Friends of the Behavioral Economics Blog, this week we present the paper “Monetary incentives do not reduce the repetition-induced truth effect” by Speckmann, F. and Unkelbach, C. (2022) in which the authors carry out an experiment to know whether the introduction of financial incentives affects when it comes to distinguish between a lie and a truth, specifically, considering the repetition-induced truth effect. 

People see, read and hear many different events and statements every day (news, social networks, conversations…) that they may doubt or believe.

Apparently, people use repetition as a signal to lean one way or the other when it comes to making a decision about the veracity of what they hear. Therefore, they tend to believe statements that are repeated more, compared to statements that are repeated less. 

This phenomenon is known as the illusory truth effect, truth by repetition, or simply the truth effect.

In a paper by Hasher in the 1970s, participants were presented with a total of 60 statements. Half of them were false and half were true. The participants were exposed to them in two sessions. During each of these, 20 of the 60 statements were repeated, and the remaining 40 were newly introduced. That is, 20 of the 60 statements were shown in the two sessions. After the presentation phase in each session, participants were asked to rate the validity of each statement. The participants judged the repeated statements as more valid and credible than the new statements, which demonstrated the basic truth effect. 

The effect has gained more prominence in recent years, as it may serve as an explanation for people’s belief in conspiracy theories, misinformation and fake news, due to the frequent repetition of false information on the internet and social networks. 

In this study, the authors investigate what happens if, when a decision has to be made, economic incentives must be taken into account. That is, what happens when, when choosing between qualifying a statement as true or false, a certain amount of money is gained or lost, depending on whether one gets it right or wrong. 

In other words, they asked whether the repetition-induced truth effect persists if participants’ decisions are highly financially incentivized. 

The fact that incentives diminish the truth effect would suggest that the real-life impact of repeating information is not as critical as it seems. 

However, if monetary incentives do not reduce the truth effect of repetition, it would underline the relevance of the phenomenon in real life. At the theoretical level, it would show that people potentially consider repetition as a valid cue for making their decisions. 

In the experiment, the authors used 120 statements, 60 of which were true and 60 false. They recruited a total of 321 people. They divided them into three groups: the high-incentive group (they could earn up to 12€), the medium-incentive group (they could earn up to 6€), and a final group with no incentives. However, all three groups were told that they could earn a maximum of €4. 

For each statement, they had to indicate whether they considered it true or false. They did not know this, but for each correct answer they would receive €0.10 and for each false answer they would lose €0.10, and could never get negative results. 

Although some participants could receive up to €12 and others up to €6, it seems that the incentives did not substantially influence the repetition-induced truth effect. 

Using an exploratory contrast, the authors found a slight difference in the truth effect between the “no incentive” conditions and the “with incentive” conditions: participants showed a slight reduction in their tendency to judge repeated information as true, but the effect was very small in size, so it is not considered strong evidence. 

Significant differences occurred, however, when it came to response time. Being shorter, it seems logical to think that participants were motivated to answer correctly as often as possible to increase their gains. 

The results are consistent with others obtained in previous literature, and illustrate the robustness of the repetition-induced truth effect by showing that, even when adding direct consequences to truth judgments, there is no change in people. 

Thus, the data support existing cognitive explanations of the repetition-induced truth effect, with potential implications for real-world phenomena that have been explained for some time now, such as belief in fake news, conspiracy theories, among others. 

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