An ERP-based, control-question lie detector analog: algorithms for discriminating effects within individuals' average waveforms

Abstract

Two experimental, P3-based analog control question tests were run. In both, guilty subjects were presented with a set of seven phrases describing antisocial acts of which they were innocent, plus one phrase describing a guilty act (the analog relevant question), and one act to which a "yes" response (yes-target stimulus) was required to assure attention. Innocent subjects (run only in Experiment 1) saw all innocent acts plus the yes-target act. Thus nine acts were seen by guilty and innocent subjects. In both experiments, all subjects had to selectively review their guilty acts privately. Also in both experiments, all subjects were especially questioned about four acts of which guilty subjects were known to be innocent of all but one, and of which innocent subjects were known to be innocent of all. (These falsely accused acts were regarded as control question analogs.) In Experiment 1, the private review and rehearsal took place on the same day as the main test. In Experiment 2, one subgroup (delay-only) of guilty subjects was run as in Experiment 1, except that the private review-rehearsal was separated from the main run by 7-14 days. Another subgroup (delay-rehearsal) of guilty subjects was run just as was the subgroup delay-only, except that the delay-rehearsal subgroup additionally received a non-selective additional interrogation/rehearsal on the delayed main run day. Parietally maximal P3 responses were obtained to yes-target items in all groups. In Experiment 1, only in the guilty group was the relevant-minus-control P3 amplitude difference significant. In Experiment 2, the difference was significant only in the delay-rehearsal subgroup. A four-step algorithm (involving relevant-control amplitude differences and relevant target vs. control-target cross-correlations) was used to assess effects within individuals. In Experiment 1, 12 of 13 guilty subjects and 13 of 15 innocent subjects were correctly diagnosed. In Experiment 2, 3 of 8 delay-only subjects and 7 of 8 delay-rehearsal subjects were correctly diagnosed. In Experiment 2, the relevant-minus-control group P3 amplitude difference was significant in the delay-rehearsal but not in the delay-only subgroup. The results suggest that temporally proximal, non-selective rehearsal procedures are sufficient to activate personal knowledge of a salient (oddball), P3-generating stimulus phrase, and that even selective rehearsal of guilty acts is not sufficient without temporal proximity.