Stimuli and task
The stimuli and task have been described in previous publications (Korb et al. Participants were instructed to indicate for each video the moment at which the first expression changes into the second, by pressing with their left middle finger the arrow-up button on a small number keypad. In each trial, a fixation cross was shown at the centre of the screen for 2–3 s (average duration 2.5 s), immediately followed by the video (5 s), and a feedback screen for 1 s. The feedback screen was blank in correct trials, while it contained the text “Do not forget to press” if no button had been pressed during the video, the text “Wrong button (only arrow up)” if the wrong button had been pressed, or the text “Please press only once” if the correct button had been pressed more than once. The task was preceded by four practice trials.