A system and method of deception detection is disclosed wherein T trials are combined with P and I trials. Denoted as the complex trial (CT) protocol, in one embodiment, the beginning of each trial is indicated by the onset of a stimulus which is either a P or I, which remains on the display terminal for particular random (unpredictable to the subject) time period. At the expiration of the period, the stimulus remains on the screen, but is altered/augmented in some way, such as by color change. The subject has been instructed that if the color change is to green, for example, the trial is a target trial, and the subject should make a "yes" (target) response. If the color is anything else (e.g., red, blue, yellow), the subject must give a "no" (non-target) response. Accordingly, in the CT protocol, the subject must attend even more intensely than in prior 3-stimulus protocols to the probe-irrelevant attribute (i.e., the color change) of the initially presented stimulus, because the target/non-target attribute is brief and its appearance is made unpredictable via the randomly varying property of the presentation time period. That is, the subject must keep fixating on the white stimulus, or else he will miss the target/non-target presentation. He is aware, as before, that missed targets and non-targets will betray lack of cooperation with the procedure. Further, the disclosed system and method promotes maintained vigilant attentiveness thereby reducing the effectiveness of countermeasures.