Laypersons and professional lie detectors differ in biases of credibility judgment. The former are biased toward the truth, whereas the latter are biased toward lies. In an attempt to further understand these differences, the present study focused on the process of credibility
judgment, rather than on its outcome. Forty-nine professionals (27 officers, 11 interrogators, 11 intelligence and secret services agents) and 40 laypersons (students) read an account of an event, and judged the credibility of the narrator; namely, the likelihood that he had actually experienced
the event. Laypersons tended to believe the narrator more than professionals. The two groups also differed from each other in judgmental strategy (heuristic versus systematic) and justification (of either believing or disbelieving the narrator), and in the interpretation of the very same heuristics.
Overall, the data showed that in credibility judgment laypersons and professionals process information differently: analyzing the very same statement, the former tended to consider it as true, whereas the latter tended to consider it as false. These data may partially account for the observed
biases in credibility judgment of laypersons and professionals.