Materials & Methods
Participants. Twenty right-handed healthy participants (age 22.39±3.82, ten females), were recruited for this 2-day experiment. All participants were recruited from within the student population in the Stockholm area and were of Swedish ethnicity (Caucasian). All participants gave their written informed consent before participation and were naive to the purpose of the experiment. The procedures were executed in compliance with relevant laws and institutional guidelines, and were approved by the Regional Ethical Review Board of Stockholm. Participants were paid for their participations.
Conditioning paradigm and physiological assessment. The experiment took part over 2 days, Day 1 involved the fear-conditioning paradigm in functional MRI (fMRI) setting, and Day 2 involved a recall session followed by questionnaires, Cyberball and IAT outside of the scanner.
Day 1: On Day 1, participants were submitted to a delayed conditioning fear conditioning protocol that was directly modelled on previous studies (Olsson, Ebert, Banaji, & Phelps, 2005). Participants were told that they would see visual images on a screen while sometimes receiving shocks. The instructions were to pay attention to the screen, throughout the whole experiment. No distinction was made between the Acquisition and Extinction phase to the participant. Conditioned stimuli were composed of images (selected from a face database provided by Jennifer Eberhardt of Stanford University) of two White and two Black American neutral male faces that appeared on a computer screen. Before the procedure, skin conductance electrodes were attached to the second and fourth distal phalanges of the left hand, and the shock electrode was attached to the right wrist. Each stimulus served as both CS+ and CS- counterbalanced across subjects. All stimuli were presented for 6 seconds with a mean interstimulus interval (ITI) of 12s. During the initial habituation phase, subjects saw 4 non-reinforced presentations of each CS. During the subsequent acquisition phase, they saw each CS 9 times, with every presentation of a CS+ co-terminating with a 200-ms shock, and the presentation of a CS- never paired with a shock. Finally, the extinction phase included 12 non-reinforced presentations of each CS. The order of presentation within each phase was randomized. Subjects had an electrode attached to their wrist that they were told would be used to deliver mild electric shocks, cable leads were magnetically shielded and grounded through an RF filter. The subjects were asked to adjust the level of the shocks themselves through a standard work-up procedure prior to the scanning session. The shock level was gradually increased until the participant experienced the shock to be “uncomfortable” but not “painful”. Skin conductance was measured with shielded Ag-AgCl electrodes filled with Conductive gel (Signa, Parker). The electrode cables were grounded through a RF filter panel, and the SCR was sampled...