Familiarity-related filler items enhance the RT CIT, but not the P300 CIT: Episodic vs. Semantic memory protocols

The reaction time-based concealed information test (RT CIT) typically uses three types of stimuli: 1) probe (i.e., crime-related item), 2) irrelevant (i.e., crime-unrelated item) and 3) target (i.e., an irrelevant item assigned a unique response so as to ensure attention to the test). Lukács, et al., (2017) introduced familiarity-related filler items to the RT CIT, enhancing the efficacy of the test for both single and multiple probe (per block) protocols. Our study aims to A) replicate the effects of familiarity-related filler items on the RT CIT, B) use P300 to investigate the mechanisms of the fillers-related enhancement effect on the RT CIT, C) investigate whether these fillers can enhance the efficacy of the typical P300-based CIT, and D) explore the effects of fillers on the semantic and episodic versions of the P300 and RT CITs. We replicated a clear fillers-related enhancement of the RT CIT (N = 38 for Fillers, N = 37 for No Fillers). Semantic and Episodic experiments were enhanced equally-well by filler items. No effect of fillers was observed on P300 amplitude for CIT stimuli, however, an interaction involving P300 latency suggests that fillers facilitated the processing of Semantic information over Episodic information. Our study independently replicates a valuable improvement of the traditional RT CIT, investigates the potential mechanisms of this enhancement effect, and demonstrates important differences between the P300 and RT CITs.