2.2 Procedures
Upon entering the laboratory, each participant provided informed consent, and was then randomly assigned a role of guilty or innocent. For all participants, a Chinese star’s name (“Dehua Liu”) was used as the target. Four other names were assigned as irrelevants. For the guilty group, the participant’s own name was the probe, whereas for the innocent group, the probe was an irrelevant name. Participants were unfamiliar with all of the irrelevant names. Participants from both groups received the same instructions: they were asked to imagine being arrested by police during an airport boarding procedure. To prove their innocence, they were required to pass a lie detector test.
After placing EEG electrodes on the participant, the lie-detection process began. The cohort was presented with a series of names on a computer screen; each individual was asked to respond to “I recognize the name” by pressing the left button, or to ‘ ‘I do not recognize the name’ ’ by pressing the right button (the response buttons were counterbalanced across participants in both groups). As an example, when presented with “Dehua Liu,” the response ought to have been, “I recognize the name,” since all participants were familiar with Dehua Liu. Note that participants were asked to answer truthfully, except in those cases where guilty participants were presented with their own names. In this instance, participants were asked to lie by answering “I do not recognize the name,” thereby denying all guilt. The lie detector then determined whether the participant was lying, and provided immediate feedback. Feedback “+4” meant that the detector interpreted the response as truthful, whereas feedback “-2” indicated a “lie.” However, unknown to the participants, these feedbacks were presented randomly.
Participants were seated roughly 1 meter away from a computer screen. Each trial began with a 500 ± 100 ms fixation point, following which a name was presented for 300 ms. In response to the name, participants were instructed to press the appropriate button as quickly and accurately as possible. After a 1000 ms blank, a pentagram appeared on the screen for 2500 ms; this signified that the lie detector was analyzing the veracity of the response. Finally, feedback in the form of a ‘ ‘+4’ ’ (telling the truth) or ‘ ‘-2’ ’ (telling a lie) appeared for 1000 ms (see Figure 1).
Thus, the feedback stage inhered in four conditions: probe-truth (success); probe-lie (failure); irrelevant-truth (success); and irrelevant-lie (failure). The target repeated 60 times with real feedback, which was provided according to the participants’ real performance. The probe and four irrelevants repeated 60 times; 30 of these were followed by “+4” feedback, while the other 30 were followed by “-2”. Thus, there were 6*60 = 360 total trials. After sets of 40 trials (approximately 4 minutes), participants were given short breaks. The experiment lasted roughly 37 minutes.