Slow lies: response delays promote perceptions of insincerity

Evaluating other people’s sincerity is a ubiquitous and important part of social interactions. Fourteen experiments (total N = 7565; ten preregistered; eleven in the main paper, three in the SOM; with U.S. American and British members of the public, and French students) show that response speed is an important cue on which people base their sincerity inferences. Specifically, people systematically judged slower (vs. faster) responses as less sincere for a range of scenarios from trivial daily conversations to high stakes situations such as police interrogations. Our findings suggest that this is because slower responses are perceived to be the result of the responder suppressing automatic, truthful thoughts, and fabricating a novel answer. People also seem to have a rich lay theory of response speed, which takes into account a variety of situational factors. For instance, the effect of response delay on perceived sincerity is smaller if the response is socially undesirable, or if it can be attributed to mental effort. Finally, we showed that explicit instructions to ignore response speed can reduce the effect of response speed on judgments on sincerity. Our findings not only help ascertain the role of response speed in interpersonal inference making processes, but also carry important practical implication. In particular, the present study highlights the potential effects that may be observed in judicial settings, since the response speed of innocent suspects may mislead people to judge them as insincere and hence guilty.