People are biased towards believing that what others say is what they truly think. This effect, known as the truth bias, has often been characterized as a judgmental error that impedes accuracy. We consider an alternative view: that it reflects the use of contextual information to make the best guess when the currently available information has low diagnosticity. Participants learnt the diagnostic value of four cues, which were present during truthful statements between 20% and 80% of the time. Afterwards, participants were given contextual information: Either that most people would lie, or most would tell the truth. We found that people were biased in the direction of the context information when the individuating behavioral cues were non-diagnostic. As the individuating cues became more diagnostic, context had less to no effect. We conclude that more general context information is used to make an informed judgment when other individuating cues are absent. That is, the truth bias reflects a smart guess in a low diagnostic world.Keywords: Adaptive decision-making; Adaptive Lie Detector; Context; Lie detection; Truth bias; Truth-default theory.
4People make for poor lie detectors. They hit an accuracy rate comparable to a coin toss, only marginally above chance (Bond & DePaulo, 2006). That might in part be because they come with a set of systematic biases that can reduce accuracy (see Burgoon & Buller, 1994; Gilbert, 1991;O'Sullivan, 2003;Vrij, 2008), such as being biased towards believing others are telling the truth more often than they actually are (Bond & DePaulo, 2006; McCornack & Parks, 1986). This article argues that the pessimistic view of lie detection is outdated and misguided: Instead we argue that people make smart judgments from the unreliable information available to them.Specifically, it is argued that the systematic biases are not sources of error, but are actually markers of a smart system making informed judgments.Although people are thought to be poor lie detectors, this stands in stark contrast to research showing that people are skilled at understanding what others are thinking.They have successful strategies to understand internal thoughts, drawing from even the subtlest of clues (e.g., from allusions in speech to eye direction: Clark, 1996; Clark, Schreuder & Buttrick, 1983;Tomasello, 1995; but see Heyes, 2014, for strategies that give only the illusion of representing others' minds), and these work only because the two parties choose to communicate with each other, producing behaviors that indicate their true thoughts. When one party wants to conceal what he or she truly thinks, these cues are not produced, or are at least drastically reduced.Accuracy is capped by the fact that speakers have good control over their behavior and do not give clear signs to their concealments and deceptions (DePaulo et al., 2003; Sporer & Schwandt, 2006, 2007. So we must ask how it is that people make any sort of social judgment when the immediately available cues have low diagnostic value. Put...