Discussion

Our results illustrate that the mental priming force significantly influenced participants’ choice among a large number of alternatives, and it works just as effectively when presented on video compared to when it is performed by a real person.

Eighteen percent of our participants chose the target card, and most were oblivious to the force itself. Indeed, even though the force resulted in a ninefold increase chance of participants choosing the three of diamonds, participants reported that their choice was free and that they were in control of it. Investigating the way implicit cues unconsciously influence people’s thoughts provides important insights into the nature of human cognition. However, in the last decade, many priming studies have been at the center of the replication crisis (21⇓–23), and the difficulty to replicate a number of well-known effects has raised much skepticism about priming more generally. At this point, we would like to note that we have investigated the mental priming force several times and with large sample sizes and always found it to be effective (SI Appendix). For example, another unrelated study involving 240 participants showed that 15.4% of participants chose the three of diamonds (most frequently chosen card) and 33.8% chose a card with the number three.

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Naturally embedding primes within a person’s speech and gestures effectively influenced people’s decision making. Despite the primes being fully visible (and audible), participants were unaware that the primes may have influenced their decisions. Our results dovetail findings from choice blindness literature, which illustrates that people often do not know the real reason for their choice (24⇓⇓–27).

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We believe that most forcing principles can be applied to decision-making processes that are not restricted to playing cards. For example, research from our laboratory shows that some psychological principles applied to card forces generalize to contexts where people have stronger preferences [e.g., holiday destinations†] or the outcome of a computer game. With regards to the mental priming force, others have shown that misinformation from gestures can also influence eyewitnesses’ memory reports (28, 29) and that gestures could prime words (30). Despite their implicit nature, these nonverbal cues can influence both memory and decision-making processes in contexts outside the magic performance.

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Our study shares some of the characteristics of previous research on social psychological priming and embodied effects, which have been heavily criticized and found hard to replicate (31⇓⇓–34): our primes were naturally embedded within the context of the experiment. However, the cognitive mechanisms that are being activated seem to differ. As Newell and Shanks (1) point out, standard priming effects such as lexical and repetition priming rely on well-established cognitive mechanisms, but it is often difficult to explain embodied priming effects on theoretical grounds. We appreciate that further research is required to help understand the cognitive mechanism that underpins the mental priming force, but we believe that it relies on semantic priming. Several studies have shown that people process specific gestures semantically (35⇓–37), and it is likely that they evoke similar semantic activation that is found for words or pictures (38). We therefore suggest that the mental priming force relies on gestures and speech segments evoking simple semantic activation that make the number three and diamond shape more accessible.

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The mental priming force is less reliable than most other forcing principles (14⇓–16, 39, 40), and it is rarely used by magicians. Nevertheless, it was surprisingly effective. Although magicians often rely on more powerful tricks, they always have a “way out” for tricks relying on small probabilities of success rate like this one. Most conjuring techniques are very reliable, and we have investigated a wide range of forcing techniques (16, 39, 40)‡ that are far more reliable than the mental priming force. However, as we mentioned, previous findings have, for example, shown that gestural misinformation (i.e., subtle hand gestures) can influence an eyewitness testimony and implant false memories about objects that are associated with the gesture (i.e., a specific jewelry such as a bracelet or ring) (28) and that words (e.g., bird) could be primed through iconic gestures (e.g., a pair of hands flapping) (30). Our results, using the force, add to these findings and confirm that forcing techniques provide a reliable way of studying diverse mental processes (41). Moreover, our results, linked to these findings, raise the possibility that this form of mind control could be used to effectively manipulate other mental processes such as memory and word retrieval.