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Subliminal anchoring: The effects of subliminally presented numbers on probability estimates
Journal of Experimental Social Psychology 42 (2006) 380–387 www.elsevier.com/locate/jesp
Subliminal anchoring: The eVects of subliminally presented numbers on probability estimates 夽 Margreet Reitsma-van Rooijen a,¤, Dancker D. L. Daamen b a
Department of Social Psychology, Vrije Universiteit Amsterdam, van der Boechorststraat 1, 1081 BT Amsterdam, The Netherlands b Department of Social and Organizational Psychology, Leiden University, The Netherlands Received 13 August 2004; revised 28 April 2005 Available online 20 July 2005
Abstract Previous research demonstrated that if attention is paid to a supraliminally presented number, a subsequent quantitative estimate assimilates towards this number (the anchor eVect). One explanation states that this eVect is merely caused by the heightened accessibility level of the anchor value itself. Based on this numeric priming account and generalizing from subliminal priming studies, we expected a short-lived subliminal anchor eVect. We presented participants subliminally with a low or high anchor value (10 or 90) and next they had to estimate the probability of an epidemic. Half of them were pressed to do this quickly. Only under time pressure, a signiWcant anchor eVect emerged. © 2005 Elsevier Inc. All rights reserved. Keywords: Anchoring; Subliminal; Numeric priming
Numerical anchoring is the assimilation of a quantitative estimate towards a previously presented number. In one of the Wrst research demonstrations of this eVect, Tversky and Kahneman (1974) asked people to estimate the percentage of African countries in the United Nations. In one condition they were Wrst asked whether this percentage was higher or lower than 10%. In another condition 10% was replaced by 65%. The estimate of the percentage of African countries assimilated towards the percentage in the Wrst question: in the Wrst condition the median estimate was 25%, in the latter condition it was 45%. This anchor eVect has often been demonstrated in a broad range of quantitative judgments such as general knowledge (Chapman & Johnson, 1999; Jacowitz & Kahneman, 1995; Tversky & Kahneman, 1974; Wilson, 夽 We thank Ap Dijksterhuis for valuable advice, and Henk Aarts and Sander Koole for helpful comments on an earlier draft of this article. * Corresponding author. Fax: +31 (0) 20 5988921. E-mail address: [email protected] (M. Reitsma-van Rooijen).
0022-1031/$ - see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jesp.2005.05.001
Houston, Etling, & Brekke, 1996), probability estimates (Plous, 1989), legal judgment (e.g., Chapman & Bornstein, 1996), pricing decisions (Northcraft & Neale, 1987), and negotiation (Ritov, 1996) (for a recent review, see Mussweiler & Strack, 1999). Anchoring is a strong and robust eVect. Not only laymen are susceptible to anchor eVects but also experts when they give judgments in their Weld of expertise, e.g., accountants (Smith & Kida, 1991), real estate agents (Northcraft & Neale, 1987), and judges (Englich & Mussweiler, 2001). Furthermore, the anchor eVect is diYcult to avoid, even when people are forewarned (Wilson et al., 1996). In most demonstrations of the anchor eVect, the anchoring process is initiated by explicitly asking people to compare a supraliminally presented anchor value to a target. They have, for example, to judge whether the chances of recurrence of an epidemic of pestilence of the lungs in India within a year are lower or higher than 10%. After this comparative judgment, they have to make an absolute judgment in which these chances must be estimated exactly (Daamen, de Vries, & Kesnich, 1996). The
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sequence of a comparative and an absolute judgment has become the dominant paradigm (or as termed by Strack & Mussweiler, 1997, the “standard paradigm”) of anchor research. As a consequence, most of the explanations of the anchor eVect have focused on the role of the comparative judgment in the anchor process in that paradigm. Other ways to introduce the anchor value, which diVer from the standard paradigm, have received relatively little attention. The question is whether this standard paradigm is the only way to obtain an anchor eVect. The standard paradigm consists of a number of elements: an anchor value, which can be perceived as either relevant or irrelevant, a comparative judgment in which the anchor value is presented supraliminally, an absolute judgment and in both judgments a target, which can either be the same or diVerent in both judgments. Maybe not all these elements are needed to obtain an anchor eVect. There are many research examples of strong anchor eVects given a relevant anchor value (e.g., Northcraft & Neale, 1987). However, there is still an anchor eVect if the anchor value is clearly irrelevant, for example, if the anchor value is obviously random, for example, when the anchor value resulted from the spin of a ‘wheel of fortune’ (Tversky & Kahneman, 1974; see also Russo and Shoemaker, 1989, as cited in Chapman & Johnson, 1999) or highly implausible (Mussweiler & Strack, 2001a). Taken together, it appears that both relevant and irrelevant anchor values produce anchor eVects. To account for these anchor eVects, the Selective Accessibility Model (e.g., Strack & Mussweiler, 1997; Mussweiler & Strack, 1999) has been proposed. A fundamental assumption in this model is that one compares the target of the absolute judgment to the anchor value by applying a hypothesis-consistent strategy. As a result the accessibility of anchor-consistent information in memory is heightened. This activation of semantically related information is a crucial part of the Selective Accessibility Model. For example, when it is asked whether the chances for recurrence of the epidemic of pestilence of the lungs are lower or higher than 90%, participants will search for anchor-consistent information in memory. They might think that the chances will be so high, because sanitary facilities and health care are poor in India, so epidemics are likely. If they have to say whether the probability of that epidemic is lower or higher than 10%, diVerent thoughts will come to mind more easily, e.g., ‘well, they recently overcame an outbreak, so they will be immune and recurrence of this pestilence is unlikely.’ The recency of the anchor-consistent thoughts renders them to be more accessible than other thoughts that are relevant for the absolute judgment. To generate this absolute judgment, judges rely primarily on these easily accessible thoughts (Higgins, 1996) and according to the Selective Accessibility Model, they will
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use these thoughts—if applicable and representative— for the absolute judgment. As a consequence, this judgment is inXuenced by the anchor-consistent knowledge generated before. However, Wilson et al. (1996) demonstrated that there is still an anchor eVect when the thoughts, generated during the comparative judgment, are not applicable or representative for the absolute judgment. In their Wrst experiment, they asked some participants to compare an anchor value to the number of countries in the United Nations and other participants to compare this anchor value to the number of physicians in the Yellow Pages of the local phone book. Next, they all had to estimate the number of local physicians. So, for some participants the target in the comparative and in the absolute judgment was the same, for others the target was diVerent for both judgments. In both conditions, a signiWcant anchor eVect emerged, although the eVect size was smaller in the latter condition. Ergo, to obtain an anchor eVect it is not necessary that the target in both judgments is the same (see also Wong & Kwong (2000), for similar Wndings). If the targets in both judgments do not have to be identical, one may question whether a comparative judgment is a necessity for an anchor eVect to occur. Wilson et al. (1996) demonstrated that a comparative judgment is not necessary. In Experiment 2, they skipped the comparative judgment and introduced the anchor value in a completely diVerent way. Participants received an identiWcation number of which they had, depending on condition, to check diVerent properties. For example, they had to note whether their number was written in red or blue ink. Subsequent estimates assimilated towards these identiWcation numbers (i.e., the anchor values). In Experiment 3 in the same series, Wilson et al. (1996) used still another way to introduce the anchor value. Participants had to copy down a series of anchor values within a certain range (around 4500). After completing this task, they had to make a quantitative estimate (e.g., the number of current students who will get cancer in the near future). Participants who copied down 35 numbers anchored on these numbers, participants who copied down seven numbers did not. A few repetitions was not suYcient, but more worked out. Based on these studies, Wilson et al. (1996) concluded that ‘basic anchoring eVects’ exist and that the only prerequisite for an anchor eVect is a minimal amount of attention paid to the anchor value. The numeric priming account of anchoring Wts the results by Wilson et al. (1996) and Wong and Kwong (2000). In the numeric priming account (e.g., Jacowitz & Kahneman, 1995), it is assumed that the estimation of a quantity or a chance is an automatic process resulting in some weighted combination of all activated numbers. Jacowitz and Kahneman (1995, p. 1162) put it like this:
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“The intuitive estimate of an uncertain quantity is a complex memory task, which involves implicit, automatic, and uncontrolled activation of candidate answers; the Wnal estimate is often a blend or compromise in which any activated answer is assigned some weight (Strack, 1992; Wilson & Brekke, 1994). The anchor aVects the response because it is treated as a candidate answer in this automatic process.” For example, one is Wrst presented with an anchor value (e.g., 90) and next asked to estimate the likelihood of an epidemic of pestilence (expressed as a percentage). Some candidate answers will be activated (e.g., 5%, 20%, and 90%). These candidate answers are based on knowledge that is for whatever reason activated in memory (e.g., 5% and 20% might pop up because a judge has heard of these percentages as chances on comparable diseases). Due to its recent presentation the anchor value, 90, is also accessible and a candidate answer. If we assume that the candidate answers are assigned the same weight and that the combination reXects an average (cf. Lopes, 1985) then the Wnal likelihood estimate is around 38% (i.e., the average of 5, 20, and 90). Had the preceding anchor value in this example been 10, then the likelihood estimate would have been lower, around 12% (i.e., the average of 5, 20, and 10). It has been argued that from a purely numeric priming perspective one would expect the easily accessible anchor value itself to be frequently provided as the absolute estimate (e.g., Mussweiler & Strack, 1999). However, the numeric priming theory of anchoring does not predict this. This theory states that the quantitative estimate reXects some weighted combination of all activated numbers (not only the anchor value). From our example above, it will be clear that it depends on the values of the other candidate answers (retrieved from memory) whether the absolute estimates are wide apart from the anchor value or around or at this value. In this particular example, the candidate answers were equally weighted and “averaged” into the Wnal estimate. The same argument holds for other weighted combinations of candidate answers, in the sense that the numeric priming account of anchoring does not assume that the anchor value itself will be frequently provided as the absolute estimate. We have seen that several elements can be stripped from the standard paradigm without annihilating the anchor eVect (e.g., relevancy of the anchor value, identical targets in the comparative judgment and in the absolute estimate, presence of a comparative judgment). However, there is at least one element left that may be removed from the standard paradigm. In all studies up to now, the anchor value was presented supraliminally. The question is whether there is also an anchor eVect when the anchor value is presented subliminally, i.e., when the anchor value is presented too short to be aware of its presentation.
Quite a lot of phenomena that were Wrst demonstrated with supraliminal activation techniques are later replicated with the use of subliminal presentation techniques (for a review, see Dijksterhuis, Aarts, & Smith, 2003): Higgins, Rholes, and Jones (1977) showed that supraliminal exposure to trait terms inXuenced impressions we form of others. Bargh and Pietromonaco (1982) demonstrated that this eVect could be evoked by subliminal activation of a trait construct as well. Fazio, Sanbonmatsu, Powell, and Kardes (1986) demonstrated that supraliminal words were automatically evaluated. Greenwald, Klinger, and Liu (1989) and Greenwald, Klinger, and Schuh (1995) obtained evidence for the automatic evaluation of subliminally presented stimuli. In light of these Wndings, subliminal priming seems a phenomenon that may occur across a variety of domains. Relevant to this issue, the eVect of subliminally presented numerical primes has been demonstrated by Dehaene et al. (1998) and by Naccache and Dehaene (2001). In their study, they presented their participants with a number between 1 and 9. Participants had to judge whether this number was higher or lower than 5. However, just before this number was presented, another number (also between 1 and 9), the prime, was presented for a very short duration (43 ms), so the participants were not able to consciously perceive this number. In some trials, the prime was congruent with the target (both numbers fell on the same side of 5) and in other trials they were incongruent. The response latencies and measured brain activity indicate that the subliminal prime had been ‘perceived’ and processed. Thus, Dehaene et al. demonstrated an eVect of subliminally presented numbers on higher/lower judgments (not on absolute numerical estimates). Based on the numeric priming account of anchoring which states that the anchor eVect is caused by the heightened activation level of merely the number (i.e., the anchor value) and generalizing from subliminal priming studies in other domains, we expect a subliminally presented anchor value to inXuence a subsequent quantitative estimate. The anchor eVect in the standard paradigm is characterized by temporal robustness (Mussweiler, 2001). Mussweiler and Strack (2001b) found that anchor eVects due to numeric priming are fairly transitive and short-lived. Since the subliminal anchor eVect will be open to numeric priming processes, we expect this eVect to be short-lived. This expectation is also based on subliminal priming studies in which it has frequently been demonstrated that the duration of the eVects of subliminally primes is restricted presumably because the activation level of the prime decreases over time (e.g., Forster & Davis, 1984). One way to shorten the lag between the subliminal prime and the target is to instruct participants to give their answer quickly. Besides a shorter lag, time pressure brings
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about other things. In another domain of psychological research it has been demonstrated that time pressure prevents long elaborations and these elaborations might diminish the inXuence of the prime (Schwarz, Strack, Hippler, & Bishop, 1991). Furthermore, time pressure interferes with extensive recall processes and increases reliance on the Wrst thing that comes to mind (see Kruglanski, 1980) and induces to resort to heuristic processing strategies (Kahneman, Slovic, & Tversky, 1982) at the expense of detail-oriented piecemeal processing strategies (e.g., Strack, Erber, & Wicklund, 1982). Time pressure heightens the need for closure (Kruglanski & Webster, 1996), which in turn leads to less elaborate processing, thus, they consider less evidence before forming a judgment (cf. Mayseless & Kruglanski, 1987; see also Strack et al., 1982). If numeric priming is the underlying process of anchoring then the reasons to expect an anchor eVect especially under time pressure could be the following. In the numeric priming account of anchoring, it is assumed that the Wnal quantitative estimate reXects some weighted combination of all activated candidate answers. The generation of (a lot of) candidate answers needs time: the Wrst one or two may immediately come to mind but next one has to retrieve from memory what one knows about the target stimulus, and what the implications of this knowledge might be and these retrieval and thought processes are probably time consuming (cf. “ease of retrieval” studies e.g., Schwarz, Bless et al., 1991; Winkielman, Schwarz, & Belli, 1998). When asked to give their quantitative estimate quickly, people will generate less candidate answers compared to conditions without such time pressure. Thus, fewer alternative numbers are available to be combined with the anchor value into the Wnal quantitative estimate. Provided that the anchor value diVers from the alternative candidate answers, it will have more inXuence on this weighted combination if there are only a few candidate answers (e.g., two instead of four). Consequently, everything else being equal, the impact of the anchor value on the quantitative estimate will be larger under time pressure. In sum, based on the numeric priming account of anchoring and generalizing from subliminal priming studies in other domains we expect a subliminally presented anchor value to inXuence a subsequent quantitative estimate, provided that the time lag is short. In our experiment, we repeatedly present a high or a low subliminal anchor value.1 Next, we ask participants
1 In this study, we are interested in the mere existence of subliminal anchoring. The existence of such anchoring becomes apparent if the estimates are higher in the high anchor condition than in the low anchor condition. If one is interested in speciWc properties of the anchor eVect (e.g., stronger assimilation towards the high than the low anchor or vice versa), one might apply the calibration procedure with unanchored estimates designed for this purpose by Jacowitz and Kahneman (1995).
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to estimate the probability of recurrence of an epidemic of pestilence of the lungs in India within a year. Half of the participants are pressed to give their answer quickly, the other half is not under time pressure. Our expectation is that in the low Anchor condition participants will estimate these chances lower than in the high Anchor condition, but only if they are under Time Pressure.
Method Participants and design Sixty-two students of Leiden University participated in this experiment (82% female). They were randomly assigned to one of the cells of a 2 (Anchor: low, high) £ 2 (Time Pressure: absent, present) between participants factorial design. The main dependent variable was the estimate of the probability of recurrence of an epidemic of pestilence of the lungs in India within a year. This probability was expressed as a percentage. Procedure Participants were invited to the laboratory, where they were placed in separate cubicles, each containing a computer, which was used to present the information and to register the dependent measures. Obviously, all numbers in the laboratory, like room numbers, serial numbers on the computer, etceteras, were hidden to avoid any possible inXuence on participants’ estimates. Participants were told that the experiment was about how people make estimates. First, they had to estimate if there was predominance of capital or lower case letters in several letter combinations. After that, they had to make some probability estimates. The letter combination task was used to present the anchor value subliminally. In this task, participants had to estimate if a letter combination of six letters (e.g., MJFqRe) contained more capital letters or more lower case letters. In the instruction it was stated that we knew from experience that participants were able to give the correct answer, when they followed their Wrst impression. They were familiarized with this task by an exercise. After this exercise, the series of letter combinations were presented. These series had been carefully composed. First of all, there were as many capital letters as lower case letters added over the letter combinations. This was done to prevent participants to deduce any cues from the letter combinations for the probability estimate. Second, letters with a chance of confusion were avoided (e.g., c/C, k/K, and v/V). MacIntosh Performa 5320 computers were used to present the stimuli. The letter combinations were presented in this way: Wrst, two crosses appeared during
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0.5 s, immediately followed by the anchor value. The aim of the crosses was to focus participants’ attention upon the place of the screen where the anchor value appeared, namely on the same spot as the crosses. The time during which the anchor value was presented was 17 ms. A mask (again two crosses that appeared for 17 ms) immediately erased the anchor value. Immediately after the mask, the letter combination was presented during 1.5 s. So this letter combination also functioned as a mask. All characters on the screen, including the anchor value, were presented in a Chigaco font, plain, size 14 pt., 4.5 mm high. The viewing distance was about 0.5 m. In each of the 15 letter combinations the anchor value was presented. In the high Anchor condition, this number was ‘10,’ in the low Anchor condition, this number was ‘90.’2 After the last letter combination, a screen was presented for 5 s with the announcement that this was the last letter combination and that they had to make the probability estimate. For the participants in the conditions with Time Pressure the probability estimate was preceded by the instruction: “please, give your answer quickly.” For the participants in the conditions without Time Pressure this instruction was omitted. Immediately after the presentation of this screen, participants had to estimate the probability of recurrence of an epidemic of pestilence of the lungs in India within a year.
Results
the participants. The conclusion is that participants were concentrated while working on this task in which the anchor value was presented subliminally. A 2 (Anchor: low, high) £ 2 (Time Pressure: absent, present) ANOVA with as dependent variable the total number of errors made in the letter combination task revealed no eVects of the experimental factors, Fs (1, 58) < 1, ns. Time Pressure The eVect of the factor Time Pressure was examined by analyzing the response latency between the last subliminal presentation of the anchor value and the probability estimate of an epidemic. A 2 (Anchor: low, high) £ 2 (Time Pressure: absent, present) ANOVA revealed a signiWcant main eVect of Time Pressure, F (1, 58) D 8.56, p < .01. Under Time Pressure, the response latency between the last subliminally presented anchor value and the probability estimate was signiWcantly shorter (M D 22.20 s) than when there is no Time Pressure (M D 28.28 s). There were no other main or interaction eVects, Fs (1, 58) < 1, ns. It is important to note that a part of this response latency was Wxed: The screen with the announcement of the probability estimate appeared for 5 s in all conditions. Moreover, in all conditions part of this response latency was used for reading the quite long question. Thus, the relative diVerence in actual response times between the conditions with and without Time Pressure might be larger than reXected by the reported means.
Manipulation checks Main dependent variable Letter combinations In general, participants did well on the letter combination task. On average each letter combination had been judged accurately (i.e., accurate identiWcation of predominance of capital or lower case letters) by 89% of 2 As a pilot study (N D 30) we conducted an awareness check (see Bargh & Chartrand, 2000) to check that participants did not consciously perceive the subliminally presented anchor value. In this awareness check, the anchor value (10 or 90, dependent on condition) is presented 15 times for 17 ms, preceded and followed by two crosses, like in the letter combinations. Participants were informed that between the crosses nothing, a word, a number or a picture was presented and participants were asked what they saw. This was repeated a second time. The third time, we again presented the anchor value for 15 times, and asked whether they saw nothing, the number 10, 30, 50, 70 or 90. Thus, the correct answers for question 1, 2, and 3, respectively, were a number, a number, and 10 or 90 (dependent on condition). In total 97.7% of the participants made one or more errors. More than half of the participants (56.7%) answered none of the three questions correctly. Another 36.7% gave only one correct answer. There was one participant (3.3%) who had two correct answers and there was only one (3.3%) who had all three answers correct. There is no diVerence in the number of correct answers between the low (M D .40) and the high Anchor condition (M D .67), F (1, 28) D 1.00, ns. So, it is safe to conclude that participants were not able to consciously perceive the subliminally presented anchor value.
We expected that in the conditions with Time Pressure, the subliminally presented anchor value would inXuence the probability estimate. Inspection of the means in Table 1 reveals that the expected pattern was obtained. A 2 (Anchor: low, high) £ 2 (Time Pressure: absent, present) ANOVA revealed a signiWcant interaction eVect between Anchor and Time Pressure, F (1, 58) D 5.06, p < .05. In the conditions with Time Pressure, participants estimate the probability of an epidemic higher in the high Anchor condition (M D 39.40) than in the low Anchor condition (M D 20.00). There were no signiWcant main eVects,
Table 1 Means (standard deviation) of the probability estimates as a function of Anchor and Time Pressure Anchor
Low High
Time Pressure Present
Absent
20.00 (19.89) 39.40 (24.63)
32.06 (24.44) 25.56 (21.23)
Note. Probability estimates are expressed in percentages. n D 15 or 16 per cell.
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Fs (1, 58) < 1, ns. Thus, the anchor eVect critically depended on whether there was Time Pressure or not. The diVerence between the high and the low Anchor condition was only signiWcant for the conditions in which there was Time Pressure, t(28) D 2.37, p < .05 and not for the conditions in which there was no Time Pressure, t(30) < 1, ns. (high Anchor condition, M D 25.56, low Anchor condition M D 32.06). This conWrms our expectations.
Discussion The results of our study indicate that there is a subliminal anchor eVect and that this eVect is short-lived. The probability estimate assimilated towards the subliminally presented anchor value in the conditions with time pressure. In the Introduction section, we described two reasons to expect an anchor eVect only in the conditions with time pressure. One reason is that in the conditions with time pressure, the time between the last subliminal presentation of the anchor value and the absolute estimate is shorter than in the conditions without time pressure. Because the accessibility level of the subliminally presented anchor value will decrease with time, the chances that the anchor value will still be activated is higher in the conditions with time pressure than in the conditions without time pressure. The second reason is that time pressure interferes with extensive recall processes and increases reliance on the Wrst thing that comes to mind. Participants will generate less candidate answers under time pressure. Thus, fewer alternative numbers are available to be combined with the anchor value into the Wnal quantitative estimate. Provided that the anchor value diVers from the alternative candidate answers, it will have more inXuence on the weighted combination of candidate answers if there are only a few (e.g., two instead of four). Consequently, the impact of the anchor value on the quantitative estimate will be larger under time pressure. One or both of these processes (less decay of the anchor’s activation level or less systematic judgment resulting in less candidate answers and relatively more impact of the anchor value) may have played a role. One way to Wnd out to what extent these processes played a role is to do a study in which two time delays are systematically manipulated (i.e., the time between the last subliminal presentation of the anchor and the presentation of the question for the absolute estimate, and the time allowed to the participants to answer this question) and also the (im)possibility to generate candidate answers. Research using the standard paradigm of anchor research, that is a combination of a comparative and a subsequent absolute judgment, has provided numerous demonstrations of strong and durable anchor eVects.
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However, not all elements of the standard paradigm are needed for an anchor eVect. There is, for instance, still an eVect when the anchor value is blatantly irrelevant for the quantitative estimate, and when the target in the comparative and the absolute judgment are not the same. Even when there is no comparative judgment and the anchor value is brieXy introduced in some superWcial way (e.g., participants have to check the color of the number), an anchor eVect emerges. However, it seems that the size and the durability of the anchor eVect decreases when elements of the standard paradigm are stripped. Our study showed that one of the Wnal elements of the standard paradigm, i.e., supraliminal presentation of the anchor value, is no prerequisite for the occurrence of the anchor eVect. This subliminal anchor eVect appears to be even more basic than the “basic anchoring” eVect found by Wilson et al. (1996). The prerequisite for Wilson et al.’s basic anchoring was a minimal amount of attention paid to the anchor value. In our experiment we demonstrated that even when participants could not pay attention to the subliminally presented anchor value, an anchor eVect still emerged. We are certain that participants could not attend to the anchor values because the presentation time (17 ms) is according to Bargh and Chartrand (2000) adequately short for stimuli, presented in the foveal visual Weld, to be truly subliminal. We think that a likely explanatory mechanism of the subliminal anchor eVect is the numeric priming account: the accessibility level of the subliminally presented anchor value (i.e., merely the number itself and not semantically related thoughts) is heightened and this leads to activation of the anchor value as a candidate answer to the probability estimate, so that this judgment assimilates towards this anchor value. Several studies have been done in which it has been suggested that anchor eVects may be caused by numeric priming (Brewer & Chapman, 2002; Jacowitz & Kahneman, 1995; Wilson et al., 1996; Wong & Kwong, 2000). Mussweiler and Strack (2001b) also report anchoring eVects due to numeric priming processes when semantic processes are incapacitated. In our study, the anchor value is presented subliminally. This is a condition atypical of the standard paradigm of anchoring. Under this condition, it is highly unlikely that participants have generated semantically related information by the subliminally presented anchor value as in the Selective Accessibility Model. While semantic priming processes cannot play a role, numeric priming processes can. Mussweiler and Strack (2001b) stated that the numeric priming processes of anchoring implies that the anchor eVect is fairly transitive and short-lived. Indeed, we found the subliminal anchor eVect to be short-lived. As far as we know, the present research is the Wrst demonstration of a subliminal anchor eVect. We think
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that the demonstration of this eVect contributes to the present discussion in the Weld of anchoring about the conditions under which an anchor eVect occurs. For decades, most research on the anchor eVect used the standard paradigm. More recently, it has been shown that anchoring also exists under conditions diVerent from the standard paradigm. Wilson et al. (1996) demonstrated the existence of basic anchoring eVects. Until recently, this was the only demonstration of the basic anchoring eVect. Brewer and Chapman (2002) performed a series of studies and replicated this eVect, although they also showed limited generality of basic anchoring. Our demonstration of a subliminal anchor eVect, where nearly all elements of the standard paradigm have been stripped, supports the existence of anchor eVects that are even more basic than previously thought. Even if a number is merely Xashed on a screen and judges are unaware of this number, their subsequent probability estimate assimilates towards this number. Although this eVect is short-lived, it is proof of the pervasive nature of anchoring. If conditions are favorable anchor eVects may dominate quantitative estimates, but even if conditions are harsh anchor eVects may still emerge. References Bargh, J. A., & Chartrand, T. L. (2000). The mind in the middle: A practical guide to priming and automaticity research. In H. T. Reis & C. M. Judd (Eds.), Handbook of research methods in social and personality psychology (pp. 253–285). New York: Cambridge University Press. Bargh, J. A., & Pietromonaco, P. (1982). Automatic information processing and social perception: The inXuence of trait information presented outside of conscious awareness on impression formation. Journal of Personality and Social Psychology, 43, 437–449. Brewer, N. T., & Chapman, G. B. (2002). The fragile basic anchoring eVect. Journal of Behavioral Decision Making, 15, 65–77. Chapman, G. B., & Bornstein, B. H. (1996). The more you ask for, the more you get: Anchoring in personal injury verdicts. Applied Cognitive Psychology, 10, 519–540. Chapman, G. B., & Johnson, E. J. (1999). Anchoring, activation and the construction of values. Organizational Behavior and Human Decision Processes, 79, 115–153. Daamen, D., de Vries, I., & Kesnich, E. (1996). Hoe robuust is het ankering- en- aanpassingseVect? Kansen op rampen in woorden en getallen en de rol van ongeloofwaardige ankerinformatie. [On the robustness of anchoring-and-adjustment. Verbal versus numerical probabilities of disasters and non-credible anchor information.] In E. van Schie et al. (Eds.), Sociale Psychologie en haar toepassingen (Reeks toegepaste sociale psychologie, deel X). Delft: Eburon. Dehaene, S., Naccache, L., Le Clec’H, G., Koechlin, E., Mueller, M., Dehaene-Lambertz, G., et al.(1998). Imaging unconscious semantic priming. Nature, 395, 597–600. Dijksterhuis, A., Aarts, H., & Smith, P. K. (2003). The power of the subliminal: On subliminal persuasion and other potential applications. In R. Hassin, J. S. Uleman, & J. A. Bargh (Eds.), Unintended thought 2: The new unconscious. New York: Oxford University Press. Englich, B., & Mussweiler, T. (2001). Sentencing under uncertainty: Anchoring eVects in the courtroom. Journal of Applied Social Psychology, 31, 1535–1551.
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M. Reitsma-van Rooijen, D.D. L. Daamen / Journal of Experimental Social Psychology 42 (2006) 380–387 Schwarz, N., Strack, F., Hippler, H. J., & Bishop, G. (1991). The impact of administration mode on response eVects in survey measurement. Applied Cognitive Psychology, 5, 193–212. Smith, J. F., & Kida, T. (1991). Heuristics and biases: Expertise and task realism in auditing. Psychological Bulletin, 109, 472–489. Strack, F., Erber, R., & Wicklund, R. (1982). EVects of salience and time pressure on ratings of social causality. Journal of Experimental Social Psychology, 18, 581–594. Strack, F., & Mussweiler, T. (1997). Explaining the enigmatic anchoring eVect: Mechanisms of selective accessibility. Journal of Personality and Social Psychology, 73, 437–446.
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Tversky, A., & Kahneman, D. (1974). Judgment under uncertainty: Heuristics and biases. Science, 185, 1124–1131. Wilson, T. D., Houston, C., Etling, K. M., & Brekke, N. (1996). A new look at anchoring eVects: Basic anchoring and its antecedents. Journal of Experimental Psychology: General, 125, 387–402. Winkielman, P., Schwarz, N., & Belli, R. F. (1998). The role of ease of retrieval and attribution in memory judgments: Judging your memory as worse despite recalling more events. Psychological Science, 9, 124–126. Wong, K. F. E., & Kwong, J. Y. (2000). Is 7300 m equal to 7.3 km? Same semantics but diVerent anchoring eVects. Organizational Behavior and Human Decision Processes, 82, 314–333.
Subliminal anchoring: The eVects of subliminally presented numbers on probability estimates 夽 Margreet Reitsma-van Rooijen a,¤, Dancker D. L. Daamen b a
Department of Social Psychology, Vrije Universiteit Amsterdam, van der Boechorststraat 1, 1081 BT Amsterdam, The Netherlands b Department of Social and Organizational Psychology, Leiden University, The Netherlands Received 13 August 2004; revised 28 April 2005 Available online 20 July 2005
Abstract Previous research demonstrated that if attention is paid to a supraliminally presented number, a subsequent quantitative estimate assimilates towards this number (the anchor eVect). One explanation states that this eVect is merely caused by the heightened accessibility level of the anchor value itself. Based on this numeric priming account and generalizing from subliminal priming studies, we expected a short-lived subliminal anchor eVect. We presented participants subliminally with a low or high anchor value (10 or 90) and next they had to estimate the probability of an epidemic. Half of them were pressed to do this quickly. Only under time pressure, a signiWcant anchor eVect emerged. © 2005 Elsevier Inc. All rights reserved. Keywords: Anchoring; Subliminal; Numeric priming
Numerical anchoring is the assimilation of a quantitative estimate towards a previously presented number. In one of the Wrst research demonstrations of this eVect, Tversky and Kahneman (1974) asked people to estimate the percentage of African countries in the United Nations. In one condition they were Wrst asked whether this percentage was higher or lower than 10%. In another condition 10% was replaced by 65%. The estimate of the percentage of African countries assimilated towards the percentage in the Wrst question: in the Wrst condition the median estimate was 25%, in the latter condition it was 45%. This anchor eVect has often been demonstrated in a broad range of quantitative judgments such as general knowledge (Chapman & Johnson, 1999; Jacowitz & Kahneman, 1995; Tversky & Kahneman, 1974; Wilson, 夽 We thank Ap Dijksterhuis for valuable advice, and Henk Aarts and Sander Koole for helpful comments on an earlier draft of this article. * Corresponding author. Fax: +31 (0) 20 5988921. E-mail address: [email protected] (M. Reitsma-van Rooijen).
0022-1031/$ - see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jesp.2005.05.001
Houston, Etling, & Brekke, 1996), probability estimates (Plous, 1989), legal judgment (e.g., Chapman & Bornstein, 1996), pricing decisions (Northcraft & Neale, 1987), and negotiation (Ritov, 1996) (for a recent review, see Mussweiler & Strack, 1999). Anchoring is a strong and robust eVect. Not only laymen are susceptible to anchor eVects but also experts when they give judgments in their Weld of expertise, e.g., accountants (Smith & Kida, 1991), real estate agents (Northcraft & Neale, 1987), and judges (Englich & Mussweiler, 2001). Furthermore, the anchor eVect is diYcult to avoid, even when people are forewarned (Wilson et al., 1996). In most demonstrations of the anchor eVect, the anchoring process is initiated by explicitly asking people to compare a supraliminally presented anchor value to a target. They have, for example, to judge whether the chances of recurrence of an epidemic of pestilence of the lungs in India within a year are lower or higher than 10%. After this comparative judgment, they have to make an absolute judgment in which these chances must be estimated exactly (Daamen, de Vries, & Kesnich, 1996). The
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sequence of a comparative and an absolute judgment has become the dominant paradigm (or as termed by Strack & Mussweiler, 1997, the “standard paradigm”) of anchor research. As a consequence, most of the explanations of the anchor eVect have focused on the role of the comparative judgment in the anchor process in that paradigm. Other ways to introduce the anchor value, which diVer from the standard paradigm, have received relatively little attention. The question is whether this standard paradigm is the only way to obtain an anchor eVect. The standard paradigm consists of a number of elements: an anchor value, which can be perceived as either relevant or irrelevant, a comparative judgment in which the anchor value is presented supraliminally, an absolute judgment and in both judgments a target, which can either be the same or diVerent in both judgments. Maybe not all these elements are needed to obtain an anchor eVect. There are many research examples of strong anchor eVects given a relevant anchor value (e.g., Northcraft & Neale, 1987). However, there is still an anchor eVect if the anchor value is clearly irrelevant, for example, if the anchor value is obviously random, for example, when the anchor value resulted from the spin of a ‘wheel of fortune’ (Tversky & Kahneman, 1974; see also Russo and Shoemaker, 1989, as cited in Chapman & Johnson, 1999) or highly implausible (Mussweiler & Strack, 2001a). Taken together, it appears that both relevant and irrelevant anchor values produce anchor eVects. To account for these anchor eVects, the Selective Accessibility Model (e.g., Strack & Mussweiler, 1997; Mussweiler & Strack, 1999) has been proposed. A fundamental assumption in this model is that one compares the target of the absolute judgment to the anchor value by applying a hypothesis-consistent strategy. As a result the accessibility of anchor-consistent information in memory is heightened. This activation of semantically related information is a crucial part of the Selective Accessibility Model. For example, when it is asked whether the chances for recurrence of the epidemic of pestilence of the lungs are lower or higher than 90%, participants will search for anchor-consistent information in memory. They might think that the chances will be so high, because sanitary facilities and health care are poor in India, so epidemics are likely. If they have to say whether the probability of that epidemic is lower or higher than 10%, diVerent thoughts will come to mind more easily, e.g., ‘well, they recently overcame an outbreak, so they will be immune and recurrence of this pestilence is unlikely.’ The recency of the anchor-consistent thoughts renders them to be more accessible than other thoughts that are relevant for the absolute judgment. To generate this absolute judgment, judges rely primarily on these easily accessible thoughts (Higgins, 1996) and according to the Selective Accessibility Model, they will
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use these thoughts—if applicable and representative— for the absolute judgment. As a consequence, this judgment is inXuenced by the anchor-consistent knowledge generated before. However, Wilson et al. (1996) demonstrated that there is still an anchor eVect when the thoughts, generated during the comparative judgment, are not applicable or representative for the absolute judgment. In their Wrst experiment, they asked some participants to compare an anchor value to the number of countries in the United Nations and other participants to compare this anchor value to the number of physicians in the Yellow Pages of the local phone book. Next, they all had to estimate the number of local physicians. So, for some participants the target in the comparative and in the absolute judgment was the same, for others the target was diVerent for both judgments. In both conditions, a signiWcant anchor eVect emerged, although the eVect size was smaller in the latter condition. Ergo, to obtain an anchor eVect it is not necessary that the target in both judgments is the same (see also Wong & Kwong (2000), for similar Wndings). If the targets in both judgments do not have to be identical, one may question whether a comparative judgment is a necessity for an anchor eVect to occur. Wilson et al. (1996) demonstrated that a comparative judgment is not necessary. In Experiment 2, they skipped the comparative judgment and introduced the anchor value in a completely diVerent way. Participants received an identiWcation number of which they had, depending on condition, to check diVerent properties. For example, they had to note whether their number was written in red or blue ink. Subsequent estimates assimilated towards these identiWcation numbers (i.e., the anchor values). In Experiment 3 in the same series, Wilson et al. (1996) used still another way to introduce the anchor value. Participants had to copy down a series of anchor values within a certain range (around 4500). After completing this task, they had to make a quantitative estimate (e.g., the number of current students who will get cancer in the near future). Participants who copied down 35 numbers anchored on these numbers, participants who copied down seven numbers did not. A few repetitions was not suYcient, but more worked out. Based on these studies, Wilson et al. (1996) concluded that ‘basic anchoring eVects’ exist and that the only prerequisite for an anchor eVect is a minimal amount of attention paid to the anchor value. The numeric priming account of anchoring Wts the results by Wilson et al. (1996) and Wong and Kwong (2000). In the numeric priming account (e.g., Jacowitz & Kahneman, 1995), it is assumed that the estimation of a quantity or a chance is an automatic process resulting in some weighted combination of all activated numbers. Jacowitz and Kahneman (1995, p. 1162) put it like this:
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“The intuitive estimate of an uncertain quantity is a complex memory task, which involves implicit, automatic, and uncontrolled activation of candidate answers; the Wnal estimate is often a blend or compromise in which any activated answer is assigned some weight (Strack, 1992; Wilson & Brekke, 1994). The anchor aVects the response because it is treated as a candidate answer in this automatic process.” For example, one is Wrst presented with an anchor value (e.g., 90) and next asked to estimate the likelihood of an epidemic of pestilence (expressed as a percentage). Some candidate answers will be activated (e.g., 5%, 20%, and 90%). These candidate answers are based on knowledge that is for whatever reason activated in memory (e.g., 5% and 20% might pop up because a judge has heard of these percentages as chances on comparable diseases). Due to its recent presentation the anchor value, 90, is also accessible and a candidate answer. If we assume that the candidate answers are assigned the same weight and that the combination reXects an average (cf. Lopes, 1985) then the Wnal likelihood estimate is around 38% (i.e., the average of 5, 20, and 90). Had the preceding anchor value in this example been 10, then the likelihood estimate would have been lower, around 12% (i.e., the average of 5, 20, and 10). It has been argued that from a purely numeric priming perspective one would expect the easily accessible anchor value itself to be frequently provided as the absolute estimate (e.g., Mussweiler & Strack, 1999). However, the numeric priming theory of anchoring does not predict this. This theory states that the quantitative estimate reXects some weighted combination of all activated numbers (not only the anchor value). From our example above, it will be clear that it depends on the values of the other candidate answers (retrieved from memory) whether the absolute estimates are wide apart from the anchor value or around or at this value. In this particular example, the candidate answers were equally weighted and “averaged” into the Wnal estimate. The same argument holds for other weighted combinations of candidate answers, in the sense that the numeric priming account of anchoring does not assume that the anchor value itself will be frequently provided as the absolute estimate. We have seen that several elements can be stripped from the standard paradigm without annihilating the anchor eVect (e.g., relevancy of the anchor value, identical targets in the comparative judgment and in the absolute estimate, presence of a comparative judgment). However, there is at least one element left that may be removed from the standard paradigm. In all studies up to now, the anchor value was presented supraliminally. The question is whether there is also an anchor eVect when the anchor value is presented subliminally, i.e., when the anchor value is presented too short to be aware of its presentation.
Quite a lot of phenomena that were Wrst demonstrated with supraliminal activation techniques are later replicated with the use of subliminal presentation techniques (for a review, see Dijksterhuis, Aarts, & Smith, 2003): Higgins, Rholes, and Jones (1977) showed that supraliminal exposure to trait terms inXuenced impressions we form of others. Bargh and Pietromonaco (1982) demonstrated that this eVect could be evoked by subliminal activation of a trait construct as well. Fazio, Sanbonmatsu, Powell, and Kardes (1986) demonstrated that supraliminal words were automatically evaluated. Greenwald, Klinger, and Liu (1989) and Greenwald, Klinger, and Schuh (1995) obtained evidence for the automatic evaluation of subliminally presented stimuli. In light of these Wndings, subliminal priming seems a phenomenon that may occur across a variety of domains. Relevant to this issue, the eVect of subliminally presented numerical primes has been demonstrated by Dehaene et al. (1998) and by Naccache and Dehaene (2001). In their study, they presented their participants with a number between 1 and 9. Participants had to judge whether this number was higher or lower than 5. However, just before this number was presented, another number (also between 1 and 9), the prime, was presented for a very short duration (43 ms), so the participants were not able to consciously perceive this number. In some trials, the prime was congruent with the target (both numbers fell on the same side of 5) and in other trials they were incongruent. The response latencies and measured brain activity indicate that the subliminal prime had been ‘perceived’ and processed. Thus, Dehaene et al. demonstrated an eVect of subliminally presented numbers on higher/lower judgments (not on absolute numerical estimates). Based on the numeric priming account of anchoring which states that the anchor eVect is caused by the heightened activation level of merely the number (i.e., the anchor value) and generalizing from subliminal priming studies in other domains, we expect a subliminally presented anchor value to inXuence a subsequent quantitative estimate. The anchor eVect in the standard paradigm is characterized by temporal robustness (Mussweiler, 2001). Mussweiler and Strack (2001b) found that anchor eVects due to numeric priming are fairly transitive and short-lived. Since the subliminal anchor eVect will be open to numeric priming processes, we expect this eVect to be short-lived. This expectation is also based on subliminal priming studies in which it has frequently been demonstrated that the duration of the eVects of subliminally primes is restricted presumably because the activation level of the prime decreases over time (e.g., Forster & Davis, 1984). One way to shorten the lag between the subliminal prime and the target is to instruct participants to give their answer quickly. Besides a shorter lag, time pressure brings
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about other things. In another domain of psychological research it has been demonstrated that time pressure prevents long elaborations and these elaborations might diminish the inXuence of the prime (Schwarz, Strack, Hippler, & Bishop, 1991). Furthermore, time pressure interferes with extensive recall processes and increases reliance on the Wrst thing that comes to mind (see Kruglanski, 1980) and induces to resort to heuristic processing strategies (Kahneman, Slovic, & Tversky, 1982) at the expense of detail-oriented piecemeal processing strategies (e.g., Strack, Erber, & Wicklund, 1982). Time pressure heightens the need for closure (Kruglanski & Webster, 1996), which in turn leads to less elaborate processing, thus, they consider less evidence before forming a judgment (cf. Mayseless & Kruglanski, 1987; see also Strack et al., 1982). If numeric priming is the underlying process of anchoring then the reasons to expect an anchor eVect especially under time pressure could be the following. In the numeric priming account of anchoring, it is assumed that the Wnal quantitative estimate reXects some weighted combination of all activated candidate answers. The generation of (a lot of) candidate answers needs time: the Wrst one or two may immediately come to mind but next one has to retrieve from memory what one knows about the target stimulus, and what the implications of this knowledge might be and these retrieval and thought processes are probably time consuming (cf. “ease of retrieval” studies e.g., Schwarz, Bless et al., 1991; Winkielman, Schwarz, & Belli, 1998). When asked to give their quantitative estimate quickly, people will generate less candidate answers compared to conditions without such time pressure. Thus, fewer alternative numbers are available to be combined with the anchor value into the Wnal quantitative estimate. Provided that the anchor value diVers from the alternative candidate answers, it will have more inXuence on this weighted combination if there are only a few candidate answers (e.g., two instead of four). Consequently, everything else being equal, the impact of the anchor value on the quantitative estimate will be larger under time pressure. In sum, based on the numeric priming account of anchoring and generalizing from subliminal priming studies in other domains we expect a subliminally presented anchor value to inXuence a subsequent quantitative estimate, provided that the time lag is short. In our experiment, we repeatedly present a high or a low subliminal anchor value.1 Next, we ask participants
1 In this study, we are interested in the mere existence of subliminal anchoring. The existence of such anchoring becomes apparent if the estimates are higher in the high anchor condition than in the low anchor condition. If one is interested in speciWc properties of the anchor eVect (e.g., stronger assimilation towards the high than the low anchor or vice versa), one might apply the calibration procedure with unanchored estimates designed for this purpose by Jacowitz and Kahneman (1995).
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to estimate the probability of recurrence of an epidemic of pestilence of the lungs in India within a year. Half of the participants are pressed to give their answer quickly, the other half is not under time pressure. Our expectation is that in the low Anchor condition participants will estimate these chances lower than in the high Anchor condition, but only if they are under Time Pressure.
Method Participants and design Sixty-two students of Leiden University participated in this experiment (82% female). They were randomly assigned to one of the cells of a 2 (Anchor: low, high) £ 2 (Time Pressure: absent, present) between participants factorial design. The main dependent variable was the estimate of the probability of recurrence of an epidemic of pestilence of the lungs in India within a year. This probability was expressed as a percentage. Procedure Participants were invited to the laboratory, where they were placed in separate cubicles, each containing a computer, which was used to present the information and to register the dependent measures. Obviously, all numbers in the laboratory, like room numbers, serial numbers on the computer, etceteras, were hidden to avoid any possible inXuence on participants’ estimates. Participants were told that the experiment was about how people make estimates. First, they had to estimate if there was predominance of capital or lower case letters in several letter combinations. After that, they had to make some probability estimates. The letter combination task was used to present the anchor value subliminally. In this task, participants had to estimate if a letter combination of six letters (e.g., MJFqRe) contained more capital letters or more lower case letters. In the instruction it was stated that we knew from experience that participants were able to give the correct answer, when they followed their Wrst impression. They were familiarized with this task by an exercise. After this exercise, the series of letter combinations were presented. These series had been carefully composed. First of all, there were as many capital letters as lower case letters added over the letter combinations. This was done to prevent participants to deduce any cues from the letter combinations for the probability estimate. Second, letters with a chance of confusion were avoided (e.g., c/C, k/K, and v/V). MacIntosh Performa 5320 computers were used to present the stimuli. The letter combinations were presented in this way: Wrst, two crosses appeared during
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0.5 s, immediately followed by the anchor value. The aim of the crosses was to focus participants’ attention upon the place of the screen where the anchor value appeared, namely on the same spot as the crosses. The time during which the anchor value was presented was 17 ms. A mask (again two crosses that appeared for 17 ms) immediately erased the anchor value. Immediately after the mask, the letter combination was presented during 1.5 s. So this letter combination also functioned as a mask. All characters on the screen, including the anchor value, were presented in a Chigaco font, plain, size 14 pt., 4.5 mm high. The viewing distance was about 0.5 m. In each of the 15 letter combinations the anchor value was presented. In the high Anchor condition, this number was ‘10,’ in the low Anchor condition, this number was ‘90.’2 After the last letter combination, a screen was presented for 5 s with the announcement that this was the last letter combination and that they had to make the probability estimate. For the participants in the conditions with Time Pressure the probability estimate was preceded by the instruction: “please, give your answer quickly.” For the participants in the conditions without Time Pressure this instruction was omitted. Immediately after the presentation of this screen, participants had to estimate the probability of recurrence of an epidemic of pestilence of the lungs in India within a year.
Results
the participants. The conclusion is that participants were concentrated while working on this task in which the anchor value was presented subliminally. A 2 (Anchor: low, high) £ 2 (Time Pressure: absent, present) ANOVA with as dependent variable the total number of errors made in the letter combination task revealed no eVects of the experimental factors, Fs (1, 58) < 1, ns. Time Pressure The eVect of the factor Time Pressure was examined by analyzing the response latency between the last subliminal presentation of the anchor value and the probability estimate of an epidemic. A 2 (Anchor: low, high) £ 2 (Time Pressure: absent, present) ANOVA revealed a signiWcant main eVect of Time Pressure, F (1, 58) D 8.56, p < .01. Under Time Pressure, the response latency between the last subliminally presented anchor value and the probability estimate was signiWcantly shorter (M D 22.20 s) than when there is no Time Pressure (M D 28.28 s). There were no other main or interaction eVects, Fs (1, 58) < 1, ns. It is important to note that a part of this response latency was Wxed: The screen with the announcement of the probability estimate appeared for 5 s in all conditions. Moreover, in all conditions part of this response latency was used for reading the quite long question. Thus, the relative diVerence in actual response times between the conditions with and without Time Pressure might be larger than reXected by the reported means.
Manipulation checks Main dependent variable Letter combinations In general, participants did well on the letter combination task. On average each letter combination had been judged accurately (i.e., accurate identiWcation of predominance of capital or lower case letters) by 89% of 2 As a pilot study (N D 30) we conducted an awareness check (see Bargh & Chartrand, 2000) to check that participants did not consciously perceive the subliminally presented anchor value. In this awareness check, the anchor value (10 or 90, dependent on condition) is presented 15 times for 17 ms, preceded and followed by two crosses, like in the letter combinations. Participants were informed that between the crosses nothing, a word, a number or a picture was presented and participants were asked what they saw. This was repeated a second time. The third time, we again presented the anchor value for 15 times, and asked whether they saw nothing, the number 10, 30, 50, 70 or 90. Thus, the correct answers for question 1, 2, and 3, respectively, were a number, a number, and 10 or 90 (dependent on condition). In total 97.7% of the participants made one or more errors. More than half of the participants (56.7%) answered none of the three questions correctly. Another 36.7% gave only one correct answer. There was one participant (3.3%) who had two correct answers and there was only one (3.3%) who had all three answers correct. There is no diVerence in the number of correct answers between the low (M D .40) and the high Anchor condition (M D .67), F (1, 28) D 1.00, ns. So, it is safe to conclude that participants were not able to consciously perceive the subliminally presented anchor value.
We expected that in the conditions with Time Pressure, the subliminally presented anchor value would inXuence the probability estimate. Inspection of the means in Table 1 reveals that the expected pattern was obtained. A 2 (Anchor: low, high) £ 2 (Time Pressure: absent, present) ANOVA revealed a signiWcant interaction eVect between Anchor and Time Pressure, F (1, 58) D 5.06, p < .05. In the conditions with Time Pressure, participants estimate the probability of an epidemic higher in the high Anchor condition (M D 39.40) than in the low Anchor condition (M D 20.00). There were no signiWcant main eVects,
Table 1 Means (standard deviation) of the probability estimates as a function of Anchor and Time Pressure Anchor
Low High
Time Pressure Present
Absent
20.00 (19.89) 39.40 (24.63)
32.06 (24.44) 25.56 (21.23)
Note. Probability estimates are expressed in percentages. n D 15 or 16 per cell.
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Fs (1, 58) < 1, ns. Thus, the anchor eVect critically depended on whether there was Time Pressure or not. The diVerence between the high and the low Anchor condition was only signiWcant for the conditions in which there was Time Pressure, t(28) D 2.37, p < .05 and not for the conditions in which there was no Time Pressure, t(30) < 1, ns. (high Anchor condition, M D 25.56, low Anchor condition M D 32.06). This conWrms our expectations.
Discussion The results of our study indicate that there is a subliminal anchor eVect and that this eVect is short-lived. The probability estimate assimilated towards the subliminally presented anchor value in the conditions with time pressure. In the Introduction section, we described two reasons to expect an anchor eVect only in the conditions with time pressure. One reason is that in the conditions with time pressure, the time between the last subliminal presentation of the anchor value and the absolute estimate is shorter than in the conditions without time pressure. Because the accessibility level of the subliminally presented anchor value will decrease with time, the chances that the anchor value will still be activated is higher in the conditions with time pressure than in the conditions without time pressure. The second reason is that time pressure interferes with extensive recall processes and increases reliance on the Wrst thing that comes to mind. Participants will generate less candidate answers under time pressure. Thus, fewer alternative numbers are available to be combined with the anchor value into the Wnal quantitative estimate. Provided that the anchor value diVers from the alternative candidate answers, it will have more inXuence on the weighted combination of candidate answers if there are only a few (e.g., two instead of four). Consequently, the impact of the anchor value on the quantitative estimate will be larger under time pressure. One or both of these processes (less decay of the anchor’s activation level or less systematic judgment resulting in less candidate answers and relatively more impact of the anchor value) may have played a role. One way to Wnd out to what extent these processes played a role is to do a study in which two time delays are systematically manipulated (i.e., the time between the last subliminal presentation of the anchor and the presentation of the question for the absolute estimate, and the time allowed to the participants to answer this question) and also the (im)possibility to generate candidate answers. Research using the standard paradigm of anchor research, that is a combination of a comparative and a subsequent absolute judgment, has provided numerous demonstrations of strong and durable anchor eVects.
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However, not all elements of the standard paradigm are needed for an anchor eVect. There is, for instance, still an eVect when the anchor value is blatantly irrelevant for the quantitative estimate, and when the target in the comparative and the absolute judgment are not the same. Even when there is no comparative judgment and the anchor value is brieXy introduced in some superWcial way (e.g., participants have to check the color of the number), an anchor eVect emerges. However, it seems that the size and the durability of the anchor eVect decreases when elements of the standard paradigm are stripped. Our study showed that one of the Wnal elements of the standard paradigm, i.e., supraliminal presentation of the anchor value, is no prerequisite for the occurrence of the anchor eVect. This subliminal anchor eVect appears to be even more basic than the “basic anchoring” eVect found by Wilson et al. (1996). The prerequisite for Wilson et al.’s basic anchoring was a minimal amount of attention paid to the anchor value. In our experiment we demonstrated that even when participants could not pay attention to the subliminally presented anchor value, an anchor eVect still emerged. We are certain that participants could not attend to the anchor values because the presentation time (17 ms) is according to Bargh and Chartrand (2000) adequately short for stimuli, presented in the foveal visual Weld, to be truly subliminal. We think that a likely explanatory mechanism of the subliminal anchor eVect is the numeric priming account: the accessibility level of the subliminally presented anchor value (i.e., merely the number itself and not semantically related thoughts) is heightened and this leads to activation of the anchor value as a candidate answer to the probability estimate, so that this judgment assimilates towards this anchor value. Several studies have been done in which it has been suggested that anchor eVects may be caused by numeric priming (Brewer & Chapman, 2002; Jacowitz & Kahneman, 1995; Wilson et al., 1996; Wong & Kwong, 2000). Mussweiler and Strack (2001b) also report anchoring eVects due to numeric priming processes when semantic processes are incapacitated. In our study, the anchor value is presented subliminally. This is a condition atypical of the standard paradigm of anchoring. Under this condition, it is highly unlikely that participants have generated semantically related information by the subliminally presented anchor value as in the Selective Accessibility Model. While semantic priming processes cannot play a role, numeric priming processes can. Mussweiler and Strack (2001b) stated that the numeric priming processes of anchoring implies that the anchor eVect is fairly transitive and short-lived. Indeed, we found the subliminal anchor eVect to be short-lived. As far as we know, the present research is the Wrst demonstration of a subliminal anchor eVect. We think
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that the demonstration of this eVect contributes to the present discussion in the Weld of anchoring about the conditions under which an anchor eVect occurs. For decades, most research on the anchor eVect used the standard paradigm. More recently, it has been shown that anchoring also exists under conditions diVerent from the standard paradigm. Wilson et al. (1996) demonstrated the existence of basic anchoring eVects. Until recently, this was the only demonstration of the basic anchoring eVect. Brewer and Chapman (2002) performed a series of studies and replicated this eVect, although they also showed limited generality of basic anchoring. Our demonstration of a subliminal anchor eVect, where nearly all elements of the standard paradigm have been stripped, supports the existence of anchor eVects that are even more basic than previously thought. Even if a number is merely Xashed on a screen and judges are unaware of this number, their subsequent probability estimate assimilates towards this number. Although this eVect is short-lived, it is proof of the pervasive nature of anchoring. If conditions are favorable anchor eVects may dominate quantitative estimates, but even if conditions are harsh anchor eVects may still emerge. References Bargh, J. A., & Chartrand, T. L. (2000). The mind in the middle: A practical guide to priming and automaticity research. In H. T. Reis & C. M. Judd (Eds.), Handbook of research methods in social and personality psychology (pp. 253–285). New York: Cambridge University Press. Bargh, J. A., & Pietromonaco, P. (1982). Automatic information processing and social perception: The inXuence of trait information presented outside of conscious awareness on impression formation. Journal of Personality and Social Psychology, 43, 437–449. Brewer, N. T., & Chapman, G. B. (2002). The fragile basic anchoring eVect. Journal of Behavioral Decision Making, 15, 65–77. Chapman, G. B., & Bornstein, B. H. (1996). The more you ask for, the more you get: Anchoring in personal injury verdicts. Applied Cognitive Psychology, 10, 519–540. Chapman, G. B., & Johnson, E. J. (1999). Anchoring, activation and the construction of values. Organizational Behavior and Human Decision Processes, 79, 115–153. Daamen, D., de Vries, I., & Kesnich, E. (1996). Hoe robuust is het ankering- en- aanpassingseVect? Kansen op rampen in woorden en getallen en de rol van ongeloofwaardige ankerinformatie. [On the robustness of anchoring-and-adjustment. Verbal versus numerical probabilities of disasters and non-credible anchor information.] In E. van Schie et al. (Eds.), Sociale Psychologie en haar toepassingen (Reeks toegepaste sociale psychologie, deel X). Delft: Eburon. Dehaene, S., Naccache, L., Le Clec’H, G., Koechlin, E., Mueller, M., Dehaene-Lambertz, G., et al.(1998). Imaging unconscious semantic priming. Nature, 395, 597–600. Dijksterhuis, A., Aarts, H., & Smith, P. K. (2003). The power of the subliminal: On subliminal persuasion and other potential applications. In R. Hassin, J. S. Uleman, & J. A. Bargh (Eds.), Unintended thought 2: The new unconscious. New York: Oxford University Press. Englich, B., & Mussweiler, T. (2001). Sentencing under uncertainty: Anchoring eVects in the courtroom. Journal of Applied Social Psychology, 31, 1535–1551.
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