Introduction

In recent years a substantial body of evidence has accumulated which suggests that behaviour can be unconsciously influenced or primed by the activation of relevant stereotypes, attitudes, traits, goals, or other concepts. Instead of, or in addition to, the normal route from conscious intentions to behaviours, individuals can be induced (it is claimed) to act socially or unsocially, walk faster or slower, behave more or less intelligently, or perceive accurately or inaccurately as a result of subtle priming influences of which they are unaware. Bargh, Chen, and Burrows, for example, asked participants in one study to read sentences containing words related to the concept old age and reported that a few minutes later these individuals walked more slowly down a corridor [1]. Another study reported that participants judged a hill as steeper when they were wearing a heavy backpack [2]. Equally striking, and the focus of the present research, is Dijksterhuis and van Knippenberg's report that individuals answer more general knowledge questions correctly after being asked to think about the attributes of a professor than they do after thinking about soccer hooligans [3].

Understanding the principles of behaviour change is fundamental to psychology. Consequently, demonstrations such as these call into question the standard view that the best way to effect behaviour change is through alterations to conscious beliefs and intentions. Those involved in this research have made bold statements about its importance. Bargh and Huang [4], for instance, wrote:

“Priming” refers to the passive, subtle, and unobtrusive activation of relevant mental representations by external, environmental stimuli, such that people are not and do not become aware of the influence exerted by those stimuli. In harmony with the situationist tradition, this priming research has shown that the mere, passive perception of environmental events directly triggers higher mental processes in the absence of any involvement by conscious, intentional processes…” (p. 128)

On the other hand, from the perspective of cognitive psychology, these effects are more than a little surprising. A well-established principle in traditional priming research (which commonly involves presenting words as primes to study lexical or semantic processing) is that generalization is often extremely narrow and context-specific [5]. If the priming effects of reading a word such as OLD do not transfer across changes in font or modality, then how likely is it that they transfer to something like speed of walking? The priming effects described above are unusual in this context as they imply effects which generalize very broadly. Another reason these reports are surprising is that decades of research has found that unconscious or subliminal influences on behaviour are exceptionally difficult to demonstrate [6], [7], [8], and even when replicable positive effects are shown, they tend to be over extremely short time intervals (less than a second), far shorter than the intervals involved in the studies described above, where periods of at least a few minutes are involved.

The experiments described in this article arose from an initial desire to probe more deeply into claims that the aforementioned goal priming effects are unconscious. Our intention was to use more sensitive measures of awareness to investigate the extent to which participants are truly unconscious of the influence of the prime on their behaviour in tasks where priming a concept related to intelligence (Professor or Soccer hooligan) has been reported to affect performance on a subsequent test of general knowledge. Note that the present focus on activation of other-related stereotypes (stereotypes of groups of which one is not a member) excludes studies within the ‘stereotype threat’ literature in which activation of self-related stereotypes (such as ‘African American’ for African American participants) is found to reduce academic performance [9]. In contrast to the studies reviewed here, stereotype threat research tends to assume that the effects of activating a self-related stereotype are consciously mediated and arise through raised state anxiety [10]. Another difference is that the stereotype threat effect is negative compared to a neutral control condition whereas intelligence priming can be both positive and negative.

We found it difficult, however, to replicate the basic effect of stereotype priming on accuracy in answering general knowledge questions. Our efforts to determine the reasons for this difficulty are described here, together with a Bayesian analysis of our findings [11]. This provides a precise quantitative evaluation, given a level of prior belief in the intelligence priming effect, of the posterior odds of the null hypothesis (no priming effect) against the experimental hypothesis (intelligence can be primed).

Experiments 1–4

Dijksterhuis and van Knippenberg's [3] task involved a between-subjects manipulation. Some participants spent a few minutes describing the attributes of a typical professor, whereas others described those of a typical soccer hooligan. Specifically, they were asked to imagine a typical professor (or soccer hooligan) and to list the behaviors, lifestyle, and appearance attributes of this typical professor (or soccer hooligan). Participants then performed what was presented as an unrelated multiple-choice general knowledge test. Dijksterhuis and van Knippenberg reported that priming the stereotypes of professor (Experiments 1 & 2) or soccer hooligans (Experiment 3) affected performance on the general knowledge task, with the former leading to improved performance and the latter to worse performance. The same effect on behaviour was shown when, instead of thinking about a typical professor or soccer hooligan, participants were asked to think directly about the traits intelligence or stupidity (Experiment 4). Furthermore, there was evidence that the priming effect increased when the prime phase was longer (9 min vs 2 min).

Dijksterhuis and van Knippenberg [3] suggested that the priming effect occurs because activation of the stereotype of intelligence (in the professor compared to the soccer hooligan condition) leads participants to use more intelligent strategies for answering the questions, or motivates them to concentrate harder, or increases confidence and hence induces a beneficial response bias. The range of possible mechanisms is discussed elsewhere [12], [13].

The first four experiments reported here attempted to replicate the basic intelligence priming effect using procedures similar (Experiments 1 and 2) or identical (Experiments 3 and 4) to those used in the original study describing the effect.

Results

Across the experiments reported here, some participants reported in debriefing that the priming procedure might have influenced their performance in the knowledge test (see Supporting Information for details). However these reports were often vague and inconsistent with the experimental hypothesis: for instance, some participants in the soccer hooligan prime conditions reported that listing attributes about the stereotype helped them to concentrate and perform better in the general knowledge task. None of the results in any of the experiments were altered by the exclusion of these participants, and hence we report results across all participants.

To investigate the change in test performance following priming a difference score was computed for Experiments 1 and 2, by subtracting the baseline score from the post-priming score. The mean difference scores for both Experiments 1 and 2 are shown in Table 1 (effect sizes are reported in Table 2) and suggest that there was an improvement in performance in both groups, representing a benefit of practice. However, contrary to predictions, the improvement was no greater in the professor than in the hooligan condition: in fact it was the other way round in both experiments, though the mean improvement scores did not differ either in Experiment 1, t(38) = −1.10, p = .14, or in Experiment 2, t(14) = −0.18, p = .43 (because we are testing directional predictions, all reported p values are 1-tailed).

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Table 1. Experimental results.

https://doi.org/10.1371/journal.pone.0056515.t001

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Table 2. Bayesian t-test analyses.

https://doi.org/10.1371/journal.pone.0056515.t002

For Experiment 3 there was no pre-test and hence the key data are raw scores (percentages correct) on the general knowledge test. The analysis revealed that there was no significant difference between the two conditions, t(42) = 0.45, p = .33. Experiment 4 yielded no evidence of stereotype priming either, t(98) = .57, p = .28. Note that these experiments employed sample sizes comparable to or larger than those employed by Dijksterhuis and van Knippenberg [3]: their groups varied in size from approximately 10 to 32. Experiment 4 included more participants (50 per group) than any of the published studies.

Failures to obtain significant effects (null results) are often regarded as inconclusive in psychological research. Yet from a Bayesian perspective there is little difference in the status of an experimental hypothesis versus the null hypothesis, in the sense that in both cases it is meaningful to define the probability of the data given the hypothesis. A considerable body of recent research has sought to develop methods for quantifying these probabilities and, in particular, for comparing them in a likelihood ratio [11], [17]. Specifically, a “Bayes factor” is defined as the ratio of the probability of the data given the null hypothesis versus the probability of the data given the experimental hypothesis. This likelihood ratio, when multiplied by the prior odds, yields the posterior likelihood ratio of the null versus the experimental hypothesis, given the data. When this odds ratio is very small, such as 1∶10, then one can infer that the evidence strengthens the experimental hypothesis by a factor of 10, regardless of one's prior belief about the likelihood of the experimental hypothesis being true. Conversely, when the odds ratio is very large (e.g., 10∶1) then the evidence strengthens the null hypothesis by a factor of 10, again regardless of prior beliefs. We report later a full Bayesian analysis of our findings, but as a preview we note that the results of Experiments 1–4 yield Bayes factors of between 2.54∶1 and 5.58∶1 in favour of the null (see Table 2). Thus each experiment suggests an approximate trebling of the posterior probability of the null hypothesis being true, compared to the experimental hypothesis. Our subsequent analysis also includes a description of the cumulative odds ratios based on all our experimental data.

In light of these failures to obtain intelligence priming, we conducted a thorough literature review to identify all priming studies published subsequent to the original reports of Dijksterhuis and colleagues which obtained an influence of stereotype activation on some measure of knowledge or intelligence [3], [14], [18]. One study [16] employed the same task and procedure as Dijksterhuis and van Knippenberg [3] with the exception that the primes were professors and cleaning ladies, while another used professor and soccer player primes [19]. Three further reports using modifications of the original method were also identified [20], [21], [22]. The following experiments attempt to replicate the findings of these latter reports. A further study [23] obtained a nonsignificant assimilation effect (see Discussion).

Experiment 5

The basic intelligence priming obtained by Dijksterhuis and van Knippenberg [3] is an assimilation effect in the sense that the participant's behavior purportedly comes to resemble that of the prime (professors behave intelligently, soccer hooligans unintelligently). More recently, it has been suggested that the behavioral effects of abstract social concepts such as stereotypes are not always assimilative. Instead, behavior can be shifted in the opposite direction to the activated concept. Such behavioral contrast, like assimilation, takes place following a priming procedure but only in the presence of several moderating factors assumed to trigger social comparison.

An initial suggestion was that while priming the stereotype of professors or supermodels leads to behavioral assimilation, priming exemplars such as Albert Einstein (i.e., an intelligent exemplar) or Claudia Schiffer (i.e., a purportedly low-intelligent exemplar) leads to behavioural contrast, revealed as worse performance and improved performance, respectively, in the subsequent general knowledge test [18]. The category/exemplar contrast was subsequently found, however, not to be the key variable. LeBoeuf and Estes ([22], Experiment 1) tested and found support for the alternative hypothesis that, irrespective of whether it was a category or an exemplar, a prime could produce both behavioural assimilation and contrast depending on how relevant a comparison standard it was perceived to be. Comparison relevance was manipulated by asking participants to list either similarities (high relevance) or differences (low relevance) between themselves and the prime, the idea being that listing self-prime similarities would promote consideration of the prime as a relevant comparison standard and listing self-prime differences would lead to discounting the prime as a relevant comparison standard. Different groups of participants were asked to list how similar to (high relevance) or how different from (low relevance) either professors (category prime) or Einstein (exemplar prime) they thought they were. Immediately following the priming manipulation, they were asked to answer multiple-choice general knowledge questions. The results showed that participants in the low-relevance conditions (where they listed differences) performed better than the participants in the high-relevance conditions (where they listed similarities).

LeBoeuf and Estes' interpretation of this outcome proposed that when participants in the low-relevance condition listed differences between themselves and either professors or Einstein, they activated the general trait of intelligence associated with the primes [22]. However, because they discounted the primes as relevant comparison standards, they demonstrated assimilation. Participants in the high-relevance conditions, however, listed similarities which induced them to compare themselves with professors or Einstein, leading to worse performance, and hence, behavioural contrast. The greatest difference was between the groups that listed self-professor similarities and self-Einstein differences, the latter performing substantially better than the former. In a follow-up experiment, LeBoeuf and Estes replicated the difference between these two groups ([22], Experiment 2). In a further experiment (Experiment 3) they replicated Dijksterhuis et al.'s [18] finding that performance was better after listing attributes of a category (Professor) than of an exemplar (Einstein), while again showing that generating self-Einstein differences led to better performance than generating self-professor similarities.

Experiment 6

What might explain the difference in results between LeBoeuf and Estes' [22] study and the previous study? We went to considerable lengths (e.g., via the cover stories) to eliminate any sort of demand effects. An obvious possibility is that demand effects were responsible for the different results in the two studies. If the participants in LeBoeuf and Estes' study – but not in Experiment 5 – detected the true purpose of the study and inferred the experimental hypothesis, this might account for the different results [24].

In Experiment 6, therefore, participants were explicitly told the experimental hypothesis and the expected direction of the effect the priming manipulation might have on their performance in the general knowledge test. Specifically, participants in the Einstein-differences condition were told that thinking about Einstein was expected to increase their performance in the general knowledge test whereas those in the professor-similarities condition were told that comparing themselves to a professor was expected to decrease their performance. If, under these conditions, it was found that there was a significant effect of the priming manipulation on the direction of performance, it would be safe to assume that demand effects did indeed have a role to play in producing these results.

Experiment 7

In a further elaboration of possible moderators of assimilation and contrast, Gordijn and Stapel provided evidence that whether social comparisons lead to automatic contrast or assimilation effects on behaviour depends on whether the comparison target is categorized as an in-group or out-group member [21]. Gordijn and Stapel hypothesized that if an intergroup context is made salient, where social identity becomes more salient than one's personal identity, assimilation should occur when the activated comparison target is perceived as an in-group member. If, however, the target is perceived as an out-group member behavioural contrast should occur.

In accordance with this hypothesis, Gordijn and Stapel [21] demonstrated an in-group/out-group effect on the direction of priming. In their study, an intergroup context was made salient by telling participants, who were students at the University of Groningen, that their findings would be compared with the findings from students at the University of Amsterdam. Then, for the priming procedure, they were asked to form an impression and rate on several personality traits a person who was described as either highly intelligent or unintelligent. Also, to manipulate the social identity of the comparison target, the target person was described as either a former student from the University of Groningen (i.e., in-group) or from the University of Amsterdam (i.e., out-group). Subsequently, participants were given a purportedly unrelated general knowledge test. In line with Gordijn and Stapel's prediction, priming with in-group comparison targets led to behavioural assimilation (i.e., enhanced performance with the intelligent target and poorer performance with the unintelligent target) while out-group comparison targets led to behavioural contrast (i.e., poorer performance with the intelligent target and enhanced performance with the unintelligent target). This implies that the social identity (in-group vs. out-group) of a comparison target can moderate the direction of automatic behaviour.

In a further effort to obtain an intelligence priming effect, we attempted to replicate Gordijn and Stapel's study. Their article [21] was retracted after the completion of Experiment 7 and hence their data can be given no evidential weight. Nevertheless, the hypothesis they put forward is a reasonable one and thus we report Experiment 7 in relation to that hypothesis. Note that another report on intelligence priming has also recently been retracted [25]. An intergroup context was made salient by informing participants (students from University College London [UCL]) that their results would be compared with the results of students from Birmingham University, where the same experiment was being run. The priming manipulation involved asking participants to form an impression of a person who was described as either a professor or soccer hooligan and who was either a former student from UCL or from Birmingham University. Thus assimilation to the comparison target is expected when the target is categorized as an in-group member, whereas contrast should occur when the target is perceived as an out-group member.

Experiment 8

In light of these failures to detect any reliable priming effects, Experiment 8 aimed to explore whether it is possible to affect general knowledge test performance by a different manipulation, monetary incentives. It is well known that incentives and rewards can motivate subjects to participate in experiments in a more effortful and considered fashion and to improve their performance against some standard [26]. In a meta-analysis of published studies, incentives were found to have a medium-sized effect on IQ performance [27] and effects of incentives on a range of measures of educational performance in classroom settings have been reported [28]. Thus, incentives may motivate participants to employ more cognitive effort in a general knowledge task. The present experiment therefore tests the hypothesis that if intelligence priming can improve general knowledge ability through increased motivation, then so too should explicit reward.

The experiment included 4 groups. Two of these performed the general knowledge test under incentives or no incentives with no priming phase. Two further groups performed the test after the standard positive (professor) or negative (hooligan) priming induction in a further attempt to replicate the basic intelligence priming effect.

Experiment 9

Yet another variation on the basic intelligence priming effect was reported by Bry, Follenfant, and Meyer [20]. These researchers considered the moderating influence of self-construal on contrast and assimilation. ‘Self-construal’ refers to the way in which the self is mentally represented and can vary from independence, when the individual thinks of herself as unique, autonomous, and distinct from others, to interdependent, when she conceptualizes herself as connected to others and part of a larger group. Bry et al. proposed that assimilation to an intelligent or unintelligent prime would occur under interdependence and that contrast would occur under independence, and obtained experimental support for this pattern.

To test this hypothesis, participants in Bry et al.'s Study 2 [20] initially rated themselves in relation to a series of statements designed to evoke independence (e.g., “I am unique – different from others in many respects”) or interdependence (e.g., “to understand who I am, you must see me with members of my group”). This was followed by a priming phase in which participants answered questions about a series of faces. Bry et al. activated the ‘dumb blonde’ stereotype by including a large proportion of faces of blonde-haired females. Finally, participants answered general knowledge questions. Bry et al. found reliable assimilation (worse performance after priming the stereotype Blonde than after no priming) under the interdependent self-construal and contrast (better performance after priming the Blonde stereotype than after no priming) under independence.

We closely replicated Bry et al.'s procedure [20], but used the professor/soccer hooligan stereotypes as well as a no-prime control condition. Specifically, participants in the primed groups answered questions about pictures of professors or soccer hooligans. For full details see the Supporting Information.

Bayesian Comparison of the Null and Experimental Hypotheses

As noted earlier, traditional statistical methodology regards failures to reject the null hypothesis as inconclusive. Indeed, in Fisherian statistics “every experiment may be said to exist only in order to give the facts a chance of disproving the null hypothesis” ([29], p. 19). The null hypothesis significance testing approach has been severely criticized, however, because it invites a number of fallacious inferences, such as that rejection of the null hypothesis is equivalent to affirmation of the experimental hypothesis, that p-values provide measures of evidential support, and that they represent the probability that the null hypothesis is true [30]. In response to these concerns, Bayesian approaches have been developed which regard the experimental and null hypotheses as on an identical footing in terms of their ability to be evidentially supported or disconfirmed and which, of particular importance, allow one to evaluate evidence for the null hypothesis from a given experiment or set of experiments [11], [17]. See [31] for a recent application of these methods in another domain where unconscious influences have been hypothesized.

We used the method described in [11] to compute a Bayes factor for each experiment, defined as the ratio of the probability of the data given the null hypothesis to the probability of the data given the experimental hypothesis. To compute these factors, it is necessary to specify the form of the distribution of possible effect sizes under the experimental hypothesis. Two candidates are the normal and Cauchy distributions. The Cauchy prior makes weaker assumptions about the likely effect sizes under the experimental hypothesis and is therefore preferred, although we report results based on both. Although the experiments were conducted for the purpose of testing directional hypotheses, we report two-tailed Bayes factors because – as the reports of assimilation and contrast indicate – an effect in either direction could be interpreted as evidence of priming.

The Bayes factor for a given experiment, when multiplied by the prior odds, yields the posterior likelihood ratio of the null versus the experimental hypothesis, given the data. It is important to note that the interpretation of a given Bayes factor is independent of one's predispositions regarding the ex ante probability of the experimental hypothesis being true. Suppose a researcher is strongly predisposed to believe that intelligence can be primed in the situations studied here; perhaps her belief is that the experimental hypothesis is 10 times more likely than the null hypothesis (odds null∶experimental of 1∶10, equivalent to a probability of p = .91 of the experimental hypothesis being true). After observing data from an experiment which yields a Bayes factor of 2∶1, this researcher should rationally adjust her odds to be 2∶10 ( = 1∶5). Consider in contrast another researcher who is strongly predisposed to doubt that intelligence can be primed; let us imagine that he believes that the experimental hypothesis is 10 times less likely than the null hypothesis (odds null∶experimental of 10∶1, equivalent to a probability of p = .09 of the experimental hypothesis being true). After observing the same data from an experiment with a Bayes factor of 2∶1, this researcher should adjust his odds to be 20∶1. In both cases the posterior odds have changed by the same factor of 2∶1.

Table 2 presents the effect sizes, t and p-values, and Bayes factors for each relevant comparison. We treat the in-group and out-group contrasts in Experiment 7 as if they were independent experiments, and similarly for the independent and interdependent contrasts in Experiment 9 (where in addition we ignore the no prime groups). The table shows that for each experiment, the null gains at least twice as much support as the experimental hypothesis, and for 6 of the contrasts (Cauchy) the Bayes factor is greater than 3. A Bayes factor of between 1∶1 and 3∶1 is taken to provide ‘anecdotal’ evidence in favour of the null, whereas factors of between 3∶1 and 10∶1 provide ‘substantial’ support [32]. A meta-analysis across all experiments (with the data z-transformed within each experiment) yields a Bayes factor of 12.1, representing strong support for the null.

Discussion

We investigated here the claim that priming the concept of intelligence can influence behaviour. This claim is important not only because of its theoretical implications [4] but also because of the possibility that performance in significant applied settings, such as taking classroom exams, can be boosted by unconscious priming [33]. However the results reported here suggest that priming the concept ‘Professor’ (versus ‘Soccer hooligan’) confers no advantage in answering general knowledge questions. Activating the concept or goal of intelligence via priming a related concept does not appear to increase intelligence in these experimental conditions. The Bayesian analysis reported here suggests that considerable confidence can be placed in this null hypothesis.

Why might we have obtained results so different from previous published findings? One possibility is that our priming manipulations were simply ineffective. This however seems unlikely. The stereotypes (professor/soccer hooligan) are well entrenched in the minds of our participant population, and we closely followed the original protocols in the published studies. It is noteworthy that the types of priming manipulation reported previously to be successful have varied quite widely in their format; for example, while Dijksterhuis and van Knippenberg's participants [3] considered the attributes of the prime target for several minutes, LeBoeuf and Estes [22] observed a priming effect with the standard attribute-listing methodology when participants merely listed 3 attributes, which may have taken only a few seconds. Participants in Bry et al.'s study [20] simply reported the hair color of a series of individuals shown in pictures. Thus studies reporting positive priming effects have done so across wide variation in the priming procedure.

A second possibility is that the knowledge tests we used were different in some subtle but key way from those employed elsewhere. Against this, however, is the fact that we modelled our tests on those used previously (in Experiment 5, for instance, we used many of the same questions that LeBoeuf and Estes had employed) and we ensured similar levels of overall difficulty. In addition we used a wide range of test questions, including non-overlapping tests across our experiments, as well as different forms of assessment (Raven's matrices). Moreover we were able to affect performance via monetary incentives (Experiment 8). Thus the general knowledge test was not entirely insensitive.

A third possibility is that previous studies have yielded priming effects because compliant participants were able to infer, and hence behave in accordance with, the experimenter's hypothesis [24]. Although such a possibility would undermine the theoretical significance of the effect, it would nonetheless imply that it should be replicable. Perhaps for some reason our participants did not respond in this way to the task demands. Our early failures to obtain intelligence priming encouraged us to take this explanation seriously, especially in light of other recent evidence: in another priming situation, it was reported that participants judged a hill as steeper when they were wearing a heavy backpack [2], but a later study found evidence that this is an artefact of compliance by participants to the perceived experimental hypothesis [34]. The results of Experiment 6, however, provide little support for this possibility within the intelligence priming task. An explicit instruction as to the nature of the experimental hypothesis failed to yield priming. Nevertheless, subtle differences between the present experiments and previous ones may have affected participants' detection of and compliance with task demands. The method employed in Experiment 6 to induce compliance may have been inadequate, and the failure to induce priming in that experiment does not categorically rule out the possibility that participants in previous demonstrations of intelligence priming were reacting to the perceived task demands. Future research could profitably explore alternative methods to vary compliance levels.

A fourth possibility is that our experiments lacked sufficient power to detect small but real intelligence priming effects. The Bayesian analysis reported above takes sample sizes into account and hence its conclusion indirectly reflects experimental power: for a given t-statistic, the Bayes factor increases with sample size. Conventional power analysis therefore becomes redundant, but we comment briefly on power nonetheless. Published effects have been uniformly large to very large in terms of effect size. Effect sizes in the original experiments reported by Dijksterhuis and van Knippenberg [3] ranged from 0.83 to 1.35. In Dijksterhuis and van Knippenberg's [14] Experiment 2 the effect size (Cohen's d) was 2.11, in Hansen and Wänke's [16] Experiment 2 d = 0.76, and in Nussinson et al.'s [19] Study 3 d = 0.84. In LeBoeuf and Estes' [22] Experiment 2 the comparison between scores in the self-professor similarities and self-Einstein differences groups had d = 0.72. In Bry et al.'s [20] Study 2, the priming effect size for the independent self-construal was d = 0.88 and for the interdependent self-construal was d = 0.79. These are strikingly large effects (mean d = 1.05, median = 0.86). Naturally, some of the individual experiments or comparisons reported here had low to moderate power. However, Experiment 4 was specifically conducted to provide a near-exact replication of the published method with a large sample size (larger than used in any of the published studies), and that experiment alone had ample power to detect effects of the magnitude noted above: it had power of 1 - β = .99 to detect a large effect (i.e., d = 0.8) and power of .80 to detect a medium-sized effect (i.e., d = 0.5). Across all the relevant comparisons (Experiments 1–5 and 8, the in-group/out-group contrasts in Experiment 7, and the independent/interdependent self-construal contrasts in Experiment 9), the cumulative β (i.e., the probability of all comparisons failing to detect a true large effect, d = .8, one-tailed) is approximately p = 10⁻⁷. The equivalent value for failing to detect a true medium effect (d = .5) is p = .002. Hence whatever the reason for our failure to obtain priming effects, low power does not seem a plausible explanation.

Conclusion

We do not deny outright the possibility of unconscious influences on behavior, and obviously the present experiments only relate to one particular type of priming and one particular behavior. However the present results are consistent with many other examples where claims of unconscious influences have not withstood subsequent scrutiny: for a small sample of relevant instances, see [31], [48], [49], [50], and for a comprehensive recent review see [51]. It is never possible to recreate exactly the conditions of previous experiments but if intelligence priming effects are as important as some claim them to be (and as large), then they ought to withstand minor variations in procedure, otherwise we have little prospect of understanding their basis and it is unclear why they should be afforded substantial theoretical significance. From the perspective of the cognitive priming literature, in which such effects tend to be very narrow and context-specific, the absence of an effect in the present studies is entirely unsurprising. Of course the typical procedures employed in cognitive and social priming experiments are often very different and they tend to focus on different forms of awareness (awareness of the prime in the former case and awareness of the influence of the prime in the latter case; see [51] for an extensive discussion), but the convergence of findings is noteworthy. The current results are also consistent with the view that conscious thoughts are by far the primary driver of behavior [52] and that unconscious influences – if they exist at all – have limited and narrow effects.

The theoretical and practical implications of intelligence priming are considerable. It is important that these elusive effects are studied further in independent laboratories to try to determine under what conditions they might be obtained.

Supporting Information

Acknowledgments

We thank Ruud Custers, Gregory Francis, Hal Pashler, and Piotr Winkielman for helpful discussions.