used in the present study were in the imperative as suggested by Zuckerman (1960). Similarly, no support was observed for the hypothesis that personality variables such as anxiety, neuroticism, locus of control, and introversion-extraversion may be associated with susceptibility to the type of subliminal stimulation investigated. A possible explanation for these results may be found in the content of the subliminal messages used, as suggested by Shevrin (1984). Choice of symbols, employed in the present study, represents a rather neutral and subjectively meaningless assignment that did not relate to the subjects' needs or motivation. With such a psychodynamically irrelevant message, it may be likely that subliminal stimulation will be less effective and that stable person&ty dispositions such as extraversion or locus of control will exert less influence on susceptibility to subliminal stimulation. That no association between the selected personality variables and susceptibility was found cannot simply be regarded as evidence that no such
SUBLIMINAL STIMULATION AND CHOICE BEHAVIOR
32 1
relationship exists. I t seems important that studies of susceptibility match the content of the subliminal messages carefully to the psychodynamics of the subjects. Then one may assess whether susceptibility to subliminal stimulation is relared to personality variables, as tentative reports in the literature have suggested (Dixon, 1981). REFERENCES ALISON,J. (1963) Cognitive structure and receptivity to low-intensity stimulation. Journal of Abnormal and Social Psychology, 67, 132-138. BARBER,T. X. (1956) A note on "hypnotizab~lity" and personality traits. lournal of Clinical and Experimental Hypnosis, 4, 109-114. BLOEM,S. J. P (1973) 'n Empiriese ondersoek no die invloed van subliminale prikkels by die oordrag van inligting. [An empirical investigation into the effect of subliminal stimuli on the transfer of information.] Unpublished master's thesis, Univer. of South Africa, Pretoria. BYRNE,D. (1959) The effects of a subliminal food stimulus on verbal responses. Journal of Applied Psychology, 43, 249-252. CAT~ELL, R. B., SCPLEIER, I. H., & MADGE,E. M. (1968) Handleiding vir die IPAT-angsskaal. [Manual of the IPAT Anxiety Scale.] Pretoria: National Bureau for Educational and Social Research. DAY, M. E. (1967) An eye-movement indicator of individual differences in the physiological organization of attentional processes and anxiety. lournal of Psychology, 66, 51-62. DIXON,N. F. (1971) Subliminal perception: the nature of a controversy. New York: McGraw-
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DIXON,N. F. (1981) Preconscious processing. New York: Wiley. DIXON,N. F,, HENTSCHEL, U., & SMITH,G. (1984) Subliminal perception and microgenesis in the context of personality research. (Unpublished manuscript) EAGLE,M. (1962) Personality correlates of sensitivity to subliminal stimulation. lournal of Nervous and Mental Disease, 134, 1-17. H. J., & EYSENCK,S. B. G. (1964) Manual of the Eysenck Personality Inventory. EYSENCK, London: Univer. of London Press. GOUISTEM,M. J., & BARTHOL, R. I? (1960) Fantasy responses to subliminal stimuli. lournal of Abnormal and Social Psychology, 60, 22-26. GOLDSTEM,M. J., & DAVIS,D. (1961) The impact of stimuh reg~sreringoutside of awareness upon personal preferences. lournal of Personality, 29, 247-257 HANSEN,P. (1984) Subliminal perception. Paper presented at the conference of the International Motivation Corporation, Canberra, Australia. L ~ v r r r ,E. E., & PERSKY,H . (1962) Experimental evidence for the validity of the IPAT Anxiety Scale. Journal of Clinical Psychology, 18, 458-461. MEICFIENBAUM, D., & GILMORE,J. B. (1984) The nature of unconscious processes: a cognitive-behavioral perspective. In K. S. Bowers & D. Meichenbaum (Eds.), The unconscious reconsidered. New York: Wiley. Pp. 273-298. MURCH,G. M. (1969) Responses to incidental stimuli as a function of feedback contingency. Perception 6 Psychophysics, 5 , 10-12. R o e m s o ~ J. , P, & SFLAVER, I? R. (1973) Measures of social psychological attitudes. Ann Arbor, MI: Survey Research Center. ROSCOE,J. T. (1975) Fundamental research statistics for the behavioral sciences. New York: Holt, Rinehart & Winston. R o ~ RJ., B. (1966) Generalised ex ectancies for internal versus external control of reinforce, No. 1 (Whole No. 609). ment. Psychological ~ o n o g r a p E 80, SACKEIM,H . A., PACKER,I. K., & GUR,R. C. (1977) Hemisphericity, cognitive set, and susceptibility to subliminal perception. Journal ofAbnorma1 Psychology, 86, 624-630. SHERROD, D. R. (1972) Lateral eye movements and reaction to persuasion. Perceptual and Motor Skills.. 35,. 355-358. SHE-, H. (1984) Subliminal perception and subliminal communication technology. Invited
testimony presented at the meeting of the Science and Technology Subcommittee on Transportation, Aviation and Mater~als,University of Michigan. SOUHEAVER, G. T., & SCHULLIT,W. J. (1978) Effects of differences in suggestibility within self- and external-control conditions lournal of Consulting and Clinical Psychology, 46, 1230-1233. ZUCKERMAN, M. (1960) The effects of subliminal and supraliminal suggestion on verbal productivity. Journal of Abnormal and Social Psychology, 60, 404-411.
Accepted February 11, 1391.
