Familiarity-Related Fillers Improve the Validity of Reaction Time-Based Memory Detection

The reaction time (RT)-based Concealed Information Test (CIT) allows for the detection of concealed knowledge (e.g., one's true identity) when the questions are presented randomly (multiple-probe protocol), but its performance is much weaker when questions are presented in blocks (e.g., first question about surname, then about birthday; single-probe protocol). The latter test protocol, however, is the preferred and sometimes even the only feasible interviewing method in real-life. In a first, preregistered, experiment (n = 363), we show that the validity of the single-probe protocol version can be substantially improved by including familiarity-related fillers: stimuli related to either familiarity (e.g., the word “FAMILIAR,”) or unfamiliarity (e.g., the word “UNFAMILIAR”). We replicated these findings in a second, preregistered, experiment (n = 237), where we further found that the use of familiarity-related fillers even improved the classic multiple-probe protocol. We recommend the use of familiarity-related filler trials for the RT-based CIT.