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(A) Examples of the pictures (Left panel: painful picture; Right panel: non-painful picture); (B) Structure of one trial. Each trial started with a 500 ms fixation, after a 400–700 ms random blank interval, the picture appeared for a maximum of 2000 ms and the participants were supposed to judge if the picture was a painful one or a non-painful one as soon and accurately as possible. The picture disappeared when a response was given. The ISI between trials was 800–1200 ms randomly.
