Modern Psychological Studies

Volume 1 Number 1 Article 7

1992

Subliminal and the Stroop effect

Sandra Harvey Baylor University

Shannon Keathley Baylor University

Delinda Muniz Baylor University

Ginger Tidmore Baylor University

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Recommended Citation Harvey, Sandra; Keathley, Shannon; Muniz, Delinda; and Tidmore, Ginger (1992) "Subliminal perception and the Stroop effect," Modern Psychological Studies: Vol. 1 : No. 1 , Article 7. Available at: https://scholar.utc.edu/mps/vol1/iss1/7

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Subliminal Perception and the was the first to use this task, and he demonstrated the Stroop effect. This effect Stroop Effect refers to a disruption in the rate of naming a Sandra Harvey, Shannon Keathley, color when the color is presented in the Delinda Muniz, and Ginger Tidmore form of another word. For example, the Stroop effect is demonstrated when a Baylor University subject is asked to name the color red when the word "blue" is written in red ink. This ABSTRACT creates interference which is due to the subject's inability to separate color The Stroop effect and subliminal information from word information. An perception are two phenomena which have interference score can be computed for a been studied for years. However, the given subject. Since it was first reported in potential relation between the two has not this country by Stroop(1935), there have been conclusively explored. This been numerous studies conducted on how experiment was designed to demonstrate changing various components of the test that a relationship between the two may affects a subject's given score. exist. The procedure consisted of Klein(1964) conducted a very important subliminally presenting the name of a color study which involved varying the verbal written in black letters simultaneously with texts in which four colors were presented. a colored stimulus. The supraliminal He found that the Stroop Test does show colored stimulus and subliminal word interference which is maximized by stimulus were presented on a screen by use incongruent word/color pairs. of a projector and a tachistoscope (t-scope) One consideration in the S troop respectively. It was hypothesized that effect is environmental control. The subliminal perception would create elimination of distracting environmental interference on the projected Stroop Test aspects may result in a quicker reaction simulating a Stroop effect. Statistical time. Cohen, Dunbar, and McClelland analysis of the data showed a significant report that less environmental distraction increase in reaction times on the projected yields more automatic responses, which is Stroop test indicating a possible subliminal the preferred condition(1990). However, interference. No correlation was found Francolini and Egeth(1980) minimize the between the percent increases in reaction importance of this consideration by stating times between the paper test and the that it is not possible to control the projected test. environment enough to have a significant decrease in reaction times. INTRODUCTION A second consideration with the Stroop effect is . It is evident that This study examined the effects of the cognitive battle between color naming subliminal perception on the S troop effect. and word reading results in a much slower Many studies have been conducted in these response (Dyer,1973). Therefore, a areas, but those of most relevance to this practicing of these processes should result study involve visual subliminal effects and in faster reaction times. However, there is Stroop effects. This study was concerned evidence that this is not the case. Driver and with determining if subliminal perception Tipper (1989) found that word reading is an could cause a Stroop interference effect. automatic reaction and color naming is a Because of the different nature of these two controlled reaction. This resulted in word concepts, they are discussed individually reading dominating color matching because and then an integration of the two is it was the key factor in the learning process. introduced. The authors concluded that once a certain The Stroop Color-Word Test deals level of learning is attained, the effect will with cognitive processes that are involved be greatly reduced resulting in a in naming colors and reading words. stabilization and plateau in reaction time. Schiller(1966) notes that Jaensch(1929) Even though learning may play a part to this

MODERN PSYCHOLOGICAL STUDIES 28 SUBLIMINAL PERCEPTION AND THE STROOP EFFECT extent, it is counteracted by a drop in the effects. In essence, it is believed that people subject's due to fatigue and other do perceive on a subliminal level. factors (Driver & Tipper, 1989). There are still many issues in Subliminal perception presents its studying subliminal perception and its own unique considerations as well as a effects. One issue concerns how awareness controversial history. The initial debate over is operationalized, which effects the subliminal perception concerned marketing. determination of the threshold value. There A study by Vicary (1957) cited in is a subjective and an objective operational Wortman, Loftus, & Marshall (1992) definition of this variable. The subjective suggested that people could be persuaded definition consists of using the method of by subliminal messages to buy Coke and limits and has the subject determine whether popcorn. This started a controversy because or not he/she is aware of a stimulus people did not like the idea that they could (Holender, 1986). This is a questionable be behaviorally manipulated without their way of operationalizing the variable because awareness. However, many people were it gives the responsibility of very interested in using this phenomenon operationalizing awareness to the subject especially in marketing and as a means of rather than to the experimenter (Merikle, behavioral control. 1981; Moore, 1989). According to Dixon (cited in On the other hand, there is an Groeger, 1984) three criterion must be met objective way to operationalize awareness to ensure a subliminal presentation. The which was first proposed by Eriksen first is that the stimulus must be presented (1960) cited in Miller (1991). "Awareness at a level below the lowest level where the is defined in terms of an observer's ability subject can identify the stimulus. The to discriminate among several possible second criteria is that the subject should stimulus states as indicated by verbal never report any detection of the stimulus. reports in forced-choice tasks" (Merikle, Finally, when a stimulus is presented 1984). This definition is preferred and is a subliminally, the effects of the stimulus major reason why the more recent research presentation should be different from the regarding priming studies with subliminal effects of presenting the supraliminal perception have had a more persuasive stimulus. impact than past studies concerning this Many studies have been conducted phenomenon (Merikle, 1984). providing evidence that subliminal A second difficulty with subliminal perception occurs on a tactual, visual, and perception experiments is that it is very auditory level, but only under carefully difficult to determine what the threshold of controlled laboratory conditions (Wortman the subject is. One problem with this is that et. al., 1992; Robles, Smith, Carver, & the threshold will vary from one subject to Wellens, 1987, cited in Laird & Thompson, another and within one subject over the 1992). There has not been evidence that course of the experiment. Therefore, the subliminal perception can be used to control stimulus must be below the threshold an individual's behavior (Wortman et. al., enough to remain undetected during these 1992). fluctuations. However, it must also not be More evidence of visual subliminal so low that it cannot even be perceived perception concerns priming studies. subliminally. This has posed great difficulty Priming studies subliminally present a in many of the studies. prime word such as "nurse" which is A third issue in subliminal similar in content to a target word such as perception is the question of whether or not "doctor." By presenting a subliminal prime the meaning of a subliminally presented word, subjects are more accurate in word can be discerned by the observer. identifying the supraliminal target word There is evidence that there can be some presented after the subliminal presentation. information perceived when a word is Holender (1986) cites studies by Evett and visually presented below threshold (Allport, Humphreys (1981) and Humphreys, Evett, 1977, cited in Nolan & Caramazza 1982). It and Taylor (1982) that identify priming has also been found that the actual meaning

MODERN PSYCHOLOGICAL STUDIES 29 Sandra Harvey, Shannon Keathley, Delinda Muniz, and Ginger Tidmore of the word rather than its structure may found that there are differences in the have a strong influence over both the subjects' responses when presented with cortical response and the verbal response of subliminal and supraliminal primes; the subject (Begleiter, Gross & Kissin, however, they did not conclude that the 1969, cited in Shevrin & Dickman, 1980). subliminal stimulus functioned sufficiently This may be relevant because the words in as a prime. this study were presented subliminally. If Another similar study by Dyer and the interference is caused by the meaning Severance (1972) cited in Dyer (1973) rather than the structure of the word then addressed the possible role of subliminal the chance of subliminally transferring perception in the demonstration of the meanings is crucial. However, there is also Stroop effect. A subliminal presentation of evidence that it may be the structure of the a word printed in black ink preceded a word rather than its actual meaning which supraliminal presentation of colored Xs. causes interference (Beech, Agar, & Baylis, This study showed that the reaction time in 1989). Overall, it is possible that the naming the color of the Xs was not affected subliminal presentation may yield by any of the preceding subliminal word interference regardless of its meaning. presentations regardless of whether they A fourth consideration concerns the were congruent or incongruent word/color illumination of the stimulus. If the stimulus pairs. Although no Stroop effect occurred, is either too bright or too dark, the their supraliminal presentation of the subliminal word may not be picked up at all colored Xs occurred with 50 msec of Heilburn (1982) cited in Fudin (1987), exposure. Since the subliminal exposure reported that higher illuminated stimuli had was most likely under 50 msec, it could a higher chance of registering with the have been so far below threshold that it may subject than did low illuminated stimuli. not have been detected on any cognitive Therefore, adaptation of the subject was of level and would have no effect. consideration. The judgment of the present Although these studies were unable stimulus is dependent on the adaptation of to substantiate that subliminal perception the subject to present conditions (Dixon, had any S troop effect, there were some 1971). Therefore, in this study there was a flaws in the studies. The study by need for the subject to have time to adapt to Cheesman and Merikle (1986) did not the lighting conditions of the room. This specifically address this particular issue should have decreased any effects a lack of although they originally intended to do so. adaptation would have had on the subject's As stated previously, the study by Dyer judgments. (1973) most likely used too low of a There are previous studies which stimulus level for the subliminal have attempted to demonstrate a relation presentation. Our study took this between subliminal perception and The information into consideration Stroop Test. As stated previously, however, there have been no conclusive METHOD findings concerning the Stroop effect. One Subjects study performed by Cheesman and Merikle (1986) did attempt to use the S troop Test to Ten psychology students, both determine if a subthreshold stimulus could graduate and undergraduate, at Baylor act as a prime. contrary to the objective University comprised the subject pool. The threshold which was used in our study, researchers questioned the subjects in order they determined that it was necessary in to determine if they possessed normal their study to use a subjective threshold. vision, or corrected-to-normal vision and Their reasoning was that since awareness of normal color vision. Those requiring is a subjective experience, it corrective lenses were instructed to use was better to conduct the experiment at a them. subjective level. In addition, it would allow the subject to have a heightened response. Cheesman and Merikle's study essentially

MODERN PSYCHOLOGICAL STUDIES 30 SUBLIMINAL PERCEPTION AND THE STROOP EFFECT

Apparatus the subject was asked to close his/her eyes for two minutes to help facilitate dark In order to present an adequate adaptation. When his/her eyes were closed, stimulus two projectors were used. One the lights were turned off. The first was a standard slide projector and the other presentation consisted of 30 randomized was a tachistoscope (t-scope). The t-scope word slides (red, green, blue) from the was positioned 19 feet from the screen. The standard projector and a simultaneous standard projector was closer to the screen presentation of 30 blank slides from the t- at 16.5 feet. The t-scope had a shutter speed scope. The subject identified the stimulus of one 25th of a second. For the duration of on the screen by reading the word that the experiment the t-scope had three filter he/she saw on the screen. The second trial slides over the lens in order to reduce the began immediately after the first. The intensity of the light. In addition, the subject was presented 30 colored slides overhead lights were completely turned off (red, green, blue) from the standard in order to insure that the colors would be projector and 30 blank slides from the t- easily discriminated. The subject was seated scope. The subject verbally identified the 2.0 feet to the right of the projector and color presented. The third trial consisted of 14.5 feet from the screen. Thirty color 30 colored slides (red, green, blue) slides (red, green, blue), 30 blank slides, projected onto the screen simultaneously and 30 word slides printed in black (red, with 30 subliminally presented word slides green, blue) were used. In order to maintain (red, green, blue) from the t-scope. The continuity throughout the experiment, the subject verbally identified the colored slide instructions for each trial were taped and presented. The subject, however, was not played back to the subjects by use of a aware of the subliminal word presentation. cassette recorder. A fourth untimed trial was Procedure conducted as a part of the debriefing of the subject. This trial served as a control to The experiment had a within subject ensure that the third trial was actually design. Each subject was tested subliminal. The red color stimulus was individually. Instructions to the subject presented along with the subliminal explained that the experiment was a presentation of 30 word slides (red, green, replication of the Stroop effect. The blue). This yielded a forced-choice experimenters told the subject that it was response (red, green, blue) from the subject necessary to present the standard Stroop stating which word slide he/she test before the actual experiment began in was presented. Subliminal perception was order to familiarize the subject with the ensured by chance performance on this material. After the administration of the trial. standard Stroop test, the subject was Debriefing was done upon the informed that the experimenters would completion of the experiment. The advance the slides from two different experimenters explained to the subject that projectors. The subject was told that the use the test determined if interference increased of two projectors would increase the reaction time. brightness of the stimulus. They RESULTS experienced a flash from each projector. The subject was then told that the projected After the data was reviewed, one third trial differed from the third trial of the second was added to the subject's reaction standard Stroop test because of a lack of time for each error the subject made on a adequate equipment. trial. A one tailed two sample, dependent t- The experiment consisted of three test was performed using the variables from trials each of which were timed the second and third projected trials. These individually. The subject's responses as variables were the subjects' reaction times well as his/her errors were recorded for for the second and third trials. The test each trial. Before the projected trials began, determined a p< .002 which was significant

MODERN PSYCHOLOGICAL STUDIES 31 Sandra Harvey, Shannon Keathley, Delinda Muniz, and Ginger Tidmore at a = .05 (see Table 1). A percent increase Table 3 was computed between the second and third Trial 4: Control Data trial for both the paper and projected Subject Percentage of correct responses versions, and a Pearson product-moment 1 26.7 correlation was computed yielding a value of .036 (see Table 2). By using the data 2 36.7 from trial four, subliminal perception was 3 33.3 confirmed by a mean performance of 4 30.0 31.5% which was less than chance 5 36.7 performance of 33.3% (see Table 3). 6 16.7 7 33.3

Table 1 8 36.7 Reaction Time (seconds): Projected Version 9 36.7 10 26.7 Subject Trial 1 Trial 2 Trial 3 X = 31.3 1 52.05 53.91 55.47 2 55.79 56.88 57.84 DISCUSSION 3 57.79 58.95 59.45 4 53.37 55.66 56.41 Overall, this experiment appears to support the hypothesis that subliminal perception 5 53.51 52.93 56.83 creates interference on a projected Stroop 6 55.07 56.12 57.59 test simulating a Stroop effect. This 7 50.22 52.56 55.26 conclusion is supported by the fact that a 8 59.70 57.66 58.13 subliminal word presentation was insured 9 48.35 49.65 53.72 and. the differences between trials 2 and 3 10 51.86 52.45 54.56 were significant at g < .002. Although the x=53.77 x=54.68 x=56.53 findings of this experiment appeared t-test= a=.05 p‹.002 conclusive, there were technical difficulties involving the slide quality and projector consistency which could be improved Many Table 2 factors could be necessary to elicit the effect Percent Increase in Reaction Times (from Trial 2 to Trial 3) which are actively being investigated. Subject Projected Paper REFERENCES 3 100 2 2 68 Beech, Anthony, Agar, Kirsten, & Baylis, Gordon C. (1989). Reversing 3 1 96 priming while maintaining 4 1 139 nterference. Bulletin of the 5 7 45 Psychonomic Society, 27 (6). 553- 6 3 8 555. 7 5 97 Cheesman, Jim & Merikle, Philip M. 8 1 63 (1986). Distinguishing conscious from unconscious perceptual 9 8 89 processes. Canadian Journal of 10 4 91 Psychology, 40 (4), 343-367. X = 3.5 X = 79.6 Cohen, Jonathan D., Dunbar, Kevin, & RSquare= .036 McClelland, James L. (1990). On processing account of the Stroop effect. Psychological Review. 97 (3), 332-361. Dixon, N. F. (1971). Subliminal Perception: The Nature of a

MODERN PSYCHOLOGICAL STUDIES 32 SUBLIMINAL PERCEPTION AND THE STROOPE)-PECT

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