Only half of what I’ll tell you is true: how experimental procedures lead to an underestimation of the truth effect

2018-07-30Ambiguous information is judged to be more true when it has been seen or heard repeatedly than when it is new. This “truth effect” has important consequences in the real world, where we are repeatedly exposed to information that may or may not be true as we scroll through social media, read the news, or talk with friends or coworkers. Yet, while false information in the real world rarely comes with a warning label, false information in truth effect experiments often does. Commonly used experimental procedures draw attention to the truth value of claims at exposure through instructional warnings, alerting participants to potential falsehoods and limiting the impact of repetition. Three experiments show that the size of the truth effect increases by a factor of 2 to 5 times when such warnings are avoided. The effect of pre-exposure warnings on later truth judgments persists even after a delay of three to five days. These findings highlight that the most common experimental procedures systematically underestimate the likely size of the truth effect in the real world