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Picture viewing paradigm. There were five sessions. Each session lasted 7 min. A total of 60 IAPS pictures, including 20 pleasant, 20 unpleasant, and 20 neutral, were presented in each session, the order of which randomly varied from session to session. Each picture lasted 3 s and was followed by a fixation period referred to as intertrial interval (ITI) (2.8 or 4.3 s). Participants were required to fixate on the cross in the center of screen throughout the session.
